Mk VII 50AE Modern Barrel Issue...

[MrBlackCat]

I searched a bit and didn't see any posts about this issue... maybe someone can shed some light here.
I bought a Mk VII 50AE Desert Eagle in 1993. I have shot it about 3000-3500 times over the years as it isn't exactly a plinking gun. The only issue it has ever had were caused by weakening springs or deteriorated extractor nub/spring. I can't say it has never failed, but it is extremely rare.


So I bought a new 50AE Barrel with the intention of having a muzzle brake installed... I didn't want to modify my original firearm. I thought I better test it before having the work done, and to my amazement, it basically doesn't work. The symptom is failure to feed... empty chamber. Extraction is perfect, but it has never fired more than two shots in a row without manually racking the slide.


I dropped my original barrel back in and fired 14 shots, mixing limp wristed with iron-grip in there, factory MR 300's and 350's perfect, as always. Even tried one of the new magazines and it worked fine, with my barrel. Dropped the new barrel back in, and converted it to an instant 1 or 2 shot max. It does manage to set the hammer without fail however, so the gas port isn't completely blocked or anything close.


This issue got me looking around on the internet and have spent a few hours reading the horror stories of Desert Eagle pistols... while my experience is based on one firearm, it is more like a perfectionists love story. I know all about the issues that arise from grip, weak springs all around etc... but this issue is something I have no experience with.


My questions might be...
Gas port issue?
Compatibility issue? (with early Mk VII 50AE)
Bad barrel?


I also bought a 44 Magnum barrel, which I have not fired yet... I will try it soon and see what happens... if I get many failures, I will assume there is something strange about this particular Mk VII.


I am not a gunsmith, but I am a machinist. I checked this barrel very closely against mine and could find nothing different with most dimensions relative to function. The barrels are made completely different. My original is a two part barrel with completely different machining and the inlet gas port at 7 o'clock... while this new barrel is single part and 6 o'clock gas port.


I think tomorrow I will take the springs out and cycle it carefully and see if I can feel anything dragging.


Anyway, thanks to anyone who reads this and thank you in advance to anyone who can help. I am open to most any suggestions.


MrBlackCat

[gb6491]

MrBlackCat,
The Desert Eagle is far out of my wheelhouse, so I'd just like to say welcome to the forums :)
Regards,
Greg

[Bawanna]

Ditto what he said for me too. I did get an intimate tour when they first came out at a sportsman show or maybe an NRA show in Seattle. The rep took it apart down to every single piece. At the time they only offered 357.

It was a beauty to behold inside, very well machined. Wanted one ever since but never got one.

I officially proclaim you our resident Desert Eagle authority. I'll keep watching to see how this pans out.

[MrBlackCat]

Thank you for the welcome and replies gb6491 and Bawanna.

Understandably, Magnum research says they can't do anything without sending the firearm, which I expected would be the case. I will just have to eat this one I suppose. I wouldn't even consider returning a near perfectly functioning firearm to have it potentially modified to work with a new barrel. The concern would be a change that might compromise the original functionality or compatibility with the original barrel.

The next step is to try the new 44 magnum barrel and see if it suffers from the same issues. Part of me says I should just return the unused 44 Magnum set at this point. But it might tell me if this is some odd original tuning to this early model. I will be quite unhappy if I have to eat $800+ worth of pistol barrels as opposed to just $400+.

Next I will try to dye the shell casings and see if the slide drag marks can tell me anything about how far the slide goes back.

I will continue to update this as it might help someone else in the future, especially if a resolution is found.

Edit: Another thing occurred to my while blowing through the gas ports on these... the modern gas port seems to have less volume, although I have no way to measure this. I wonder if between piston wear and dirty cylinder I get better pressure to the slide with my original barrel. I think I will try a new piston and see if there is any effect.

MrBlackCat

[MrBlackCat]

Double post for the purpose of separation of updates...

Well, I got some 44 magnum ammunition today and tried the new 44 magnum barrel. Perfection, as the with the original 50AE barrel. I shot iron-grip to one handed limp-wrist... perfect. 200 rounds and the brass was stacked like firewood. (ok, not really, but it was extremely consistent.)

