Concave Primers...?

[ma smith]

Never seen one of these before, got two last night. Chalk this up to you "learn something new everyday." This was from the "set aside" pile from my lmatch ammo. Chrono says -20 fps beglow mean (both witin 1 fps). sSo the good news is the process worked. Bad news is I didn't take detailed notes. Curious to know if folks here have experience with this at all.

Pic from accurate shooter (not mine, but it looks same....)

 

[Haney]

Is your powder charge on the low end ? This is common with reduced loads .

 

[918v]

That’s a pierced primer. It’s concave because the firing pin dented it and the pressure that normally fills out the dent blew out the pierced hole.

 

[Rocketvapor]

Remove primer, remove anvil, photo.

 

[Haney]

That is not the OP's primer , he stated his is concaved .

 

[redbullitt]

Have had lots of low pressure stuff leave a dented or concave primer. Agree with above about maybe that'd be the issue?

Load data would be helpful