45/70 rifle twist

[loutex]

I have a 45/70 with 32in barrel and a 1/20 twist. I'm new and my question. The greenhill?? formula shows a 520gr .458 1.330long cast bullet should require a 1/23 twist but all I read says use a 1/18 twist. How do I figure range of cast bullets for my 1/20 with a bore diameter of .457? Thanks for any help to this newbie.

[Castaway]

I think that the difference is so slight that you won't notice a difference.  Shoot it and see what it does.

[FAsmus]

Loutex;

L:  I have a 45/70 with 32in barrel and a 1/20 twist. I'm new and my question. The greenhill?? formula shows a 520gr .458 1.330long cast bullet should require a 1/23 twist but all I read says use a 1/18 twist. How do I figure range of cast bullets for my 1/20 with a bore diameter of .457? Thanks for any help to this newbie.

F:  The 1:20 will not really stabilize the long 520 grain bullets very well. At short ranges such as 200 - 350 yards the difference will not be very obvious but if you intend to shoot at longer distances such as 500 (+) meters things will be coming unglued due to the slow twist: Bullet prints will show yaw angles in excess of 2 degrees and the further you shoot, the worse it gets.

Stick to the lighter bullets such as SAECO 65645 or Lyman 457125 and things will be better.

For Greenhill subsitute your velocity (as chronographed) divided by 100, for the contansant "150" in the formula as given. This will adust the math to your acutal rifle and load for a real answer so far as bullet stability is concerned.

Good evening,
Forrest

[loutex]

Thanks for the reply from ya'll. I was afraid I was going to have to find me a mold with a bullet length of 1.50 and that was going to be throwing about a 600 gr slug or thereabouts. More than I wanted. Again thanks.

[ButlerFord45]

lutex,

You're going the wrong way.  Basicly a longer bullet will need a faster twist.  Shorter=slower.  If it helps in your selection, My 457125's (500gr) are 1.320"  and the 405 flat point's I have are 1.045".