25-06 velocity loss

[dig]

Ok so I just put a new Benchmark barrel on my 25-06. It's 27 inches and it replaced a Shilen same length and contour. Twist was changed from 1/10 to 1/9 as we keep getting heavier projtiles. My velocity with the same lot of reloads dropped almost 100 ft from 3174 to 3083 10 round average. It's accurate and repeatable with the sam load, SD is 22 so I can't complain to much but a little bummer about the drop. Any thoughts, guess I will start playing with my charge weight, just have a lot of stuff loaded already.

Load is Berger 115 with 53 grains 4831sc

 

[red dawg]

I believe when you put 50 to 75 rounds down the tube the velocity will be back, I'm guessing you haven't shot it much ?

 

[Barrelnut]

Check this out:Does Barrel Twist Rate Affect Muzzle Velocity? (Litz Test) « Daily Bulletin

 

[Bart B]

Slug both barrels and measure the groove diameter to the nearest .0001" and you may see a difference. The one with smaller groove diameters will typically shoot the same load faster as long as the bore diameter and chamber dimensions on both are the same.

The difference in rifling twist needs both barreled actions to be fixed in a hard mount so the difference us humans hold the rifle against our bodies across several shots won't cause a muzzle velocity spread. People chronoing loads in a free recoiling rifle see lower muzzle velocities as well as lower muzzle velocity spreads than when holding it against their shoulder. In a fixed mount, the barreled action shoots loads the fastest and with the smallest velocity spread.

There's been instances of two different lots of powder showing almost 100 fps difference in muzzle velocity. And differences in how the loads are assembled (case neck grip on bullet) can also cause big velocity spreads.

I don't see anything in that link stating all 6 barrels having the same exact bore and groove dimensions.

 

[dig]

All good replies, thanks everyone. Like the Litz article! I have 25 rounds down the tube so will continue to break it in, great point on the bore diameter, another variable. Like I said, its grouping well at .60 at 100 with zero load work up, so I really cant or should not complain. Fairly light weight rig at 8.5 +/- with scope. I will adjust my Balistics Calculator and get out to 600 yards this weekend. Lots of variables to consider here, more curiosity on my part than anything, Load is below published max so I have some room but I will take accuracy over velocity any day! clean up on this barrel has been very easy! Started cleaning after 3 shots first 9, then 5 so getting close to break in.