Fire Lapping a Barrel

[mr surveyor]

Has anyone here ever firelapped a barrel.... not just by firing a few hundred jacketed bullets and hoping for the best, but by handloading the lapping compound coated bullets (light charge) and firing/cleaning until the groups tighten up?

Reason I ask is in relation to my recently acquired SRH 44 mag. It's a pretty well known fact that many of the Ruger Super Redhawks have a slight (.001-.002") barrel constriction at the barrel threads, as do many orher revolvers. I don't know if I should expect any problems or not as I haven't put enough rounds down range yet, actually none from a sandbag rest, and no cast lead. I'll be loading some 240 gr swc's this weekend (if my dies come in that soon) and will have an idea what to expect. If it seems suspect, I buy a package of barrel slug leads and try to "feel" for the constriction ... and take the slug to a buddy with a precise caliper for later bullet size ordering. If it shows any constriction, I'm considering buying the inexpensive (about 20 bucks) barrel lapping kit from one of the bullet suppliers. I've never done it, never seen it done, nor do I know anyone personally with any experience with the procedure.

Looking for the voice of experience... I probably need a mentor for this.

surv

[CJB]

A fair number of ALL revolvers have a minor constriction at the barrel threads, depending on how tight they had to get it when they tried to make it line up. Normal crush factor for the shoulder is full contact plus .002-.0025 inches. But... you can bet yer bottom dollar they go a lot higher on the crush factor. Thats not crush as in bore crush, but shoulder crush/thread crush. IOW, if you were 24tpi One turn would move you 1/24th inch or just over 40 thousandths. Half a turn twenty thou, 1/4 turn... ten thou, 1/8 turn... five thou, and 1/16 turn or so, is your two and a half thousandths of an inch. So it goes solid about 1/16 turn from being lined up, then is crushed into place to line it up vertically.
(edit) I have no idea what the Ruger's tpi is... probably coarser than 24tpi. I just used that figure for easy in the head math at midnite. Its probably more like 16-18 tpi (guess).

The problem is, threads will distort as they're crushed, and the hollow insides (the bore) will also distort... not so much constrict, but... go wavy.
(edit) Plus the stretched tubing effect - constriction from that too.

The good news - it means NOTHNG in practical terms on a handgun. The bullet is under pressure and will expand to fill the space provided at that point in the barrel, its a no big deal thing.

Lead slugs... not the way to gauge it. You'd use a pin gauge, which are available in at least half thousandth increments. One will pass, one will not... etc... thats the size... between those two points.

Lapping is a finishing technique. Surface finish, not surface rework. If you tried to remove metal with lapping, you'd take forever, and you'd also wear the lands first, then the grooves - thats how it works.

The problem is all inside your noggin, as to how it should shoot. Putting .44 bullets on a pie plate at 200 yards is a real chore with a handgun.

[mr surveyor]

CJB.... you're the voice of knowledge I was "calling out":). Glad you caught the thread.

So, you're saying that the bullet re-expands in the barrel when it clears the constriction? That's a question by the way, not a statement. I was under the impression that once the bullet obturates just past the throat, and it then hits the restriction, there ain't much chance of it re-obturating? (question again).

Yeah, I forgot about the pin guages, I just remembered reading that one could actually "feel" the constriction (if present to any measureable degree) by slugging. Been reading too much lately.

I have one box of the 240 gr lswc's that I planned to stock up on, so I guess I'll watch for leading, as well as accuracy before I order a thousand. Those will be mostly range fodder, loaded with about 9-9.5 gr Unique.

Guess I'm getting as fidgity about wanting this gun to be a real shooter as a school girl getting dolled up on prom night. Not interested in 200 yard pie plates, but 30-50 yards from a braced position would be nice:)

Your opinion on fire lapping is to not fire lap?

surv

edti to add: this is one article that lead me to to thought of working on the SRH, if it showed signs of needing attention

http://www.gunblast.com/FerminGarza-Firelapping.htm

[CJB]

When the constriction is very close to the cylinder gap, as it is, there is still sufficiently high enough pressures to mush that bullet around quite a bit. It will re-expand. First... it may get smaller - or bigger - as it crosses the gap. The whacked to bore size at the beginning of the barrel, then the bore gets... wrinkly just a little... dont worry its damn near undetectable, and the bullet forgives the barrel and everything is smooth from that point forward.

