Rate of twist

[Anduril]

Does anyone have an opinion (oh boy) on a good twist rate for a new black powder barrel on a 45/70 rolling block? I would like to shoot 400 grain cast and bp.
thanks.

[John Traveler]

The US Army research establishment at Springfield Armory standardized on the 1-in-22" twist for the .45-70 rifle in 1872.  For simplicity in manufacturing, they also used this twist rate for the 22" carbines, both firing the then-standard 405 grain bullets at about 1300 and 1200 fps, respectively.

BPCR shootors favor longer-than standard .45 bullets (500-550g) and like the faster twist rates such as 1-20, 1-18, 1-16, etc.

For general purposes, and all around bullet weights the 1-22 is still good..

If you ask the people at Badger and Green Mountain, etc what sells best in their BPCR .45 barrels they will probably tell you 1-20".

[Anduril]

Thanks John.
I have a line on a Douglas barrel with a 18" twist.  Any downsides?  Is it possible to "overstabilize" a bullet with too much spin?

[John Traveler]

Your 1-18" Douglas will do fine for the entire range of .45-70 bullets you intend to load.

It's not perfect for say, 300 grainers at low velocdities, but will be more than satisfactory with full loads for the 400, 500, etc grain bullets for the long range events.

[cooper]

Technically, I don't think it is possible to "overstabilize" a bullet.  That is, the bullet is either stable, or unstable.  There is no such thing as over-stable.

However, for absolute top accuracy, there seems to be a particular twist rate, dependent on the bullet length, which will give you the best accuracy.  This is something that interests competitive benchrest shooters, but the difference in accuracy is probably too small for anyone else.  I think we're talking in terms of .05 to .1  minutes-of angle or thereabouts.

In my opinion, DEFINITELY go for the quicker twist.  It will enable you to use longer bullets if you wish; it will still work fine for shorter bullets, and there is almost no downside to it.   About the only downside may be that the "torque" you feel during recoil (due to the quicker twist) MAY be a little more noticeable, and if you shoot blackpowder, fouling MAY accumulate a bit faster in the quicker twist.  

I'm not sure whether you will even be able to notice these effects - but even if you do, I think they are minor, and in my book they are worthwhile tradeoffs.

[PA-Joe]

Actually, for some of the very small calibers with light plating too fast a twist will over spin and break them apart. I don't think you will have to worry about that with a 45-70.

[Anduril]

Thanks.  It sounds like a done deal.