Velocity changes with twist rate of barrel ?

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Josh Cox
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Velocity changes with twist rate of barrel ?

#1 Postby Josh Cox » Tue Dec 17, 2019 10:29 am

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

Rich4
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Location: Chinchilla

Re: Velocity changes with twist rate of barrel ?

#2 Postby Rich4 » Tue Dec 17, 2019 11:00 am

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 :twisted: , regards Rich

Peterla
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Location: Barossa Sth Australia

Re: Velocity changes with twist rate of barrel ?

#3 Postby Peterla » Tue Dec 17, 2019 4:26 pm

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.

Wal86
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Re: Velocity changes with twist rate of barrel ?

#4 Postby Wal86 » Tue Dec 17, 2019 5:35 pm

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

6.5x55ai
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Location: Waikato NZ (Ex Tyabb)

Re: Velocity changes with twist rate of barrel ?

#5 Postby 6.5x55ai » Wed Dec 18, 2019 5:28 am

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.

Pommy Chris
Posts: 441
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Re: Velocity changes with twist rate of barrel ?

#6 Postby Pommy Chris » Wed Dec 18, 2019 2:31 pm

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

ShaneG
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Joined: Fri Jun 15, 2012 2:25 pm
Location: Cairns

Re: Velocity changes with twist rate of barrel ?

#7 Postby ShaneG » Wed Dec 18, 2019 7:46 pm

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?

Frank Green
Posts: 343
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Re: Velocity changes with twist rate of barrel ?

#8 Postby Frank Green » Thu Dec 19, 2019 12:56 am

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

Frank Green
Posts: 343
Joined: Wed May 28, 2014 11:48 pm

Re: Velocity changes with twist rate of barrel ?

#9 Postby Frank Green » Thu Dec 19, 2019 12:59 am

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


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