What twist should I get

[44man]

Well, found out why the new Savage was not shooting, it was Joe with a different pressure on the gun. I shot it and shot some good groups, cast running around 1" at 100.
When we tried my home made lead sled it was much worse, the thing bounces and throws the gun. Those things need bolted down.
The 165 Hornady shot very good with 4350 but Joe hates the recoil, he is skinny.

[Larry Gibson]

I found this website which provides what is in my opinion a more useful representation of twist and stability that the usual calculator http://www.geoffrey-kolbe.com/barrel_twist.htm


Taking the charts as gospel with a velocity of 1300fps or greater a 1:16 would even work, I shouldn't be surprised, doesn't the 32-40 shot 200 grain bullets from a 1:16 twist?

Yes the 16" twist in a .30 caliber does work extremely well stabilizing bullets under 1". That is what my 30x60 XCB rifle has; a 31" long Palma contour Broughton 3 groove barrel with a 16" twist. However, you the OP stated you have a 10 and 14" twist available and asked which of those would be best with the cast bullets he mentions. The 14" twist is your best choice, and not a bad overall 30 caliber twist for cast bullets at that.

Larry Gibson

[andym79]

I wasn't saying I had to get a1:16 just surprised it would stabilize all of those bullets.

[Larry Gibson]

Andy

My bad, that came out wrong. Was just trying to give you the 16" twist barrel info I use. I must not have drank enough coffee.......my apologies.

Larry Gibson

[andym79]

That's okay. I was just trying to clarify.

I am coming to think more and more that twist rate especially with cast is very important and that too fast might not be a problem with jackets but it is with cast.

The rpm threshold is real the Swede taught me that and since I am only becoming more sure. That's a big reason I think the the 32-40 and 38-55 shot well with cast. I know my 38-55 will out shot my 30-30. In part because the big bullets are easier to make good ones but the twist of 1:16 vs 1:10 sure makes a difference.

[centershot]

"In part because the big bullets are easier to make good ones but the twist of 1:16 vs 1:10 sure makes a difference."

Amen to that, brother!

[Larry Gibson]

The larger the diameter of the bullet the more mass it has from the center of it's axis of rotation. Thus it has greater rotational velocity at a given rate of spin (RPM) than does a smaller diameter bullet at the same rate of spin (RPM). Only a certain amount of rotational velocity is required for stabilization. To have an equal factor of stabilization (Sg) the larger diameter requires less RPM (lower rate of spin) than does the smaller diameter bullet.

Yes it can be confusing......

Larry Gibson

[dondiego]

I have the same question regarding the 5.56. I have the option of getting a 1:9 twist or a 1:14 upper kit. I was planning on shooting cast at 55 grains and was leaning towards the 1:14 twist.

[C. Latch]

Just FWIW, playing with the stability calculator, a 14" twist should stabilize some 150-grain BT or 165-grain FB .308" projectiles...even a 180-grain round nose, at .308 velocities......perhaps not perfect stabilization and fully realized ballistic coefficient, but certainly stable enough to get decent accuracy. Jacketed bullets tend to be pointer and less dense (copper jackets, less dense than lead) than similar weight cast projectiles.....point being, the 1-14" should easily shoot not only your desired cast projectiles, but also light to medium weight jacketed projectiles.