Small caliber twist rate?

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bang

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My understanding a slow twist is 1:60 and slower. Most accurate with PRB. Tends to reach best accuracy with bit more charge than faster twist. 1:48 up to just under 1:60 good for PRB, conical, bullet, mini and maxi. Faster than 1:48 and PRB less reliable but can become so with bit less charge to a point. When you get as fast as 1:3x or 1:2x PRB pretty much out of the picture.
Problem with faster twist is the pressure can cause a PRB to skip over riflings. Being front packed there is not compressed to bore fit coupled with purer soft lead that can't withstand the pressure friction and the patch won't hold. A mini works better because the pressure expands the skirt into the riflings. Even then excess pressure can cause some skipping but the skirt expansion still provides better rifling engagement even though it's still purer soft lead. 60-70 gns typically recommended charge range.
The groove depth can have some effect too. With groove depth over .005 a thicker patch helps to achive best gas seal. Just as long as the starting pressure is not a hammer in fit or loose enough to start with thumb pressure. Ideally just enough that the compression of the patch is enough to leave fabric impression on the ball. A single palm strike to the short starter that won't bruise the palm is sufficient. If you pick up some post fired patches and they are torn then some beveling of the crown can correct it by easing the start.
 

Grimord

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In the smaller calibers (36 & below), a faster twist is better for round ball use. Somewhere in the range of 1:30-1:36. As mentioned, it depends on the depth of the rifling.
 

hanshi

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For small calibers a twist of 1-48" or so is kind of a "sweet spot" as long as the rifling is decently deep. Small prb don't need the slow twist used for large calibers.
 

Coalforge

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Thanks to all. I knew 1:60 to 1:72 for the large bores but I would like to start shooting "Squirrel Gun" matches and am looking for an appropriate rifle. I was not sure about the smaller caliber rate.
 

Spence10

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Thanks to all. I knew 1:60 to 1:72 for the large bores but I would like to start shooting "Squirrel Gun" matches and am looking for an appropriate rifle. I was not sure about the smaller caliber rate.
I have a rifle with a .30 caliber Bill Large barrel, the twist rate is 1:56. It's very accurate, <2.5" groups at 100 yards.

Spence
 

M. De Land

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It doesn't take much of a spin to stabilize a ball and generally the less pitch the less fouling which is an important consideration on small caliber muzzle loaders with light rifling, in my opinion.
 

RAEDWALD

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Due to the increasing distance of the mass from the centre, small balls require a faster twist than larger ones. Thus a .32 should be in the 1:30ish region whilst an 8 bore will be happy with 1:120 or less. The need is for a level of rotational momentum which can either be small spun fast or large spun slow. Forsyth recognised that the ability of a large ball to accept a slow twist meant that one could use a larger charge without the ball stripping on the rifling yet get decent accuracy. Thus Forsyth style rifling only comes into it's own in 20 bore or above.

So the answer to the OP is that, in these smaller calibres, the common 1:48 twist is marginal but workable but a 1:30 is probably more suited to .32 or similar. So faster than 1:48 but slower than 1:30. What the faster ones will do is still stabilise the ball with lesser charges. In effect giving the same revolutions per second. You get the same RPS from a slow ball spun fast or a fast ball spun slow and RPS governs the stability of a ball in flight (ceteris paribus). In a conical the same principle applies but the variables are far more complex than that with which my hard of thinking brain can cope.

BTW, for the terminally bewildered like myself, faster means a twist with a lower number and slower the converse. Not absolutely intuitive.
 

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