Ironworker said:
Loaded these bullet 015 and 007 and touching lands…
Why would you believe that range would give you best results? Let me guess. Someone said it would. In the past "someone" has said 0.020" off the lands is best. Someone else has said 0.025". Someone else has said 0.030". And guess what. They were all correct—for their chamber and bullet.
Writing in the 1995 Precision Shooting Reloading Guide, the late Dan Hackett described having a 40X in 220 Swift that refused to shoot as well has he would like with the bullets 0.020" off the lands. He knew that 0.020" was best because, well, somebody said it was and everyone knew it. But he could never get 5-shot groups better than 3/8, and most of them were bigger, averaging about 1/2", and no adjustment he made to the powder charge would fix it. So, one day he was assembling his best load and switched to a Nosler Ballistic Tip which was 0.015" shorter and he changed his seating die micrometer seater because it needed to be seated 0.015" further out to be 0.020" off the lands, which he knew was best for the above mentioned reasons. But he accidentally turned the micrometer the wrong way, seating them 0.015" deeper. Since they were already that much too short, he actually backed them up a total of 0.030" from the desired distance so they were now 0.050" off the lands. He loaded 20 like that before he notices. He debated pulling them and re-seating them, but decided just to shoot them in practice. Good thing. They gave him two groups 1/4" across and two bugholes in the 1's (less than 0.2" across).
Berger has discovered that some rifles shoot their secant ogive VLD's best seated anywhere from touching the lands to as much as 0.150" off the lands.
Ironworker said:
… with 40.7 grs of Superformance
Why did you think that particular powder charge was going to give you best accuracy? Unless it produces a barrel time that synchronizes the bullet exit with your particular gun barrel's natural phase of best exit time, it won't. Normal procedure is to adjust charges in increments of about 0.7% to as much as 1%. About 0.3 grain steps for that powder in your gun.
Dan Newberry describes it.
The main issue in all this is that both adjusting powder charge and seating depth affect barrel time. Powder affects it more, so you usually tune to best powder charge touching the lands, then start seating deeper as Berger describes (use 0.020" steps for shorter ogive bullets that aren't VLD's, like the Sierra) until it gets better. Retune the powder charge, as the best spot will have shifted a little, and then you can try finer adjustments to seating depth if you can see any difference. You are playing with two interacting variables, so the readjustment is inescapable.
Some powders just don't have a burn characteristic that ever likes a particular barrel or chamber. If that's the case, try Sierra's powder recommendation.