Todays test session started by field stripping and bolt removal. I changed all springs, cleaned and oiled (super light, as usual) even though I am a couple hundred rounds early for service, and not experiencing any malfunctions with the original 50AE barrel, and the brand new 44 Magnum barrel. The cost of a rebuild kit is minor compared to the cost of ammunition anyway.

With everything new, I loaded up a half dozen 50AE magazine and changed to the new 50AE barrel...
I started with 350grain Magnum Research (Speer) loads. First shot, I iron-gripped it, and it fired and successfully loaded round two. Second round fired, and stove-piped round three. Cleared, iron-gripped, stovepipe, and variations of this for three magazines... enough.
Well, this is a NEW problem anyway... at least the slide was traveling back far enough to scrape off another round.

Long story short, the new 50AE barrel has not successfully loaded more than than one round. Determination... the new 50AE barrel has some substantial issue. I believe if this was a compatibility issue specifically with my firearm, the new 44 magnum barrel would have exhibited at least some of the issues.

Maybe the port has a bit of something in it from the factory. The new 44 Magnum barrel is designed exactly like the new 50AE, so it isn't likely the barrel design change (compared to my original) that is causing the issue with my very early model 50AE, as I suspected earlier.

I so wish I had another barrel to test... if someone is willing to rent me a test barrel, I will gladly do so. I am really curious about this now. I would like to believe I just have a bad barrel.

If this was a ramp issue, an ejection issue or anything related to those functions, I could fix it... but if this is a gas port related issue, there is not likely anything a user can do.

Next step will be to take this barrel to the test lab at work and see if I can devise a way to test the gas port flow... since I have a perfectly working 50 and 44 to compare to. If I can rule that out, then I can move on to "drag" maybe.

I will also note that while I had the springs out of "everything" I tried a number of comparisons of "drag" relative to bolt engagement into the barrel etc... I was unable to detect any differences in the three barrels.

One thing is sure... the new 50 AE barrel is not able to back the slide out far enough to operate properly.

Update soon.

MrBlackCat

[MrBlackCat]

Update...

Borrowed a co-workers Mk XIX 44 magnum which is a few years old (maybe 4 to 6) and the new 50AE Barrel was basically a single shot on it also. Exactly the same symptoms as my Mk VII... His 44, my new 44 and my old 50AE works perfectly on both guns.
Something is wrong with this new 50AE Barrel...

As of now, I have re-emailed Magnum Research to see if they will take the barrel back and test it without me having to return my perfectly working firearm with their not working barrel, then go through a gun dealer etc to get my gun back.
Something tells me that if they get this barrel working on any Desert Eagle, it is going to work on mine.

I will update this thread with the reply...

MrBlackCat

[gb6491]

Thank you for the updates!

[MrBlackCat]

Thank you for the updates!Resolution or not, at least this can be available for others to find should they have similar issues.

Well, Magnum Research won't test the barrel or take it back without my firearm.
Ouch... a could have gotten a boat anchor for a lot less than $415! I don't really consider this standing behind your product.
<sigh> I understand their stance a little bit, but apparently these guns CAN be a bit problematic, and because mine functions basically perfect with my original barrel, and the new .44 Magnum barrel, I don't want my gun modified, or even potentially modified, just to work with this one barrel that I consider defective. What if I got it back and it doesn't work with my other barrels? Magnum Research would have no liability and I would just be out my near perfect firearm. Another thing is that getting the gun/barrel working over a couple of clips of ammo is one thing... but what about over 1000 rounds? A gunsmith doesn't test that... they can't. No one rational would consider this, in my opinion. There is also potential mail loss, then retrieval from a gun store as they can't ship them back directly to you etc... I will just eat this one... and I won't be buying any more barrels for sure. The .357 was to be next if this went well... but. After I recover from $1000+ in barrels, parts and ammunition, I will just buy a modern Mk XIX in .357 Magnum, as it would have been tested for function, apparently unlike this barrel.

