Bump up.

[muffett.2008]

I know this pic is a bit late, I recollect a posting before in relation to the ability of boat tails to seal the bore versus flat base projectiles.

I did an article on one of the forums years ago, but know with being stuck in the big wet, with nothing to do and limited info I came across this pic showing base bump on a 2 groove barrel, the seal created by the bump above the boat tail and the extrusion of the lands.

If the boat tail projectile is pushed above 2000fps, you will get adequate sealing.
Attachment 113986

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