Need help with correct twist

[rick983]

I'm building a 45 Long Colt rifle on a T/C Contender and plan on using a 17" barrel and a suppressor. I will be shooting 250 gr. and larger lead bullets at less than 1100 fps. What twist would you recommend? Thanks in advance.

[felix]

26 would be plenty fast. ... felix

[44man]

1 in 20 Felix! You need rifle velocities for the slow twist you recommend. I would not go less then 1 in 24 in any case.

[joeb33050]

If we use the approximation that a cb weighs 82% as much as a cylinder of the same length, then Greenhill tells us that
a 26" twist will stabilize a .457" bullet 1.205" long weighing 464 grains, or any shorter bullet.
a 20" twist will stabilize a .457" bullet 1.566" long weighing 603 grains,...
For 250 grain and LIGHTER bullets, a 48" twist works.
To fiddle with the numbers, see the book, the EXCEL workbooks, the Greenhill Workbook.
joe b.

[leftiye]

Remember tha 1100 feet per second speed limit! I'd even say 1 in 16 maybe. Which same (or thereabouts) is standard for .45 L.C. anyhoos. Rick, this .45 cal at 1100 fps. is the formula I've liked for a long sime for a silenced weapon. Though I wanted a little heavier jacketed bullet (plus expanding). Please let us know how things go.

[44man]

How many have found that the Greenhill formula works? Nobody that I know anyway!

[Tom Myers]

Try this Twist/Velocity/Caliber calculator

http://www.uslink.net/~tom1/twistrate.htm

Tom Myers

[felix]

Seems to be accurate..... 850 fps, 0.454, 310 grainer (WW) as LFN (LBT 70%), 3.5 constant, 0.780 length..... twist = 27. ... felix

[shooter93]

I'd be inclined to use 1 in 20...it worked well for us anyway. As a side note....it's better if your suppressor can be taken apart for cleaning if you're using cast bullets. They do get a fair amount of lube residue in them and can get lead particles too.. You can soak them but I've seen times when that didn't work so well....it never really cleaned them out. Shoot the heaviest bullet you can....I;m doing a 452 diameter now to shoot 520 grain bullets. I use mostly softer lead bullets now as opposed to J bullets for game taking. In the rifle calibers...ie..the 300 whisper we had dismal performance on game with J bullets.

[joeb33050]

How many have found that the Greenhill formula works? Nobody that I know anyway!

With the possible exception of very slow bullets at very long ranges, I have never seen Greenhill fail.
joe b.