Next steps...
Because it seems the slide is unable to travel backward far enough to function properly, I will try to test for two things.
1. Gas flow.
Maybe the port is partially blocked.
Maybe the cylinder is out of spec. (I checked this with calipers, but I will test it with higher precision)
2. Drag.
Maybe the chamber is binding the shell, taking momentum off the slide.
Maybe the bolt lugs are binding against the barrel during unlock rotation.
Maybe the sides of one or more bolt lugs are coming in contact with the barrel lugs.

Even though the new .50AE Barrel is made quite different from my original/old .50AE barrel, I have it for reference. And I also have a perfectly functioning brand new .44 Magnum barrel for comparison, which is manufactured the same. I have to add that the .44 Magnum is SO nice to shoot on this platform... one handed rapid fire is very possible. I might go ahead and have a brake installed on the .44 barrel to soften it even more. I like to break my targets, not my wrists. :)

Again, if anyone has any suggestions of why this might be failing, or additional tests I could try, please let me know.

MrBlackCat

Edit:
1. Gas Flow...
I don't have any pin gauges here at home, so I used precision calipers to check the diameter of each barrels gas cylinder...
~0.3957 (Original, should show some wear .50AE)
~0.3966 (New .44 Magnum)
~0.3984 (New .50AE)

That seems like a lot more clearance for such a small piston/cylinder.

Maybe someone can measure their Desert Eagle gas cylinder(s) and let me know how theirs compare...

I am going to start leaning toward excess clearance in the gas cylinder... I will figure out a way to test this. I might grease the piston between shots for additional (though VERY temporary) seal.

Another way I could test the slide in general would be to keep a little pressure on the slide lock and see if travels back far enough to engage with each shot... but I think it is clear the slide isn't traveling back far enough. Kind of sucks I used a new spring kit that I really didn't need to. I saved the parts though. At this point I have over $1000 in barrels, testing ammunition and test parts. At least the .44 Magnum works like my original barrel.

[MrBlackCat]

Anyone have an opinion on modifying the springs to test for low gas pressure? If this were the issue, say from excessive clearance in the gas cylinder, then lighter springs would at least allow the slide to travel back a bit further, even if it wasn't able to put the slide back into battery.

I have a set of old springs I could modify to test this... or what about removal of the inner springs I have read of?
If this didn't help function, I would at least know to look elsewhere to try and resolve this.

Any thoughts or suggestions would be appreciated.

MrBlackCat

[MrBlackCat]

Update...

Been busy, but tonight I got a minute and swapped to an old set of springs I took out from a few years ago. A bit weak, at approximately 3/4" shorter uncompressed, than some new springs I have... but I took out the inner springs just to test it. It actually worked perfectly with my average grip... I didn't need an iron grip, and I didn't try limp-wristing it, but it worked perfectly for three magazines. I knew it was "close"

So what next?

1. Maybe that extra three thousandths of clearance on the gas piston is too much?
2. Maybe something is dragging somewhere, defeating some of the slide motion?

Again, any suggestions or insights would be appreciated.

MrBlackCat

[MrBlackCat]

Update...

Got a new Spring Frame/Set, a new piston, and some other stuff.
First I checked the dimensions of the new piston... it is almost identical to my current piston in dimensions... maybe a few ten-thousandths, but nothing substantial compared to cylinder differences.

First test, I put my weakest set of old recoil springs back into the gun, but this time including the inner springs... again, the new barrel performed excellent for 14 shots. Enough for me to say "is working".

Next test, I put the new piston and new springs into the gun and loaded up 350gr this time. Wouldn't load these... it either failed to pick up the round completely, or grabbed the round between the rim and the case body for a stovepipe. I dropped my original barrel back on and it fired perfectly for another magazine of 350gr rounds.
I switched back to Hornady 300gr (because that is what was in the next two magazines) and the new .50AE Barrel. It was able to load the next round some of the time, even twice in a row once... but mostly fails to travel back far enough to pick up the next round.

As usual, my original barrel shoots every round without prejudice... the new barrel functions with my oldest, weakest springs and Hornady 300s.

Not sure what to think, but I am going to keep with it until I can figure out what is wrong, and how it might be resolved.

