Rate of twist question???

[Tyke8319]

What is your opinion as to what SINGLE rate of twist best stabilizes both a 405 gr and a 500 gr cast bullet in a .45-70 black powder cartridge??

[100str8]

1 in 18

[jimmykan]

According to Berger Bullets' twist rate calculator, 1 in 20 twist in a 45-70 is just enough to stabilize a 500 grain solid copper bullet (1.539" OAL, 0.200 G1BC) at 1200 fps muzzle velocity.

So 1 in 18 twist would be more than enough.

https://bergerbullets.com/twist-rate-calculator/

[ar15barrels]

According to Berger Bullets' twist rate calculator, 1 in 20 twist in a 45-70 is just enough to stabilize a 500 grain solid copper bullet (1.539" OAL, 0.200 G1BC) at 1200 fps muzzle velocity.

So 1 in 18 twist would be more than enough.

https://bergerbullets.com/twist-rate-calculator/

Copper bullets of the same shape are longer than cast bullets of the same shape so 20" is enough.
Now velocity starts to become important at these lower velocities so without him giving us the velocity and his weather conditions, there's no way to know what the minimum twist really is.
Therefore, I vote 1:20" twist.

[Tyke8319]

Copper bullets of the same shape are longer than cast bullets of the same shape so 20" is enough.
Now velocity starts to become important at these lower velocities so without him giving us the velocity and his weather conditions, there's no way to know what the minimum twist really is.
Therefore, I vote 1:20" twist.

Velocity from a .45-70 with 68.5 gr black powder is around 1300-1400 FPS with a 500 gr cast bullet. A 405 cast with 55 gr is about the same velocity.

I will not be shooting COPPER at all.

I was guessing a 1-18" is about right???

[kcstott]

Velocity from a .45-70 with 68.5 gr black powder is around 1300-1400 FPS with a 500 gr cast bullet. A 405 cast with 55 gr is about the same velocity.

I will not be shooting COPPER at all.

I was guessing a 1-18" is about right???

There's no way on god's green earth you're going to get 1300-1400 FPS with a 500 grain cast bullet. and 68.5 grains of black.Those velocities and powder charges are for a 336 grain bullet. In reality you're looking at 1100-1200 fps with a 500 grain bullet. I can say that with from experience as I own a Shiloh in 45-110 and with 104 grains or 1.5F OE a 545 grain bullet it can barley break 1300 fps.I also pulled numbers from Mike Venturino's book on buffalo rifles. SPG manual confirms this although Mike Venturino co autorthored that book too. The C sharps manual cites 1102-1118 FPS with 70 G of Fg depending on a 30" or 34" barrel. And even with 65 gr of FFg powder they only cite 1200-1218 FPS with a 500 grain cast lyman bullet. You might be able to squeak 50 more FPS if you used swiss powder but thats it. The 45-70 can not hit those number.
As to the best twist rate. Shiloh uses 1:18 for all 45 caliber rifles. They will make you a 1:16 if you ask. At the Ben Avery BPCR nationals you will find more Shiloh rifles than any other maker. Most 45's are going to be 45-90 or 45-110 almost all are 1:16 twist and 30 to 34" long.

[Tyke8319]

I should have been clearer. The 1300 fps would be appropriate for the 405 and about 1000 +/- for the 500.
I' going with the 18-1 twist.

[kcstott]

I should have been clearer. The 1300 fps would be appropriate for the 405 and about 1000 +/- for the 500.
I' going with the 18-1 twist.

No you were pretty clear. You just over estimated your numbers.
1300 FPS is still going to be very tough to hit in a 45-70 with a 405 gr bullet. All data points to 1200 at best unless you run swiss. 1000 fps with a 500 gr in a 45-70 is reality. 1100 with a 400 is also reality.