Twist rate has no bearing on pressures and velocities. Bore and groove size and I'll throw in the exact chamber spec are going to have the impact on pressures and velocities. All the data I've ever seen on p&v test barrels the twist rate means diddly squat. Doesn't matter if it's a 308win., 6.5CM etc... a 12 twist barrel produces the same pressures as a 8 twist barrel. Given the bore and groove sizes are with in proper tolerance and same reamer was used.
Every cartridge has a low and high accuracy node. Usually the low node has a wider tune window. Again in my opinion the twist will have nothing to do with a wider or narrower tune window.
A lot of shooters seem to always forget about the bullets and the powder. I'll put it one way right now and this is how the bullet/ammo maker and powder makers say it.... "the bullet, powder and barrel....these three things have to work together." If one is off that doesn't mean the barrel is bad or the powder is bad or the bullet is bad.
What powder you using?
What powder charge?
What bullets exactly?
What reamer spec cut your chamber/throat to?
What velocity are you getting?
How many rounds on the barrels? If less than say 60ish.... wait as the barrels usually speed up a little. Not all the time but it's normal because your laying down the carbon and that's what causes the speed up. Also how your cleaning it and how often in between the number of rounds fired makes a difference as well.
Also shooters over look the bullet big time. You/we assume the bullet should just shoot. I know one bullet maker holds the tolerance of they're match bullets for example to size +.0002". They're size could be .2642" + .0002" for example. But another bullet maker could hold size and lets say it's zero which would mean .2640" and they're tolerance is +.0007" or +.0009"! Now factor in the actual barrels bore and groove size. See where I'm going with that?
I always say this.... go for the accuracy first. Let the velocity fall where it is. If your getting (I'm just picking numbers here), Sub half inch groups and your velocity is at 2700fps.... but you bump the powder charge and your trying to get to 2800fps but the accuracy goes to 3/4moa... run it at 2700fps. I'll take the accuracy first.
Need more info brother!
Later, Frank
Bartlein Barrels
Thank you for taking the time writing this for me sir.
On my hunting rifle proof 26 inch sendero ligh barrel, my max velocity node without ejector mark was :
39.9grs of h4350, 147 ELD, cci 450 and lapua brass@ 2627fps
There is 530 rounds on this barrel.
The gunsmith used his own reamer.
I clean every 50-100 rounds, always get rid of the carbon ring and copper.
The new bartlein barrels are chambered with my newly purchased JGS 6.5cm Saami reamer.
I duplicated the load for the new bartlein barrel on my target rifle to just fire form the virgin brass, I wasn’t able to chrono the shots due to the issue I had with the Labradar, but didn’t have any pressure signs on those 50 pieces of brass I shot and I had some sub 0.5 inch 3 shots groups with Bartlein HV 1:7.5
I think that proof barrel is super slow comparing to even hornady manual and other folks with similar setup.
I will report back about the final load after I come back from vacation.
Thank you again Frank, I got all the answers I needed and now it all makes sense to me.
Max