MrBlackCat

[gb6491]

MrBlackCat,
Thank you for the updates! They are an interesting read for me, especially so as I have very little hands on with the DE.
I would like to ask if you have looked for any differences (maybe to the point of using layout fluid) on the barrel surfaces that the bolt locks into between your different barrels?
Anyway, that's just a novice's thought; please continue with your updates.
Regards,
Greg

[MrBlackCat]

Hello Greg (gb6491)...
Thank you for the reply.
Barrel to bolt drag is something I have considered and is on the list. As hard as this barrel material (in my opinion it is very hard) break in would be really long term. This is pretty hard to locate and measure just because it has to be shot to see wear points/patterns reliably, but I do intend to try this.

So far what is "proven" is that the slide doesn't come back far enough to pick up a new round, most of the time... but I have yet to determine for sure if this is drag or lack of gas pressure transferred to the slide. I will continue testing.

One way to look at it, is that hard carbon does build up in the cylinder... which should decrease clearance/blowby in the cylinder. I just need to bore it out and sleeve it maybe. ;)
One suggestion was to make a new piston a bit over-sized to fit the slightly larger cylinder. This is a consideration as this problem seems to be so close to the edge of functioning.

Unless I prove this barrel is out of spec in some way, I still don't hold any ill feelings toward Magnum Research... they wanted the entire gun back because the barrel is part of a system. My issue with that is that my "system" works perfectly under any conditions except with this new barrel.

Next: I am going to use a dental mirror and microscope to examine the inside of the barrel/lug area for burrs, and use dye and hand operation to look at contact points and concentrated pressures, then compare these areas to my existing barrel and see if de-burring is needed. I have to say... my original barrel shows a lot of sharp edges in this area still... after thousands of rounds... this is one reason I believe this barrel material to be a bit more hard than average.

On a side note, the new .44 Magnum barrel has worked flawlessly, from the first shot, with five different brands of ammunition so far. That is the Magnum Research I know and expect... now if we can just get this .50AE barrel working, that expectation won't be reduced.

MrBlackCat

[MrBlackCat]

Update...
Got a minute to try something else.
I found the lowest power/velocity rounds I have are the Armscor USA 300gr, at 1200fps. I fired them in my original barrel with no issue, as usual. I changed to the new .50AE barrel and it was unable to push the slide back far enough to load a round from the magazine. Actually the barrel was unable to get the slide back far enough to even eject the round... as expected.


So I decided to increase the gas pressure to the slide... I figured the best way to do this was to dip the piston in wheel bearing grease. Messy, but effective. It worked perfectly for one shot each time. It loaded the next round perfectly with the extra seal created by the grease.


SO... I don't want to remove the barrel and dip my gas piston in grease for every shot fired. I thought I might try to sleeve the barrel cylinder, but it is too close to the barrel diameter and the barrel material is very hard.


My plan at this point is to make a larger piston. I will do this by building up an existing piston, or possibly turning a new one. I will consider this a resolution. I will report back if this is successful.


Even though this is a resolution, I still wonder if the extra pressure is needed because of drag in the bolt area, or simply because too much gas is escaping due to the over-sized cylinder.


MrBlackCat

[MrBlackCat]

Update...

It will now fire any factory ammo I have. Is this good? Not really. Turns out my first suspicion was correct.
Because this thread has a lot of longer posts in it, I will re-cap as this is probably the end of the line.

The story, kind of like in Cliff Note form...
------------------------------------
New .50AE barrel failure to feed all but the hottest of factory loads, can't lock slide back, and even those 300 Hornady's were unreliable loaded.

Measured new .50AE against my old .50AE barrel... almost identical less manufacturing differences (2 part barrel vs 1 piece barrel)... EXCEPT for the gas port, which was about .003 (three-thousandths) larger on the new, malfunctioning barrel. Borrowed a co-workers few year old Mk XIX and had exactly the same result as with my own Desert Eagle. New barrel now doesn't function on two Desert Eagles... getting harder to blame issue on something with my gun.

So... tried new parts, old parts etc.
At this point I was able to verify that the slide was NOT traveling back far enough to function properly. Some video showed this EVEN when the gun did load a second Hornady 300gr, the shells didn't eject well compared to my original barrel with ANY factory ammo, lowest power to highest.
------------------------------------
Yesterday, I cleaned and dyed both .50AE barrels at the bolt receiver area and fired them. I inspected them both carefully for contact points and found them almost identical and nothing I consider unexpected or unusual.

