CM45 magazine mod.

[jrm189]

I purchased a new Kahr CM45. I followed the break in rules that Kahr recommends. Using slide stop to chamber first round, and used 230gr FMJ for the first 200 rounds and expected nothing except an occasional jam until I got it broke it. After 80 rounds and 3 failures, it's been smooth for around 450 rounds. I'm a double action guy, and it gets no better than this trigger.
I have 2 problems with the firearm. One is the trigger reach is a bit short for my tastes. The other is the 5+1 capacity.
I know other folks have discussed this mod to increase the standard mag capacity to 6+1, and I just wanted to provide a little test results for anyone interested in doing the mod.
I disassembled the mag and cut the spring one coil at a time until I could fit a 6th round in the magazine. I chambered one and loaded the mag fully and found there was too much resistance between the bottom of the slide and the top of the 6th round in the magazine. I pulled the mag back apart and cut one more coil. And tried the process an and everything worked very smoothly. Even slide lock back on empty. After running the gun around 30 times out in the backyard as I will carry 6+1, everything ran perfectly.
I do understand that my spring longevity has been sacrificed, but spring follower kits are inexpensive and I don't mind replacing for the extra round.

Just wanted to give feedback in the event that anyone was looking to try it.
I absolutely love this pistol.
Jrm189

[ScottM]

Nice! Really appreciate the write up.

[yqtszhj]

Thanks for sharing that info. Do you know about how many coils you removed?

[CJB]

One thing to be very careful of....is cartridge rise time due to the shorter - less tensioned - spring. As you noted, not right now, but perhaps later down the road, you might experience some slow rising cartridges, the result would be... I dunno. Depends on other factors like bullet nose shape and such. Cutting a mag spring could be a long fuse to a problem, especially on the last shot or two from the magazine.

[jrm189]

I'm not sure how many. I'm out of town but can take a picture/count of what's left when I get home.

CJB, you are correct. Double taps function fine. I shoot at least once a week, and should notice any considerable change/wear. This ends up on my nightstand at night and in have a factory extended mag that sits loaded. The mag with the cut spring gets unloaded when I get home to extend the life.
As I said, I'll let you know the remaining spring length.

[jrm189]

And also CJB, as finicky as Kahr pistols can be, part of me wonders if the resistance between the top round in the mag and the bottom of the slide with stock spring tension is so great it causes short cycles, or failures to go fully into battery.
Again, I'm not saying this fixes that issue, but I will sat mine goes fully into battery when using the slingshot method now, whereas before, it would hang 1 out of 4 times. YMMV.

[yqtszhj]

And also CJB, as finicky as Kahr pistols can be, part of me wonders if the resistance between the top round in the mag and the bottom of the slide with stock spring tension is so great it causes short cycles, or failures to go fully into battery.
Again, I'm not saying this fixes that issue, but I will sat mine goes fully into battery when using the slingshot method now, whereas before, it would hang 1 out of 4 times. YMMV.

Fyi, that slingshot working better improves over time anyway i have found. It also seems to slingshot on the .45's better than the 9mm's at least with my pistols. Funny how rounds down range seems to make things smooth out too. Glad yours is working well for you.

[ScottM]

Jrm189, your 6+1 mod using a stock mag size is potentially kind of a big deal if it holds up.

[CJB]

And also CJB, as finicky as Kahr pistols can be, part of me wonders if the resistance between the top round in the mag and the bottom of the slide with stock spring tension is so great it causes short cycles, or failures to go fully into battery.
Again, I'm not saying this fixes that issue, but I will sat mine goes fully into battery when using the slingshot method now, whereas before, it would hang 1 out of 4 times. YMMV.

Not sayin there's not enough overkill in things to work ok, it might!

On the other hand.... there is precious little overtravel of the breechface past the point it needs to pickup a new round. As things break in, the recoil spring will weaken (its designed to). Things will speed up! The mag spring will be a little weaker, not too much with use. But, a little weaker here, a little faster there.... less ammo tolerant, less hold tolerant, etc. Just keep an eye on it.

I think I'd have used the P45/CM45 mag, but I like the idea. For years Colt said 7 rounds, thats it. Now they got 8, who'da guessed in 1918, or 1941?

[jrm189]

I'm no gunsmith (yet, anyways) but I took apart my 1911 mags and compared the spring with the Kahr mag spring and the Kahr spring has super tight coils. I wonder if a heavier spring with less number of coils could get the job done as well as stock. The problem comes when the coils stack in the bottom, and it seems like a lot of wasted space. Now I know my 1911 has a lot more tolerance for next round pick up at breech face, but still seems wasteful on the 5 rounder.
But the recoil spring weakening should allow more "feed time" as it's not in as big of a hurry mechanically.
I'll keep you posted on if/when I have feed failures.

[CJB]

The cartrige starts to rise as the breech face clears the back of the magazine (or rim of the cartridge actually). On its rearward travel, the slide will be moving faster. As you noted, on the forward travel, slower from spring tension alone. However, I think you'll see that there is considerable "bounce" of the slide as it makes it rearward stop.

In years past, I shot the 1911 with no recoil spring to see what would happen. You damn near get a chambered round. Not quite. Partially stripped to half stripped from the magazine. Thats how much bounce you'll see.

We'd have to consider a LOT of things to calculate it, but I think its safe to say with weaker springs, in that portion of the travel, you'll get less rise time available.

[jrm189]

That's good info. Thanks for sharing. I'm hoping there is enough tolerance around for my change to function for a while. Magazines are designed to function for a time before needing to be replaced so I'm hoping to have only cut the life in half.

[ulflyer]

Some years ago a gun mag ran an article about a WWII 1911 mag the guy brought back from the war and had been laying in his drawer for something like 50 years, fully loaded with seven rounds. They ran all seven successfully thru a 1911 pistol. Says something
about mag springs holding up. However, I realize our fussy Kahrs are a different breed
from the 1911's and far less tolerant.

[Bill K]

Interesting mod. Thanks for sharing.

Be nice if someone like Wolff made a drop in spring for the mag that would accomplish the same increased capacity with no spring tension or life down side.

[tooltruckguy]

Just found this thread. I just bought a CM45. Did you ever figure out how many coils you cut off the mag spring?

Thanks.

[DJK11]

Thing is my PM45 5 and 6 round mags have the same springs. So one would think some Wolff extra power universal 1911 mag springs should work. Just trim them to the correct length. Looks like an order for springs is coming up.

[MACVSOG]

Thanks for the info.

[Baklash]

Just wondering about howzit going with your mag spring modification. It's been around 9 months since you made the mod and I would appreciate an update. You could be onto something here, whether it be cutting off coils or finding shorter springs, etc. Just about everybody would be in favor of an extra round in these small guns once long term results are evaluated. BTW, thanks for the original post.