G34 loosing OAL

[Chapo]

I am testing a load for 9mm major. Ive been doing the plunk test and found perfect OAL of 1.345.  However, when I place round(no primer round) in the magazine, chamber it and ejected it, when I Check the OAL again comes out shorter.  I've adjusted for a firm crimp but when I check the OAL after round is ejected I notice the OAL is shorter.  Is this normal?

[GrumpyOne]

Too much crimp. How much shorter are they getting?

[Chapo]

I am sorry my OAL is 1.145.  It goes down to about 1.40

[GrumpyOne]

When you re-chamber the same round, does it get even shorter?

[Chapo]

I adjusted the crimp so that now no matter how many times a chamber the dummy round it remains the same IAL

[GrumpyOne]

Over crimping has the opposite effect than what one would think. All you want to do is remove the bell/flair that was put into the case. Measure the case wall thickness, multiply that by 2, then add your bullet diameter, that should be your crimp. EG: case wall =.011 × 2 = .022 + .355 = .377 crimp.

[Chapo]

Thanks.  I think I'm good now

[nhyrum]

Too much flair can do the same thing.

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[4n2t0]

14 hours ago, Chapo said:

I think I'm good now

 

Probably not but you seem content just crimping the s#!t out of your rounds.

 

FYI...Sizing prevents setback.

[nhyrum]

 
Probably not but you seem content just crimping the s#!t out of your rounds.
 
FYI...Sizing prevents setback.

I agree. You don't want to over crimp. It will actually swage the bullet down. Flare just enough so the bullet sits in the case just firm enough to not fall out on the press, and crimp just hard enough to remove that flare. That's it for stuff like 9. The case indexes in the chamber off the case mouth for 9mm. If it's crimped too hard, it's got nothing to index off of

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