The O-Ring...
So today I decided to go all out in the direction of "The damn cylinder is too large and out of spec" (yeah, I am not very tolerant of premium priced items with non-premium quality these days, so I am wearing thin here.)
Anyway... I stuck on o-ring on a new piston. Fired for 6 shots with just enough power to eject the shell onto my face, my hearing protection and sometimes roll off my hand to the ground, until the o-ring failed... this is with the Armscor/lowest power rounds I have, and new springs.

The Piston Build Up...
So I took the new piston and built it up in its flats and turned it back to .3915. So now I have a round piston, with no flat at its "rings" Risky? Maybe, but I know the gun well and was confident it could handle one time of bottoming out really hard if this was a bit too much. Well it didn't bottom out. It couldn't even load a second round. It didn't even come back far enough to catch a round between its case and rim to stove-pipe it! So I came in the house and found a couple of ways and formulas to look at gas flow with cylinder volume... those three thousands of extra clearance are too much area because of the pressures involved.
Here is something you can relate to... remember how boring out a cylinder .040 or .060 was enough to change the horsepower of an automobile at gasoline combustion engine cylinder pressures? Exactly... now consider the tiny percentage of diameter difference that .040 to .060 was compared to a cylinder around four inches in diameter.

The point... too much gas pressure loss due to in the cylinder to piston clearance is the problem with this barrel. So I built the piston flats up and brought it down to ~0.3945, then added some smaller flats back to it. (3-thousandths larger? Holy hell... I know) As calculated, it runs perfectly so far. It doesn't sound like much to have 3 thousandths difference, but if you look at the change in clearance between the piston and the cylinder, there is a 68% increase on the new barrels cylinder. That is a lot... and that is too much.

I would like to point out now, that this modified piston won't fit or even "start" in my original barrels cylinder. (I feel like I should type that part twice...)

Will this work?
Is this safe?

I doubt it... the welding would have compromised the hardening process of the piston, and I have no way of knowing what grade/type of metal it is. Even though the worst case pressures will not likely exceed what even mild steel can take, the stem is really thin.

I haven't gotten anywhere with Magnum Research just looking at the barrel without sending my gun, so I am going to try one more time with this information and see if they will have a look at it. This has become pretty straight-forward at this point... the barrel is out of spec.

MrBlackCat

[gb6491]

Thank you for the detailed up date, I admire your approach and method.
Here's hoping they just exchange that barrel with you. I too, dread sending my machines to anyone when I have the tools and skill to do the work, but lack only the parts they have.
Regards,
Greg

[MrBlackCat]

Thank you for the detailed up date, I admire your approach and method.
Here's hoping they just exchange that barrel with you. I too, dread sending my machines to anyone when I have the tools and skill to do the work, but lack only the parts they have.
Regards,
Greg
Thank you for the reply.
The fact that this barrel has the same issue on a another Desert Eagle should be enough for them to take the barrel back at least to check it. Maybe then, if it didn't have an issues have me send my gun in... which I would not have to do. I am fairly confident at this point that a simple check on their part to start with would have shown this issue. The MRI repair guys are going to know immediately what the tolerances are.

In my last email to Magnum Research about this issue, I sent them the cylinder vs piston dimensions and asked that they at least run these dimensions by someone in repair... I got no response. Not sure if they can't do this, or just have to assume that everyone is an unmotivated moron first. The latter being understandable these days it seems. As I said before, I would not even consider sending this gun anywhere... that option isn't on the table as the gun is in perfect condition, and the barrel isn't likely to function correctly on any gun they try it on.

Another consideration is that I sell the barrel for say half new with this issues and its history up front, to someone who isn't concerned with sending their firearm to MRI... then they will be getting a new barrel I can just about bet you.

I will try to talk with them again and see if they will consider taking the barrel back, if not, I will just have a bad barrel to figure out what to do with. Just because I can make a new piston that works doesn't mean it is a good or safe idea. Besides safety and function, I would also have to change the barrel and piston any time I want to change to my other two barrels. Dropping your piston in the field isn't the end of the world, I got spares, but dropping your CUSTOM PISTON in the field... yeah. Can I make another? Of course, but I shouldn't have to. This won't be the first time I have had a product be bad and then myself as the consumer, got to eat it. In their defense, MRI offered me an option... just not one without what I consider great risk and inconvenience.

