Barrel twist 1:7.5 or 1:8

[Montanaatheart]

Howdy all. Just looking for some insight on how much one can expect a difference in speeds (if any) if all things being equal ((they never are -barrel length and load - same reamer created both))? I realize barrels vary so am just more of a general expectation, if one has a 4r 1:8 compared to a 5r 1:7.5.

 

[Varmint Hunter]

Howdy all. Just looking for some insight on how much one can expect a difference in speeds (if any) if all things being equal ((they never are -barrel length and load - same reamer created both))? I realize barrels vary so am just more of a general expectation, if one has a 4r 1:8 compared to a 5r 1:7.5.

From a practical standpoint - no difference in speed. If you went from a 14" twist to an 8" twist than, maybe, there would be a measurable difference, but I doubt that it would be meaningful.

 

[FEENIX]

Howdy all. Just looking for some insight on how much one can expect a difference in speeds (if any) if all things being equal ((they never are -barrel length and load - same reamer created both))? I realize barrels vary so am just more of a general expectation, if one has a 4r 1:8 compared to a 5r 1:7.5.

I agree with @Varmint Hunter. On my last three builds, I went with "or faster" for the twist recommendation of the bullets I am using: .257 WBY and .264 WM are 1:7" and .338 Thor is 1:8", and so far, so good.

 

[MagnumManiac]

It has been measured many times twist and number of grooves has very little affect on velocity, but WIDTH of rifling does, albeit a very small amount.
If anybody remembers 'micro-groove' barrels, these were faster than Ballard type rifling, but fouled in less than a 1/4 number of shots.
I had one, what a DISASTER that was.

Cheers.

 

[FEENIX]

It has been measured many times twist and number of grooves has very little affect on velocity, but WIDTH of rifling does, albeit a very small amount.
If anybody remembers 'micro-groove' barrels, these were faster than Ballard type rifling, but fouled in less than a 1/4 number of shots.
I had one, what a DISASTER that was.

Cheers.

Bryan Litz covered it in more detail in his book, but I do not have it. Here's an excerpt.

https://bulletin.accurateshooter.co...-twist-rate-affect-muzzle-velocity-litz-test/

 

[Darkker]

Wow.... That was a steaming pile of an article beginning, even for Brian....
Accurate pressure measurement equipment in point of fact, has been available to the general public for longer than stupid QL has. And it cost less than QL, for the bulk of it's existence...

As far as twist rate, no it has absolutely no effect on pressure; and therefore velocity.
If you want real ballistics knowledge from someone who actually understands the subject, go buy Jeff Siewert's book.