Gentlemen,
I am expecting the delivery of my 6mmBRNorma rifle from Kelbly's within the next couple of weeks. It will have two barrels, both with,no-turn) .272 necks. A common recommendation is to use a loaded round that is .002 smaller than your chamber neck.
Now, I have started to prepare the Lapua brass. Minimal trimming and chamfering, FL resizing as well as primer pocket uniforming.
I then started to look at the neck wall thickness,with a RCBS casemaster gauging tool) I found the Lapua brass to be better than most, but not perfect. I sorted the brass in 3 piles, one with "next to nothing" variance, the second with up to 0.0005" and the third above that.,It seems that the variance does not exceed 0.001.) The precision of the RCBS tool may not be the best, but I don't have a ball mike, only a normal one for measuring loaded rounds.
Since I have a KM neck turner, I am now confronted with the question "to turn or not to turn". And if so, how much? Clean up the high spots or make sure that the variance is eliminated. By eliminating the variance the clearance will increase with, let's say a total of 0.0005", if I use the better pile of brass. Now this pile was, not surprisingly, the smallest with about 20% of the cases.
Within the hall of fame BR shooters, there seems to be no real consensus which clearance is "optimal". And any reason for their choice of clearance is not given.
Now, did anyone do some testing on the issue, such as shoot with cases with about .001 variance - then clean up for reduced variance - and finally make the last cut to eliminate variance.
Further, did anyone test different clearance on, the very same, cases. I.e. cases without variance just different clearance. And using the same diameter bullets.,Some oversize bullets have pressure rings in the range of .244, so they reduce the clearance compared to the std .243 bullets)
Looking forward to interesting observations.
Richard
I am expecting the delivery of my 6mmBRNorma rifle from Kelbly's within the next couple of weeks. It will have two barrels, both with,no-turn) .272 necks. A common recommendation is to use a loaded round that is .002 smaller than your chamber neck.
Now, I have started to prepare the Lapua brass. Minimal trimming and chamfering, FL resizing as well as primer pocket uniforming.
I then started to look at the neck wall thickness,with a RCBS casemaster gauging tool) I found the Lapua brass to be better than most, but not perfect. I sorted the brass in 3 piles, one with "next to nothing" variance, the second with up to 0.0005" and the third above that.,It seems that the variance does not exceed 0.001.) The precision of the RCBS tool may not be the best, but I don't have a ball mike, only a normal one for measuring loaded rounds.
Since I have a KM neck turner, I am now confronted with the question "to turn or not to turn". And if so, how much? Clean up the high spots or make sure that the variance is eliminated. By eliminating the variance the clearance will increase with, let's say a total of 0.0005", if I use the better pile of brass. Now this pile was, not surprisingly, the smallest with about 20% of the cases.
Within the hall of fame BR shooters, there seems to be no real consensus which clearance is "optimal". And any reason for their choice of clearance is not given.
Now, did anyone do some testing on the issue, such as shoot with cases with about .001 variance - then clean up for reduced variance - and finally make the last cut to eliminate variance.
Further, did anyone test different clearance on, the very same, cases. I.e. cases without variance just different clearance. And using the same diameter bullets.,Some oversize bullets have pressure rings in the range of .244, so they reduce the clearance compared to the std .243 bullets)
Looking forward to interesting observations.
Richard