MrBlackCat

[MrBlackCat]

Update...

Well this is positive. I sent a one page outline of the testing and results to Magnum Research asking them to reconsider testing the barrel without my firearm.
This time, there was a day or so delay in the response time... but it seems it might have been worth the wait. In my previous contacts with Magnum Research support, they wanted me to send my Desert Eagle in with the new barrel. Of course I didn't want to do this, but of course, they believed they would need my gun to see what the problem was. My main resistance to mailing my 23 year old Mk. VII .50 gun in was that it works perfectly and always has. It even worked perfectly so far, with my new .44 Magnum barrel. But I wanted a muzzle brake, so I bought a new .50AE barrel to have it added to as I didn't want my original gun modified. But the .50AE barrel doesn't cycle the slide.

This email was different though... I suppose it finally got to the right person, or maybe was thorough enough to be taken seriously. Here it is...
****begin paste****


By all means, please send that barrel to us to inspect. We will check it out and test it and if doesn't pass, we will replace it for you. While it is here, we can also install the muzzle brake if you wish.
You can send the barrel and a short note with the issue described to:


Magnum Research Inc
Attn: Customer Service
12602 33rd Ave SW
Pillager MN 56473


Magnum Research Inc.
Customer Service/Tech Support
Phone (218)746-3459
Fax (218)746-3097

****end paste****

Simple, clear, positive, and what I wanted to hear. I am still curious as to why this wasn't an option before I went to such great lengths to verify the cause of the issue. I am always glad to learn about new things, as I did with this "journey" of determining what was going on with this barrel. I am confident Magnum Research will find the same issue. The advantage will be that they already know the dimensional specs on the barrel. What took me around 10 hours total time to determine (swapping spring sets, making the new piston, test firing etc), they can probably know in a couple of minutes. My other disadvantage was that I suspected my gun being so old might have some other incompatibility. In fairness, it does say "Mk XIX only" on the packaging of both the new .44 Magnum barrel, and the .50AE barrel, and my gun is a Mk VII, although that isn't supposed to matter in the .50AE as they were to become the new platform anyway.

I will follow up again when I hear from Magnum Research.

MrBlackCat

[gb6491]

I imagine they deal with all types thus the send the whole thing in thing. It's heartening to read that once they realized you have some skills they adjusted the plan.
Please keep us advised on how this plays out.
Regards,
Greg

[MrBlackCat]

Update...


Magnum Research called today. My barrel is "within spec" and it seems there is nothing wrong with it. They asked for payment for installing the muzzle brake and they would send my tested barrel back to me. The only thing noted done was pretty standard... they polished the bolt lug area. Hmm... ok. Maybe I should ask to purchase their test gun... as it seems to be AMAZINGLY adaptive. (maybe the test gun springs had 5000 rounds on them?)


I will refrain from saying most of the negative things going through my mind right now.


The positive... the person I spoke with was polite, cheerful and listened to my entire statement of surprised distress as I explained to him a tiny bit about some of my journey to discover the over-sized cylinder issue. He listened a lot... and heard it. He just takes the calls and payments though. The only negative thing relative to our conversation was his statement of "if it doesn't function correctly I could send the gun in and they could repair it." (My thought was "that doesn't seem likely") If they don't even realize the gas cylinder was out of spec, they aren't touching my firearm. Now the 1% of potential of me sending my Desert Eagle in to be looked at, just became 0%.
(Damn... and this was a positive section of the post!)


So now I have a muzzle brake on a bad barrel. Great. A $450 boat anchor just became a $660 boat anchor... well, now its heavier at least. I suppose I need to get me a boat now.


It was kind of sad as the sales guy made a couple of statements that in my opinion shouldn't exist... the main one was something about how these guns generally like only one kind of ammunition. I quickly pointed out that my Desert Eagle didn't have this limitation, and never has. With statements like that, it does raise my sympathy toward Desert Eagle owners who claim to have experienced this. I have unjustly had a tendency to blame the individual, rather than the gun, because of my near perfect experience with my own Desert Eagle.


