Reloading .303 British : Effect of Primer Selection on Muzzle Velocity

Now, for the chrono and group/score results yesterday with the T. 

I shot two basic loads, with two different cartridge OAL as follows:

1) 40.0 gr Varget, 3.05 inch OAL

2) 40.3 gr Varget, 3.05 inch OAL

3) 40.3 gr Varget, 3.07 inch OAL

All loads used a neck sized PPU Case, WLR Primer and 174 gr Sierra MatchKing.

Temp varied from 49 to 62 deg. Clear skies, winds 2-4 mph from 6 O’Clock.

All groups are 10 shots, resting the fore-end on a sand bag per CMP Vintage Sniper Rules. Rifle held firmly into shoulder, no sling.

Here was the 300 yard group on the US NRA Short Range Target. I’ve shot better (smaller group), but a score of 100 is as good as it gets.  

The column marked “C-C (MOA)” is the group extreme spread in minutes of angle measured from bullet centers of the widest two shots. Some of these groups would have been smaller because I made scope elevation and windage changes to move the group to the center of the target. In general, the rifle was grouping under 2 MOA during this test. 

Groups 1 & 2 with the Mk I Aperture Sight

Groups 3 thru 9 with No. 32 Scope

Groups 1 thru 4 -    Load 1), 40.0 gr Varget

Groups 5, 7 and 9 - Load 2), 40.3 gr Varget, 3.05” OAL

Groups 6 & 8 -        Load 3), 40.3 gr Varget, 3.07” OAL

1) Velocity ES and SD does not settle down until about 50 rounds are fired.  Even longer if it has been cleaned to bare steel. 

2) No obvious difference between 3.05 and 3.07 seating depths, slightly lower mean velocity for 3.07.

3) Velocity ES begin to creep up after 60 rounds, but not significantly and had no adverse effect on score. 

4) The rough grooves are likely the cause of large velocity spreads and consequently large group extreme center to center spreads.  Carbon fouling mitigates this. 

5) The grouping capacity of this rifle and ammunition is around 1.5 to 2 MOA if fired for smallest size group rather than for score (i.e. not making any sight adjustments).

6) This rifle shoots well enough to win CMP Vintage Sniper Matches if I do my part.

I suspect Shamu is right, there may be a sweet spot with this barrel in terms of how much fouling shoots best. For the next while, I will only do a “light clean” after shooting; a few patches wet with Hoppes 9 and Kroil mix, let soak overnight and patch out dry next day. Store muzzle down with bore wet with the Hoppes 9/Kroil mix.