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SL1 · July 7, 2012, 10:05 AM

I calculated pressure changes for a 0.003" increase in seating depth for two powders under a 200 gr lead FN bullet in the .45 ACP cartridge, starting at 21,000 psi ("+P" pressure limit for .45 ACP). For the faster powder I got a 70 psi increase, and for the slower powder, I got a 182 psi increase. (I was expecting the opposite for the increases, but who am I to argue with QuickLOAD.)

Anyway, I think this showes that the bullet length variations that you measured are inconsequential. Variations of a few thousand psi from shot-to-shot are typical on pressure measuring systems with good quality ammo.

Also, keep in mind that sprue marks on the bases of cast bullets can affect length measurements by a greater percertage than the actual percent change in the volume of the bullet inside the case. A 0.003" ridge or bump on the bullet base is usually inconsequential to accuracy as well as to pressure.

SL1

July 7, 2012, 10:05 AM	#7
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	Using QuickLOAD I calculated pressure changes for a 0.003" increase in seating depth for two powders under a 200 gr lead FN bullet in the .45 ACP cartridge, starting at 21,000 psi ("+P" pressure limit for .45 ACP). For the faster powder I got a 70 psi increase, and for the slower powder, I got a 182 psi increase. (I was expecting the opposite for the increases, but who am I to argue with QuickLOAD.) Anyway, I think this showes that the bullet length variations that you measured are inconsequential. Variations of a few thousand psi from shot-to-shot are typical on pressure measuring systems with good quality ammo. Also, keep in mind that sprue marks on the bases of cast bullets can affect length measurements by a greater percertage than the actual percent change in the volume of the bullet inside the case. A 0.003" ridge or bump on the bullet base is usually inconsequential to accuracy as well as to pressure. SL1