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If the barrel wasn't perfectly cleaned before being sent it will create pockets in the nitriding, then when barrel comes back from nitriding Id wear out two bronze brushes cleaning to remove the crud, often it looks like rust at first.
Bartlein uses a 5R cut rifle a fast twist 1-7.5 It is easier on the jackets than a 1-7.5 button 6 grove . Example my Bartlein 1-7.5 will be easier on the 147 gr jackets than my Proof if it was a 1-7.5 so my Proof is a 1-8 twist. The only thing that can cause that kind of inaccuracy in my opinion is the bullet is coming apart.
Fennix I didn't mean too quote you , I posted in the wrong spot , my apologies.
When I built my last 6.5 Prc Straight Jacket Aromory said that the 1-7.5 twist Proof barrels were spinning the jackets off of the 147 gr eldm bullets . I went with the 1-8 in that type of rifling 6 grove button . I also think that Hornady had a batch of bullets in the 147 gr that was more prone too that problem .
That is good to know; I could be wrong but loading the 156 will do any better. You might consider @bigngreen point and address it to whoever did the nitriding.
I suppose that is possible. My .257 Wby is a 5R 1:7" and I used 2 boxes of factory ammo with 100g SP by Weatherby to break in the barrel. The ammo was loaded for 1:10" but did not have any issues being propelled out of 1:7" at 200 yards.
That is my point the 5r will allow a faster twist with thin jackets the 6 groove button is harder on the jacket
Sorry, I meant to quote your #67 post about over-stabilizing instead of #73; thus, the reference 1:7" vs. 1:10" for the 100g SP.
Can the action be sent to Brux to check out the Barrel, and see if there is an issue with it?
Probably not your problem but several years ago a gunsmith told me that someone brought him a 22-250 that was keyholing and even missing the 100 yd target. The gun was pristine condition on the outside. The gunsmith cleaned the bore and actual pieces of rust came out. The barrel was then so pitted that it was worthless. The problem had been the rust was damaging the bullet to the point of it tumbling and occasionally flying apart due to the deep gouging in the jacket. Loose screws or bad scope would not make a bullet fly apart or tumble in flight. I have shot a rifle that the action screws were finger tight and the scope was loose on the bases and it would still shoot under a foot. There must be something so wrong with your set up that it should be easy to track down.
