Monday, March 24, 2014

4095 redux

Once more dear friends, into the breach, this time testing the larger diameter assembly pins and Power Pistol powder.

The oversized pins really help stabilizing the sights and getting group sizes down in the 3-4 MOA range. This with only replacing the rear pin too. The assembly pins on the newer stocks with the swinging latches are enough undersized to add some 2 MOA to the base accuracy of the gun using the iron sights, and 6 MOA if you're using some sort of optics which rely exclusively on the bolt shroud for support and stability. I'm using a 7/32" dowel pin in the rearmost hole, the front hole proving to be just a bit sticky. Next time.

I tried Power Pistol powder as it's a rather slow-burning type on the theory that it might favor the longer barrel on the carbine. Available bullets were 155 gr Barry's plated. Sure enough:

Bullet    Source    pistol        Amount    Velo        
155    Me       8.1    8.3     8.7     8.9
               1594    1617    2267    1669
               1649    1656    2114    2231
               1616    1672    1687    2158
               1690    1694    1453    1695
               1677    1656    2221    1698
               1645.2    1659    1948.4    1890.2
       Var+/-        44.8    35    318.6    340.8
Nice start at 1645 and 1652 fps for the lighter loads. Impressive numbers, 2267 and 2231 for the heavier loads although the variation in velocity over 5 rounds was appalling. I suspect that at the higher speeds the plating was disintegrating from the bullets. The gun is noticeably more accurate using 180 gr jacketed bullets anyway and the combination of thin plating and light weight isn't helping. I may need to get a pound of Power Pistol and some real jacketed bullets for the next go-round.

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