Author: britrifles
Subject: Case Neck Concentricity
Posted: June 16 2023 at 10:42am
I pulled out some of my Dominion Arsenal 1951 Mk 7z ammunition that was made for the 1952 (and later) DCRA Matches and checked bullet runout. It is remarkably consistent, .002 inch max was measured in 10 sample rounds. This ammo is still remarkably accurate, the most accurate .303 Arsenal loaded ammunition I have fired in the .303. The sample round below was typical, only .001 inch bullet runout.
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Subject: Case Neck Concentricity
Posted: June 16 2023 at 10:42am
I pulled out some of my Dominion Arsenal 1951 Mk 7z ammunition that was made for the 1952 (and later) DCRA Matches and checked bullet runout. It is remarkably consistent, .002 inch max was measured in 10 sample rounds. This ammo is still remarkably accurate, the most accurate .303 Arsenal loaded ammunition I have fired in the .303. The sample round below was typical, only .001 inch bullet runout.
I checked the five remaining handloads that I shot last weekend at the D-Day Match that I assembled with new PPU cases and 174 SMKs seated with my Lee die and they measured .004 to .009 inches. I’m not impressed, not sure what the problem is here as the case neck runout measured much better. This might explain why I dropped 3 points in prone slow fire compared to my usual score at the match with necked sized cases.
Loaded cartridges assembled my with cases neck sized in Lee Collet die neck were much better. Typically .002 to .003 inches of bullet runout. The largest I measured was .004.
From now on, I will only use cases neck sized from my Lee collet die for matches. I’ve also got to check bullet runout once I load cartridges from cases that are partial length sized on my new Forrester Benchrest sizing die. I’m hoping they will be as good as the neck sized cases.
This only confirms what I suspected all along, that ammunition loaded with new cases, or cases that I had been full or partial length resized were just not as accurate as my loads with cases neck sized in my Lee collet die. And I believe the reason is bullet runout. If the bullet does not enter the throat concentric with the bore, it remains off center as it travels down the bore. I think the deep groove rifling in the .303 exacerbates this (groove diameters are typically .314 inches or more).