Case pressure vs barrel twist

[Dcrafton]

With everything being equal.
Same bullet, same load data, same velocity..
If I only change the twist (let’s say from a 1-9 to a 1-8) how much more pressure may I increase?? This would be in a 280ai


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[lcxctf2000]

Interesting question. What makes you think a twist change would change pressure? My gut says it would have little to no effect.

 

[jorgensen.travis]

Seems like it would increase pressure because of the extra friction. With the same load, velocity should go up as well.

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[Dcrafton]

I read that some years ago, but just don’t remember much of the article. Was hoping that someone would have more information than I. It kinda makes sense that to force the bullet to spin faster in the same distance pressure would rise.


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[Dcrafton]

Would it be safe to say, if I lower load to match the same safe operating pressure I may be able to keep the same velocity??


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[lcxctf2000]

Well, given that I assume you'll be using a new barrel to get this different twist rate you should work up an entirely new load for it.

Chamber and throat differences would account for more pressure changes between the two barrels than twist rate by a long shot I would assume.

 

[lcxctf2000]

Seems like it would increase pressure because of the extra friction. With the same load, velocity should go up as well.

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I won't claim to be a physics whiz here but I think the force we are talking about changing is rotational inertia rather than friction.

I can absolutely see that the force required to accelerate the same mass bullet to rotate slightly faster could be higher and result in higher pressure.

I think there are lots bigger factors at play though assuming we are using a different barrel to get a faster twist

 

[Dcrafton]

So if I use a faster twist, to get the same velocity I may be running at a higher pressure.
Yes developing a load specific for the rifle would be done.
Just trying to figure out things about pressure, velocity and barrel twist.


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[lcxctf2000]

So if I use a faster twist, to get the same velocity I may be running at a higher pressure.
Yes developing a load specific for the rifle would be done.
Just trying to figure out things about pressure, velocity and barrel twist.


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I have to ask - what setup are you using where you would want to change only twist rate?

Usually twist rate is changed so you can get a lighter or heavier bullet to stabilize and it sounds like you want to keep the same bullet.

 

[ckleeves]

My .02, you really won’t know until you put some rounds downrange through the new barrel. To many variables besides just twist rate to take into account. Every barrel is somewhat of an individual, especially if your changing manufactures. If you had two barrels from the same manufacture each with a different twist rate and chambered them with the same reamer and screwed then on the same action you “might” be able to come up with an answer. Litz did this and came up with a whopping 1.33 FPS per inch of twist rate.

I really wouldn’t sweat it. Buy whatever twist you want and work up till you hit pressure. It might be faster or slower then the old barrel. Really only one way to find out. 1/4” of barrel length could make more difference then a 1” change in twist rate.


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[Dcrafton]

Here the back story,
I sold a 280ai with a 1-9 do I can find a custom build.
My custom build is,
ARC nucleus action,
Proof research carbon (24”) 1-8
McMillan A3 edge tech stock (cerakote stock only)
Jewel trigger

That’s why I’m asking about the difference



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[rayporter]

agree with the above-there may [may] be a different pressure in the new barrel but even if it was the exactly the same as the old barrel there could still be a difference in pressure. a different barrel has different dimensions and frequently a different node for accuracy no matter how hard you try to duplicate the old one. it will not likely be the twist that is the reason, and because of all the other changes in a new barrel [ new throat for one] you wont know for sure if it is the twist.

I have 14 barrels for one rifle and many take a different load, even though they were chambered with the same reamer.

 

[lcxctf2000]

Here the back story,
I sold a 280ai with a 1-9 do I can find a custom build.
My custom build is,
ARC nucleus action,
Proof research carbon (24”) 1-8
McMillan A3 edge tech stock (cerakote stock only)
Jewel trigger

That’s why I’m asking about the difference

Sounds like a nice build and absolutely understand the question being asked in that context. Curious to see what your results with working up a load are when you get it done. Good luck and have fun!

 

[Ndbowhunter]

I think ur over thinking this a bit.

Get a 1/8 twist for ur 280 and be done. No problem with 110 tnt bullets all the way up to 180 eld-m

Don’t get caught in the minutia.

 

[Dcrafton]

I agree I am over thinking this, but it’s good for me as I like to make sure of what I am doing when it comes to reloading.
Thanks for all the good information


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[gbflyer]

This could shed some light on it. This fellow knows his stuff:

http://bulletin.accurateshooter.com/2015/02/does-barrel-twist-rate-affect-muzzle-velocity-litz-test/

 

[rayporter]

frank green says:
February 9, 2015 at 9:16 am
For the most part the twist rate doesn’t have an effect on pressures. We make a ton of ammunition pressure test and accuracy test barrels as well. All the feedback I’ve gotten on pressure test barrels is that the twist again doesn’t really effect pressure.
Changing the bore/groove size (total surface area of the bore) and or changing the chamber reamer/throat specs. is going to have a bigger impact on pressures and velocities.
I have to praise Bryan for taking the time to do the test and taking as many variables out of the equation as possible to get good and consistent data. You won’t get a commercial gun or ammo maker to make this information public etc…
Later,Frank
Bartlein Barrels

 

[gbflyer]

frank green says:
February 9, 2015 at 9:16 am
For the most part the twist rate doesn’t have an effect on pressures. We make a ton of ammunition pressure test and accuracy test barrels as well. All the feedback I’ve gotten on pressure test barrels is that the twist again doesn’t really effect pressure.
Changing the bore/groove size (total surface area of the bore) and or changing the chamber reamer/throat specs. is going to have a bigger impact on pressures and velocities.
I have to praise Bryan for taking the time to do the test and taking as many variables out of the equation as possible to get good and consistent data. You won’t get a commercial gun or ammo maker to make this information public etc…
Later,Frank
Bartlein Barrels

Must be an echo around here