I suppose this thread has about run its course, as there isn't any resolution from Magnum Research. I am on my own from here on out.


The main thing I am saying now is "Thank GOD I didn't send my gun in!" Fixing the parts that don't need fixing is really sad. At least I dodged that bullet. (pun intended)


Oh well


Potential next steps...
Not sure exactly what I will do, but I will put the defective barrel in a drawer until I cool off for a few months as this has been a really negative experience for me.
A. I may learn a bit about the metal these pistons are made from and produce a couple of really nice ones to use with just this barrel. Sure leaves a bad taste in my mouth though. I will learn what I need to and do it right.


B. Sell the barrel to someone with this problem up front and get another, which isn't likely to have an out-of-spec gas cylinder... then they can send their gun in and play dumb and likely get a new barrel. I have a suspicion something I have experienced before might have happened. Sometimes people of one profession react poorly if they feel someone from another profession is trying to tell them theirs. Just speculation, but my thoroughness has brought this reaction from others before. As I stated before, I don't know the specification/tolerance of the gas cylinder to piston clearance, but I know math and logic, and obviously how to test it... and it worked. I don't have to be a doctor to know when a bone is broken. Again, I made a piston with the same clearance as my original barrel to piston clearance, and it worked... and the piston I made that enables the barrel to work, won't even fit inside my original gas cylinder. How do you even argue that?


While the money doesn't bother me that much, having something that doesn't work bothers me... now I am kind of leery of buying another Desert Eagle... especially if the modern ones are so inconsistent they can only work well with one particular round.


On a positive note, should I choose the new piston route, at least I can actually use the barrel with seemingly any round, like my original barrel.

MrBlackCat

[Steamdonkey]

Hmm... My new DE50SRMB has the same ~0.3984 measurement (as measured with $30 general purpose digital calipers). It ran flawlessly through 60 rounds (using 3 different mags) yesterday at the range, but this piston clearance issue still makes me nervous. I've only tried it with Underwood 300 gr JHP, which is on the warm side at a claimed 1580 fps.

[MrBlackCat]

I understand... With Hornady ammo, and a super clean/slightly lubricated slide rails, my gun with function with a standard piston, most of the time, but the case ejections are weak. The ammo toward the lower end of the pressure spectrum will not come close to functioning the slide. If I pop my original barrel and piston on there, the ejection distance is close to three times the distance with the American made barrels.
With a few thousand rounds through all nine barrels at this point, it is clear that the Israeli barrels are superior relative to function. One consistency is the diameter of the gas cylinder. They are all exactly the same. The American barrels I have are all over the place in gas cylinder diameter, and their function reflects this. I will replace each of my American barrels with Israeli models as I find them because of this.

As long as it is functioning, there is no concern in my opinion. If you buy some bulk American Quality or Armscor 50AE (https://www.outdoorlimited.com/ProductDetails.asp?ProductCode=fac50aevp250) (.86/Rnd stuff of which I shoot thousands of rounds per year) you will quickly find out of your gas system is within spec. These ammos are at the fringe of what will function in the US Barrels I have, and will not function in my US .50AE barrels without my custom made piston(s).

MrBlackCat

[Steamdonkey]

Just curious, how are you measuring the gas cylinder diameter and how much variance are you seeing with the american made barrels? I'm not sure how well my calipers take measurements like this and I'm thinking about checking it with something else. By the way thanks for sharing all this information about your DE's and experiences with MRI / Kahr.

[MrBlackCat]

I am using a set of Gauge Pins which are two tens under (-0.0002) and I am using two different sets of bore gauges which I measure with two different sets of micrometers. Measuring in to the tens is not an absolute for many reasons, which is why I use second and third opinions with different tools/systems.
Calipers are only hitting one area and aren't accurate below a thousandth or two, with disregard to roundness, so that is limited in some ways. Gauge pins check for roundness, but only go in whatever increment you have gauge pins in. Bore gauges are relative to the users precision. I do use clutched micrometers on the bore gauge to be as consist as I can. When I get under/within four-tens (+/- 0.0002), with two different sets of micrometers, I record that average as accurate.
Also, you can measure the slack in a gauge pin (movement at its furthest point from insertion) and get a good idea of the relative clearance of a gas piston in a given gas cylinder.

