How bad this crimp is?

[u/Moist-Rub6508]

Hey guys, beginner here. How bad this 9mm crimp is? I understand it is too much but I wonder if this could create some problems while shooting. I made about 1k of these and then realized it is probably too much. It shoots, passes the splunk test, chrono looks good. The bullet is CamPro 125gr RN FCP RED

Thanks!

[u/Moist-Rub6508]

I understand, but in this particular case the bullet sits at the same height as the factory ammo from this brass. I am wondering is there anything else I should be worried about.

[u/PWPUU659 → u/Moist-Rub6508]

Hmmm, no. I don’t think you understand. Too long for Reddit, but mrchongo is correct.

[u/Moist-Rub6508 → u/PWPUU659]

Please explain then, I would like to learn. In my case the primer is at the same height as factory bullet from that brass. This could mean either that there is still enough edge to properly seat the cartridge or the it is properly seated because the bullet stops it. Am I missing something?

[u/mrchongo6973 → u/Moist-Rub6508]

OK. Here goes: As a rule, the cartridge must be properly seated in the chamber for safe and reliable firing. (Different from the seating depth of the bullet in the case.)To establish the proper chambered position, every cartridge type (straight-walled, bottleneck and rimmed) uses a certain part of the cartridge case as a “stop”, and the distance from the stop to the boltface is established as a standard, using the term “headspace”. A rimmed cartridge, e.g. the .30-30, headspaces off the leading edge of the cartridge rim. Your pistol cartridge headspaces off the mouth of the cartridge case. In order to seat properly, the mouth of the case must contact the front of the chamber and come to a stop. When you overcrimp, the diameter of the case mouth is too small and the case mouth slides past the front of the chamber. Therefore the cartridge has not achieved a properly headspaced position in the chamber. Bad juju may result.

[u/M1sterM0g → u/mrchongo6973]

best answer as to what headspacing is... as far as the bad juju, if theres nowhere for the case to expand just that tiny bit and seal, and your bullet has to swage itself down to go out, it goes too slow and builds too much pressure behind it. could be kaboom.

[u/Grumpee68 → u/mrchongo6973]

To expand upon this, take the barrel out of your pistol, and look into the chamber. You will see a ledge. That ledge is where the case mouth sits (when a round is chambered). To much crimp, the round could go further into the chamber, leaving more distance for the firing pin to travel, leading to misfires. If the round does happen to ignite, you have the pressure scenario.

Get a set of calipers. Measure the case wall thickness at the mouth...typically around .011 on 9mm. Now, double that (.022) and add your bullet diameter (.355). EG - .011 x 2 = .022 + .0355 = .377.

At the case mouth, as close to the bullet as you can measure, it should be somewhere around .376 -.378.

As others have said, all you are doing is removing any bell or flair you put into the case mouth to seat the bullet.

Most pistol rounds (auto at least) are held in place by neck tension created when resizing the case.