What should I expect as I start loading for my polygonal 6mmBR, 10 twist, 26" bbl? Seems to be a lot of rumors through the years about poly's being 5-7% faster than conventional rifled bbls, but I have never tried one until now. I guess I will find out, but if it is true they would pr duce velocies in the std 6mmBR that equal those from an improved version, if that is true are they not as accurate? Why aren't they seen? Mine is for varmits so I don't need BR accuracy to play. Just wondering,,,, JimDee
Polygonal bbls velocity?
- Thread starter oldjad01
- Start date
First tests were encouraging, but of course not conclusive. Worked up three different loads for the 87VMax:
32gr Varget @ 3150fps
29gr AA2520 @ 3015fps
30gr AA2520 @ 2978fps
CCI BR4 Primers, Lapua cases, o/a length 2.165, 62-70F, 2000ft altitude, 2-5mph shifting breeze. No heavy bolt lift or flattened primers and the max expansion at the pressure ring .001",
You will note that the varget and 2520 loads run higher than the Hodgdon manual. I am thinking that the poly rifling might give lower pressures than ballard type, kind of like moly bullets, and require more powder to reach good working pressures,?). Of course the moly question is a much more widely debated topic than the poly bbl one.
I didn't load anything heavier using 2520, It had a constant .001 expansion from the starting load right to the last. I would like some one to expain that if they can. Accuracy was constant: mediocre <= .5" 3 shot 100yd groups.,The '<' is here by the barest of measurements.) But then again I was shooting so badly that a 50# BR gun probably would not have helped. JimDee
32gr Varget @ 3150fps
29gr AA2520 @ 3015fps
30gr AA2520 @ 2978fps
CCI BR4 Primers, Lapua cases, o/a length 2.165, 62-70F, 2000ft altitude, 2-5mph shifting breeze. No heavy bolt lift or flattened primers and the max expansion at the pressure ring .001",
You will note that the varget and 2520 loads run higher than the Hodgdon manual. I am thinking that the poly rifling might give lower pressures than ballard type, kind of like moly bullets, and require more powder to reach good working pressures,?). Of course the moly question is a much more widely debated topic than the poly bbl one.
I didn't load anything heavier using 2520, It had a constant .001 expansion from the starting load right to the last. I would like some one to expain that if they can. Accuracy was constant: mediocre <= .5" 3 shot 100yd groups.,The '<' is here by the barest of measurements.) But then again I was shooting so badly that a 50# BR gun probably would not have helped. JimDeeI use moly and shoot a poly barrel setup by GAP. It is a .308 Schneider 5P 24",M700 action in an A5 stock and I do most of my shooting at HardRock in AL. I have found that I have to drop most "Suggested"loads by a full grain. This is especially so using LC LR brass and even Lapua brass. It would appear that the poly barrel has less gas leak and gets maximum use of whatever load. Am currently running 178 Amax in LC LR and using Benchmark powder at .7 grs UNDER Hodgdon Load for 175. Accuracy is <1MOA out to 600ydsand that is what I am looking for. I would say the rifle is shooting much less than MOA but that is a given for a GAP. Gotta add in the "nut" on the trigger !!
Yep, my 1st post. Goto Snipers Hide and look for the same name. Have lurked here for some time but I Will be back !
Yep, my 1st post. Goto Snipers Hide and look for the same name. Have lurked here for some time but I Will be back !
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