More later... got to run.

MrBlackCat

[Steamdonkey]

Wow that sounds quite thorough. I messed around with a wood dowel and might revise my estimate to something in the .393" to .395" range, assuming the gas cylinder is actually round, which it probably isn't. I might try some reloads this weekend and I'll be curious to see how the suggested starting load of 29.7 gr. of H-110 does.

[MrBlackCat]

Here is a quick clip of a small part of a spreadsheet I did to look at the gas system with math... this is messy and for my own research, and this is just an input section to show some dimensions I pulled a while back. This will show you the amount of clearance and what it could mean to volume. I used the sheet to calculate the fluid loss that would result from the extra clearance. Even in the volume produced by the impulse at 30,000PSI takes a huge hit in potential slide popping energy from the clearances shown here.



Piston Dia

0.3910

Clearance



Cylinder Dia.
Clearance
Over- Value
Increase


.50AE Original
0.3952
0.0042
0.0000
0.000%


.44 Mag/US
0.3970
0.0060
0.0018
42.857%


.50AE US
0.3985
0.0075
0.0033
78.571%



Not sure if the format will be preserved enough to be clear... keep in mind the Clearance Increase is just that... not a measure of volume reduction. The volume reduction is fairly complex to calculate because of pressure over time with the factor being clearance volume. Pure volume loss isn't enough to accurately access this either, as this isn't a gas supplied from a mass volume like an air-compressor... because of the low volume from the high pressure impulse, pressure drop is not linear, but grows exponentially as the clearance increases. PI is not your friend with clearances like this under the conditions which the Desert Eagle works. They need the low clearance to really work well... the Israeli IMI/IWI seem to believe in this, as every Israeli barrel I have has virtually identical clearance in the gas cylinder.

I don't reload, but I can tell you this I have learned from use of a chronograph... with the same weight projectile, sometimes the faster round will NOT cycle the slide, and the slower cartridge will. Must be rate of burn creating a pressure over time. I can't recite these from memory, but I save almost all of my chronograph data.

MrBlackCat

[Steamdonkey]

Very interesting, especially the part where you mention ammo with a lower muzzle velocity can function better than higher velocity ammo. I don't recall the exact wording but the comments in the reloading book I have seem to suggest the recommended powders have a slower burn rate than typical pistol loads.

After seeing your gas cylinder diameters and after measuring the O.D. of my '5 in 1 tool' I have zero confidence in the numbers I've reported so far for my barrel. I'll wait for a more reliable measurement before throwing out another diameter estimate. :)

[Steamdonkey]

After meticulously narrowing down a brass feeler gauge to find the width that matches the diameter of the gas cylinder I'm calling it 0.397". More important than my measured diameter is the fact that the gun seems to work fine with medium power reloads. It didn't have trouble picking up the next round until muzzle velocities (300 gr.) dropped below ~1125 FPS and by that point the gun had 25 rounds through it and was a little dirty. After that I went to a slight hotter batch and shot 10 more rounds at 1175 - 1250 FPS with no issues. Well, my 3-4 foot groups at 100 yds are an issue but I can't blame the gun for that. :)

[MrBlackCat]

That sounds about right for a .397 in my experience. In my .44 magnum barrel with about a .397, I often demonstrate how it won't function reliably at all with a specific target load (Precision One 210gr standard, NOT XTP) using the standard size gas piston. Then I swap the piston for the one I made to adjust the cylinder to piston clearance down to Israeli spec... and it functions absolutely reliable. Note that Precision One makes a Desert Eagle specific 44 magnum round guaranteed to cycle properly in the Desert Eagle... this is not the round I am shooting... I am shooting their target ammo in .44

If I can group 3 ft at 100 yards, I am good. :) You can always just blame the ammo like they do in videos on the internet... "yeah, this ammunition isn't all that accurate beyond 15 yards..." I have yet to find a gun that shot SO bad I could actually say it wasn't accurate... but that is just me... and some days I can be pretty bad.

MrBlackCat