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Got to go to the range this weekend to test a couple changes made to the 20" 7.62x39USA......I had PTG make me a new chamber reamer to try a couple new ideas.....I moved the shoulder forward .050", opened the neck up .001" and added .003" taper to the neck....The gas port that I had been trying was .093" and the rifle cycled ok but was a little slugish and would fail to lock open every once and a while on the last round with less than 25gr of 1680......
I went to the range with a bunch of 125 TNT's with 25gr of 1680, my drill press and numbered bits.....opened the gas port up .002 to .003 at a time firing 10 rounds between.....took a little time but ended up at .102 with very reliable cycling.....now that the shoulder is moved forward .050" I can now fit a little over 26gr of 1680 in fire formed brass....with more powder and a bigger gas port it brings the adjustable gas block back to use other than wide open....also noticed that opening the gas port around .010" took about 80 fps off the top-end of the 25gr loads now clocking around 2450.....
I can't say enough good about the 20" 1:12 Noveske on this rifle, rapid fire (10 rounds in about 8 seconds) from a bi-pod at 100 yards printed a group that could be covered with a quarter....very happy, thanks John....
now to work on load development for the 16"....hopefully this weekend...
kurtz
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