megalomaniac
Well-Known Member
Bought a new factory Chriatenson Arms Ridgeline FFT in 7mm PRC a few weeks ago. Loaded up 47 factory 2nds 150g NBTs with a middle of the road powder charge of Re22 for bbl break in (box of 50 Hornady brass, pitched 3 right away due to extreme weight variances from mean).
Broke in the bbl with the shoot, clean... shoot 2, clean... shoot 3, clean.. shoot 4, clean... then shoot 5 and clean in between 5 shot strings until I finished off 40 rounds. Only going 2800fps average, book says they should have been closer to 3000 fps. No pressure signs, but one piece of brass during the break in had a slightly stick bolt lift and ejector marks.
Annealed the brass, left the 1 with ejector marks off to the side, then resized bumping the shoulder back 0.003in. Then switched to the 175 ELD-Xs and Re 25 to find optimum charge. Started at 66.0g working up to 68.7g in 0.3g increments (book max is 68.4g). Seated all bullets 0.020 off jam. Neck tension felt equal between all rounds, and seating them was butter smooth.
Shot the first 9 and found what I think is the optimum charge at 67.5g, but only going 2829fps (book says should be around 2950). Problem is, I was getting erratic pressure signs... see image.. light ejector marks at 66.9, but not at 67.2. Light ejector marks at 67.5, but not at 67.8, nor 68.1. Heavy ejector marks and sticky bolt at 68.4 (book max). Did not shoot the 68.7g load.
Group seemed to settle down to around 1in around the 67.5 mark as well (0.9in at 150y).
Plan was to take the optimum charge, then start varying seating depths in 0.005in increments to fine tune. But I'm confused by the erratic pressure signs... and also very disappointed I'm getting on average 125fps slower velocities per charge than book. Granted, I have a 22in bbl, and book test bbl was 24in. But I was figuring a loss of 50 to 60 fps, not 125.
Any thoughts on the erratic pressure? I would have thought headspace, but all base to shoulder lengths were measured with a headspace comparator after resizing. Unfired factory brass measures 0.008 less than my chamber, and I didn't overwork the shoulder, just set it back 0.003.
20 thousandths off jam should have kept me off the lands, even if there were bullet to bullet variances in location of ojive, and none of the rounds felt like bullet was touching the lands when I closed the bolt.
Now I'm not really sure where to go from here... just suck it up and accept around 2825fps from the 175s and current powder? Still a little room in the case... but with a 22in bbl, I'm not sure switching to a slower burning powder like magpro, imr 7977, or retumbo which should fill the case completely will be completely burned in a shorter barrel.
Maybe try VV N565? Supposed to have a little more velocity with the double base burn rate, esp in a short barrel?
Hate to do it, but I may have to actually buy a box of factory ammo from Hornady in 7prc to compare.
Broke in the bbl with the shoot, clean... shoot 2, clean... shoot 3, clean.. shoot 4, clean... then shoot 5 and clean in between 5 shot strings until I finished off 40 rounds. Only going 2800fps average, book says they should have been closer to 3000 fps. No pressure signs, but one piece of brass during the break in had a slightly stick bolt lift and ejector marks.
Annealed the brass, left the 1 with ejector marks off to the side, then resized bumping the shoulder back 0.003in. Then switched to the 175 ELD-Xs and Re 25 to find optimum charge. Started at 66.0g working up to 68.7g in 0.3g increments (book max is 68.4g). Seated all bullets 0.020 off jam. Neck tension felt equal between all rounds, and seating them was butter smooth.
Shot the first 9 and found what I think is the optimum charge at 67.5g, but only going 2829fps (book says should be around 2950). Problem is, I was getting erratic pressure signs... see image.. light ejector marks at 66.9, but not at 67.2. Light ejector marks at 67.5, but not at 67.8, nor 68.1. Heavy ejector marks and sticky bolt at 68.4 (book max). Did not shoot the 68.7g load.
Group seemed to settle down to around 1in around the 67.5 mark as well (0.9in at 150y).
Plan was to take the optimum charge, then start varying seating depths in 0.005in increments to fine tune. But I'm confused by the erratic pressure signs... and also very disappointed I'm getting on average 125fps slower velocities per charge than book. Granted, I have a 22in bbl, and book test bbl was 24in. But I was figuring a loss of 50 to 60 fps, not 125.
Any thoughts on the erratic pressure? I would have thought headspace, but all base to shoulder lengths were measured with a headspace comparator after resizing. Unfired factory brass measures 0.008 less than my chamber, and I didn't overwork the shoulder, just set it back 0.003.
20 thousandths off jam should have kept me off the lands, even if there were bullet to bullet variances in location of ojive, and none of the rounds felt like bullet was touching the lands when I closed the bolt.
Now I'm not really sure where to go from here... just suck it up and accept around 2825fps from the 175s and current powder? Still a little room in the case... but with a 22in bbl, I'm not sure switching to a slower burning powder like magpro, imr 7977, or retumbo which should fill the case completely will be completely burned in a shorter barrel.
Maybe try VV N565? Supposed to have a little more velocity with the double base burn rate, esp in a short barrel?
Hate to do it, but I may have to actually buy a box of factory ammo from Hornady in 7prc to compare.
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