Folks,

-Kimber ultra carry 45 with a factory kimpro tac-mag

- Once in a while fun will strip a round, get it within about 1/4” of fully into battery and then hang up.

- if I drop the magazine it then goes into into battery.

- inspection of next round in line in the magazine shows that it slid forward a little bit.

I think that the “next” round is getting pulled forward in the magazine a little bit and creating a sort of obstruction which binds up the current round as it is trying to go into battery.

Any likely root cause, or am I just going to have to play with mags until I find one that works?

I hand cycled a few different mags worth of ammunition and found that my Springfield GI mags with traditional followers did not exhibit this. They cycled really smoothly by hand.

I observed that I can depress the nose of the follower really easily on these Springfield mags, and that they also have a little nub on the follower surface. I’m guessing that either the follower makes it easier for the slide and feeding cartridge to ride over the next cartridge or that the nub helps keep the next cartridge from sliding forward in the magazine.

Extractor could be too tight, series 2 pushrod and firing pin block could be binding, recoil spring could be worn, bullet may be impacting frame first before the feed ramp and causing the slide to loose velocity, limp wristing could cause the slide to lose velocity, lack or improper lubrication.

If its new / under a year old have kimber take it back and rework it. No sense blowing your ammo trying to troubleshoot problems that they put out.

I was able to duplicate the failure mode by hand cycling the weapon.

What I found was that the bottom edge of the breech face was not sufficiently chamfered and the sharp edge was digging into my brass. That’s why it closed into battery when I would drop the mag.

Pics of gouged brass:
Brass gouged from multiple hand cyclings

I compared the chamfer to my fully reliable stainless TLE and replicated the geometry, stoning the chamfer to extend a little further back and breaking the sharp edge where the chamfer transitions to the slide bottom.

TLE chamfer

New ultra carry chamfer (enlarged)

Hand cycling now permits smooth feeding of rounds, even when I cycle it slowly. I didn’t really change the overall depth of the chamfer on the breech face surface, so it shouldn’t affect how it strips the next round. I tried to “rip” the slide as fast as I could to induce a failure to strip and it seems just fine.

I will update if my next range session is a dud but it appears that the resolution was pretty straightforward.

ETA: my first hundred rounds with Winchester white box were flawless. These failures were with federal champion. I am guessing the federal must have had softer brass that would let the sharp edge dig in deeper.

Glad to hear it was something relatively simple.

If it wasn’t something so easy I would have considered sending it back, but I have limited faith in Kimber customer service.

Call me a sucker but I do like Kimber aesthetics and feature sets. I Can see how someone with limited mechanical aptitude would be really upset - not like its rocket science to fix what I fixed but your average buyer isn’t going to want to tinker and troubleshoot.