Dont fire lap. They do that with new cut rifle barrels - target barrels - to get the tooling roughness off. Harry Pope never did, he preferred just shooting the gun, minimal HAND lapping by him.

You've got a SRH - great revolver - just... its a revolver. You're going to get revolver accuracy from it....and SRH's are very accurate. Much better at placing bullets than I am, for sure. A ncie 2.5x scope... and even then... from a rest... hit a clay bird at 100 yards. VERY hard to do. Shake, trigger, everything... the little ... very little... you'd see with a perfect and lapped bore... like wearin nothin but a condrum to stay dry in the rain.

[mr surveyor]

Thanks for your opinions. I think you convinced me to not waste my time... or the .001"+/- I'd be grinding off the lands. As long as I can put a slug at 25 yards "minute of sow" with the gun, that will be accurate enough.

Leading is the main thing I was trying to prevent, although I haven't personally shot any lead in the SRH yet. And, that may not even be an issue in the end. I'll be loading a box of .429's first, so if anything is going to lead the barrel, I'd expect them to do so. The bulk bullet order is on hold pending the experiment with the .429" swc's. I've got a buddy that probably has a small variety of .44 bullets in his inventory, so I may be able to get a handful of .430's and .431's to try before I order a thousand.

Thanks again.

surv

[muggsy]

+1 on everything that CJB said. Fire or hand lapping a barrell is for bench rest shooters who are trying to obtain sub 1/4 minute of angle groups with their rifles. Ain't fer handgunners.

[wyntrout]

Is that like measuring with a micrometer and cutting with a chainsaw?

I was gonna say that I believe I've seen on the Internet kits for fire lapping... and if I remember correctly, there was some kind of (maybe graduated) abrasive add-on or something involved.

Wynn:)

[TheTman]

I fire lapped a .357 using 38 special loads on a barrel that had some minor pitting inside, just to smooth out the rough spots. Accuracy increase was very minor at 25 yards.

[mr surveyor]

Is that like measuring with a micrometer and cutting with a chainsaw?

I was gonna say that I believe I've seen on the Internet kits for fire lapping... and if I remember correctly, there was some kind of (maybe graduated) abrasive add-on or something involved.

Wynn:)


yep, LBT is one company that sells bore slugs and their own fire lapping kits with bullets and lappinig compound ready to light load in your fire formed brass. CJB makes a good point about the possibility of taking too much metal off where you don't want to lose it. Still scratching my head on this one. I'll put the thought on hold now... I picked up my dies today, so I can load up a few 240 gr SWC's and look for leading and accuracy from the bench. I'm expecting leading though since the box of bullets that were given to me are sized to .429. I'll find out pretty soon.

[DeaconKC]

Firelapping has worked for me on some older rifles that showed very poor bores. Only one did not respond favorably, but that was a "sewer pipe" but it did make it much easier to clean. The LBT kit is an excellent way to go with good instructions.

[CJB]

Just totally un-needed on any hangun, except maybe silhouette open class stuff.

Places to make your revolver more accurate:

ABSOLUTELY make sure the crown is perfect. It must be absolutely square. There are tools to square it up while on the frame, and it can be relieved, once square, with a crowning ball. I've done the crowning ball... works great - as long as the crown is square.

The cylinder gap should also be absolutely square. There are tools for that too - but... just be careful or a trip back to Ruger for barrel setback will follow.

Cylinder face must be absolutely square - same cautions, but must be done on a complex setup - cant just lathe chuck it and say its good to go. The HOLES inside must be plum, not the outside...

Forcing cone in barrel can always be cleaned up - tools for that - long taper, smooth, etc.

Trigger - needs no saying

Getting the mechanics of the gun perfect, will go far far far... and farther... beyond any fire lapping.