Pistol: S&W M&P40 4.25"
Ammo: Federal Premium HST 180gr 40S&W, nickel case

I was cycling my carry rounds out of my primary mag (the one in the S&W M&P40, not the spare on the belt), and I noticed quite a few rounds had case deformation. The one pictured has a ring all the way around the circumference.  The others are on their way to similar results.  I haven't put a caliper to them yet, but I bet they are slightly shorter OAL than factory. These were all a few down in the magazine, not the top round or from the chamber.

Attached File


Any idea what would cause this?  I have no plans to fire these rounds, too worried about overpressure with the already hot cartridge. Just trying to figure out why this is happening.

Thanks.  I had tried a Google search, but nothing relevant came up (probably because I didn't exactly know what to call it.)

I did put a caliper to the one round that had the ring all the way around.  It came out to 1.123", while a fresh-from-the-box round came in at 1.126".  So it has shrank about 0.003" in OAL.

Looks like this problem has existed for over 9 years now, and it is still doing it.  Federal must either:
1.) Not think it is at all a problem
2.) Have no idea how it is happening, and have no solution.

Hmmmm.....

How often are you cycling rounds?

I usually empty and clean the mags and rounds every 30-40 days, although it may have been a bit longer on this cycle.  They seem to collect lint and dust pretty easily, so I try to keep them clean.  Every 6 months, I shoot the carried ammo and replace it with fresh rounds.  I try to avoid chambering the same round more than 2 times.

Federal must be having issues in their HST QC department. I ordered 200 rounds of 9mm 124gr HST and all the brass case mouths still had quite a bit of flare from the loading process. I ran them through my Dillon to finish the taper crimp.

I've had cases crease similarly to that with 230 grain HST that had been loaded in P220 magazines for a while.

I believe it happens because the brass is soft and the pressure of the loaded bullets on the cases crease it but I can't say for sure.

ETA: when this occurs I fire the ammo at the range without incident.

I carry 9mm 147 HSTs.  I have observed the same occasionally with long term carry ammo.  When I see I remove and shoot next range trip.  I've not had a problem with one going off yet.

OP, this exact same thing happens to me as Federal HST is my go to carry load in 9, .40, and .45acp... It's usually the 2nd or 3rd and even the 4th round in the magazine that looks just like the round you pictured. I think absolutely nothing of it as every time I've shot the ones that looked like that they always fed and always fired accurately without fail. I keep them in my magazines now and don't even separate them to shoot the next range trip as it's only a cosmetic issue from my experience. Should it happen, probably not. Am I going to dispose of them or stop carrying HST's, hell no! They are proved Self Defense rounds!