9mm CBC brass reject rate?

View · by **andrewP** on Fri Mar 27, 2015 3:49 pm

I loaded up a small batch (~250 rounds) of 9mm this morning (124gr Montana Gold JHP @ 1.075" OAL, mixed brass), and when I chamber checked them this afternoon, 11 failed the "plunk" test. I don't usually get anywhere near that high of a reject rate, but that wasn't what really surprised me. Of the 11 rejects, *10* were CBC cases.

While anecdote != data, it does seem like something goofy is going on. While I'm not ready to start tossing all CBC cases, I think I might segregate them to load separately and experiment with.

Has anybody else had a similar experience?

View · by **wrench** on Sat Mar 28, 2015 7:43 am

I also have issues with CBC brass in 9mm. It seems to work OK when I'm loading jacketed bullets, but when I load my larger diameter cast projectiles, I get a large percentage that fail the case gauge.
I just sort them out, and don't use them anymore for cast reloads.
Brass walls thicker maybe? Stiffer brass?

View · by **Ron Burgundy** on Sat Mar 28, 2015 2:52 pm

Same for me with CBC and 147 gr Montana Gold CMJ at 1.135. I just set CBC aside for now.

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View · by **andrewP** on Sat Mar 28, 2015 3:38 pm

Well, good to know that I'm not alone, anyway. I notice that the "reject" rounds do have a visible "coke bottle" effect that appears to indicate where the base of the bullet is. Perhaps it's the flat base of the JHP rounds and having to seat them fairly deep in order to pass the plunk test in my Walther combining to create a bit of a bulge in the brass at that point. Walthers, much like CZs, tend to have somewhat tighter than average chambers, so that could be the cause of my issue, as well. Either way, I guess I'll just watch for that headstamp and set them aside for now. Maybe if at a later date I end up loading some round nose bullets that don't have to be seated as deeply (I've loaded Berry's plated round nose out to 1.15 without issue), I'll try using them again.

View · by **OldmanFCSA** on Sat Mar 28, 2015 7:47 pm

Not 100% sure, but if you section a case you may find the wall is quite thicker if seated deeper than the original projectile was seated. It may be their method of controlling bullet setback.

View · by **andrewP** on Sun Mar 29, 2015 12:43 am

That's a good thought, which would easily explain why it's so clear where the base of the projectile is in the ones that failed the plunk test. Now if I could just remember where I put that hacksaw. I know it's *somewhere* in the garage.