Had a Couple of 9mm Key Holes Today

Random sampling of bullets from the same lot=355"-.355.5"

Not determinative, but an indicator bullets not the problem, right?
With enough pressure / propellant dynamics bullets can 'bump up' and work better, but something else can come into play even with bullets sized above nominal groove diameter - Taper crimping / factory crimp die crimping after seating, where the case and bullet are 'squeezed' to a certain point, the case springs back but the bullet is left very much undersized. Worst I have seen this was with Lee tumble lube type bullets, but any can fall to this. Going to be really hard to get any accuracy from say a .353" bullet driven down a .3575 GD barrel, esp at modest pressures.
 
Were the cases the same headstamp? Over tapercrimping is the most common cause.
Yep all Winchester from my 17 month test--36/37 firings each. i only "kiss" to remove any flare which is seldom evident. Most could be used without crimp. Undersized & never have identified set back.

Edit: kind of clunky written--I don't put much crimp at all is bottom line.
 
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Great comments

Large paper target stapled to cardboard backing and every few mags a new shoot n see stick on four inch center. So, no more than say 15 shots visible on center of target.

Keyholes were off the stick on by an inch or so or more.

Hadn’t thought about cracked case & beretta combo.
This concern is exactly what I'm afraid of using xtreme plated 220gr. through my suppressed CMMG Banshee 10mm
2500$ setup and one unstable bullet and disaster. Even if I test 50 rounds without the suppressor, do I fully know it's safe?
 
This concern is exactly what I'm afraid of using xtreme plated 220gr. through my suppressed CMMG Banshee 10mm
2500$ setup and one unstable bullet and disaster. Even if I test 50 rounds without the suppressor, do I fully know it's safe?
I don’t know anything about suppressors and hadn’t even thought about the consequences of a tumbling bullet.
 
I don’t know anything about suppressors and hadn’t even thought about the consequences of a tumbling bullet.
You would think the bullet would be a ways from the muzzle before it started to tumble….??

Still….. a chance that will be taken if shooting suppressed….

I have sent 1000’s downrange thru the same(similar) setup as @Palladan44 operates.. no issues with plated and coated 220grainers….but I have found a recipe that utilizes a fairly full case of powder that is slightly below max charge….

YMMV, of course :) …..
 
Ya know you might have had a couple undersized bullets slip in your pile. Might have been lighter as well. Hard to find a cause after they have been shot and no other of the usual culprits show their heads. Might have been some light charges but you know your pistol well enough by now if any light recoil or corrpsponding heavy recoil due to propellant bridging in a few rounds.
I really don't like not being able to figure out the problem with something. Especially with reloading and the ability to explode things.
 
Hard to find a cause after they have been shot and no other of the usual culprits show their heads.
Yep, like this, never before, never since, just the one, left guessing what happened. With a very popular for 300 BLK bullet, the Speer TNT. I've never loaded them in Blackout again, but people do all the time. Set back is my guess, but dunno for sure.......

Blown Primer 300 BLK Pic 1.JPG
 
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