Too little neck tension? Virgin Lapua Brass? Cratered Primers

[Straightshooter1]

I anneal every time and have run neck tension so light you can move the bullets by hand (that was not on purpose) with no sooting.

--Jerry

Ditto

And when I fired mine, I was hand feeding my bolt gun, a .308, and they performed . . . ok and no soot. If they're that loose, I wouldn't mag feed them nor use semi-auto platform.

 

[Straightshooter1]

I don't think jump affects pressure much but am not sure.

Jump will affect pressure to the extent that it's a function of seating depth. As one seats the bullet deeper to get a longer jumps, pressure increases as the case's interior volume for powder is being decreased.

 

[LCazador]

Jump will affect pressure to the extent that it's a function of seating depth. As one seats the bullet deeper to get a longer jumps, pressure increases as the case's interior volume for powder is being decreased.

This is correct but the force of compaction is also going to change the seating depth by forcing the bullet out. Also as you seat further out into the lands the additional force required to chamber the round will push the bullet back into the case and change the seating depth as well as the interior volume of the case.

 

[CA_Shooter]

I wanted to give an update for anyone that may have this issue in the future and may find this thread useful. Thank you everyone for the thoughtful replies.

I did another round of testing today and did not have any cratered primers. I had 1 or 2 with a very very slight ring that you can see if you squint.

What I changed this time vs the last when I was cratering primers:

Craters:
•Virgin Lapua Brass, which is very short
•extremely light neck tension. 5‐10 PSI with my arbor press
•jumped to .0200

Today, no craters:
•once fired lapua brass, bump sized to .002. I only used brass that was bump sized .002 under my chamber. Brass that didn't grow to this size was not used for testing today.
•tighter neck tension. 25-40 PSI with my arbor press
•jumped to .0790

It seems that what was causing the craters was the virgin lapua brass because it had a lot of room to grow and the cases that cratered grew the entire size of my chamber on the first firing.

 

[CA_Shooter]

I want to give a final update for this thread. The issue turned out to be that the firing pin hole on the bolt was too big, which was cratering and piercing primers.

Big thanks to @carlsbad for fixing my bolt. Issue is now gone after he bushed the bolt. Here is an image of primers shot today. None cratered or pierced