[mudman35962]

big question here. [may not be the first]
thinking of a rifle build with a rolling block action. when looking into a supplier for a octagon barrel first stop was green mountain. 38-55 information gives a choice of 1-12, and 1-14. Lymann 50th data used a 1-20. this seams like a big difference. the data uses 249gr, and 355gr cast lead. i will be using cast at mid range [1600fps +/-]
would either of these barrels work for me? i can not get my head around the twist rate thing. opinions will vary, facts not so much. i would like a source that i can understand [simple] so i can get this correct the first time. are other factors that are important involved? barrel length maybe?

 

[Grizzley1]

The two biggest factors are velocity and bullet length and diameter.

 

[SafetyFirst]

Here is a link to a post in another forum from a member who really knows guns: bullets and barrel twist
Especially read post #10 by Iowegan.

 

[Grizzley1]

Here is a link to an online calculator, type in the information in the boxes and it does the math for you.Barrel Twist Calculator

 

[sharps4590]

Greenhill formula. As far as I know it is the formula on which all others are based. It's what I use when I get a rifle that I have to calculate everything.

 

[mudman35962]

big question here. [may not be the first]
thinking of a rifle build with a rolling block action. when looking into a supplier for a octagon barrel first stop was green mountain. 38-55 information gives a choice of 1-12, and 1-14. Lymann 50th data used a 1-20. this seams like a big difference. the data uses 249gr, and 355gr cast lead. i will be using cast at mid range [1600fps +/-]
would either of these barrels work for me? i can not get my head around the twist rate thing. opinions will vary, facts not so much. i would like a source that i can understand [simple] so i can get this correct the first time. are other factors that are important involved? barrel length maybe?

OK went twist twist rate calculator and put in information as i know it. i am told that 1-20 is correct for either 249gr and 355gr bullets.just as Lymann says. green mountain barrels are offered in 1-12 and 1-14 twist. will they work? should i go elsewear? i will call them to get their input on this. i am just asking for member thoughts, you have been helpful so far
don't stop now. "inquiring minds want to know"

rick

 

[Grizzley1]

If I remember right the last barrel I made for the .38-55 was a 1:20 twist, but I have been asked to make them in 1:18, 1:16 and 1:14. The older black powder/cast lead cartridge versions used slower twists than modern smokeless/jacketed bullet rifles. In general, longer bullets like a faster twist rate, shorter bullets can use a slower twist rate. You might give Green Mountain a call and find out what bullet they recommend in their barrels. You might also find out if these barrels are .368/.375 bore and groove or .370/.379. The smaller of the two being for the .375 Winchester, a modernized smokeless version of the .38 - 55. 12 and 14 twists seem to me to be better suited to the modern .375 Winchester round.
Now that I've got you completely confused I have had requests for .38-55 barrels using the .375 bore dimensions and twist rates, they said they were planning on using jacketed .375 bullets because they were more commonly found and in wider selections than .38-55 bullets.