OzFclass

Has anyone tested the change on velocity for twist rate of the barrel, ie same load in a 10 twist versus 12 ?

Not me, but it’s been discussed ad nauseum all over the net, Frank Green would be the man here, I believe the common result was any change gets lost in the noise from barrel to barrel, unless it’s a drastic change say 14 to 7, but generally slower will be less pressure (cockie logic) but the projectiles for different twists are so different to render a comparison theoretical only, that being said I’m currently testing if an ultra slow will allow warp speed , regards Rich

Then you get Fast and slow barrels that will confuse the results. I have 2 barrels of the same manufacturer and 1 is 50FPS faster than the other for the same load and same projectiles!!
That might mix the results so you would need to get an average of quite a few barrels to get the real feeling of the difference.

Twist rates only have a minor effect on velocity, bore dimensions have a much greater effect on pressure/velocity...

Twist rate is also not one of the inputs for Quickload so they don't see differing twists affecting pressure/velocity. (Not saying QL is the be all end all.)

There was a thread sometime back on this topic as well and I think Frank did comment on that occassion as well IIRC to say no effect.

I have too many barrels so not getting one now but I have been curious of a gain twist barrel for a while, this would give low pressures lower barrel wear (lower pressures) and correct twist when leaving the barrel. Problem is gain twist is hard to make.
Chris

Bartlein have been offering it as custom for a long time
CNC accurate
The little I have spoken with people using it is only small increments are best?

Pommy Chris wrote:I have too many barrels so not getting one now but I have been curious of a gain twist barrel for a while, this would give low pressures lower barrel wear (lower pressures) and correct twist when leaving the barrel. Problem is gain twist is hard to make.
Chris

Not hard to make per say. We make them all the time. For a button barrel maker it's going to be more difficult to make. Why....you can try and spin the button a little faster as you pull/push it thru the bore but you force it too much and the button usually shatters.

Later, Frank
Bartlein Barrels

Wal86 wrote:Twist rates only have a minor effect on velocity, bore dimensions have a much greater effect on pressure/velocity...

What he said!!!!!!

Also chamber reamer spec....you can physically have two identical bore/groove size barrels. Cut a chamber that will give you a tighter/shorter throat spec....and it can effect the pressures and velocities as well.

That's why I tell guys unless you know bore and groove size to the 4th decimal place and what reamer was used to cut the chamber you are not comparing apples and apples.

Now throw in another variable.....ammo, bullets etc...get a fat bullet that fits tighter in the bore and this can cause variations as well.

Later, Frank