twist ????

[J.D.]

Well, there is a lot of hoopla, in this thread, about rates of twists. In the 40 plus years of tinkering with these old pieces, I have found that about any twist will shoot round balls well if the powder charge is adjusted to match the characteristics of the barrel.

For example, An acquaintance has a .32 with a 1:70 twist that shoots like a house afire with something approaching 50-60 gr FFFG, though I don't remember the actual charge weight.

Another has a 50 or 54 with a twist rate of about 1:90 that shoots RB like no other barrel I have seen, at long ranges, with heavy charges.

The upshot of all of this is choose a caliber and ROT for the activities you plan for your piece, find the most accurate load, and shoot the daylights out of it.

God bless

 

[longcruise]

J.D., good advice for any beginning round ball shooter.

For a dedicated round ball gun nobody will go wrong by selecting a barrel from any of the well known makers with that maker's "round ball twist" deemed appropriate for the caliber.

 

[David W.]

J.D., good advice for any beginning round ball shooter.

For a dedicated round ball gun nobody will go wrong by selecting a barrel from any of the well known makers with that maker's "round ball twist" deemed appropriate for the caliber.

That is exactly the point I am trying to get across. Why confuse a newbie with mathimatical formula's that do not mean everything. Go with a good quality barrel intended for a PRB and the heck with everything else. I happen to like Colerian's round bottom rifling. It makes cleaning much easier and they are noted to be able to acheive darn good accuracy. It really does not matter what brand though, just buy American! I am sure a few Americans would like to hang on to their jobs.

 

[Zonie]

The Greenhill and Miller formulas are fine for elongated bullets but have little or nothing to do with roundballs.

Elongated bullets require a spin to stabilize them. Without it they will yaw, often turning end for end as they fly downrange.

Roundballs on the other hand are inherently stable as far as developing rotations other than the one imparted by the twist of the barrel.

A roundball is not perfectly round. Often there are small depressions and irregularities on the surface and at high velocity the wind acts on these features often deflecting the ball from its intended path.
Imagine a small lump, located off of center on the forward surface of the ball.
The high speed wind hitting this will create a pressure unequal to the pressure elsewhere on the ball and this pressure will deflect the ball.
This happens when a roundball is shot out of a smoothbore gun, and explains why at short ranges where the length of time is very short a smoothbore shooting a roundball can be quite accurate but at longer distances the ball may go in any direction from the point of aim.

If the ball is spun around the axis along the line of sight, these air pressures try to deflect the ball as before but because the ball is spinning, the deflection force is constantly changing its direction around the path of the balls flight. This in effect nullifies the unequal pressures force allowing the ball to travel in the intended direction with great accuracy.

Having said that, the larger mass of the larger calibers has the inertia to overcome the unequal pressures mentioned above so, it can work well with a slower rate of twist.
The smaller mass and smaller inertia of a small ball needs a faster rate of spin to nullify the effects of the unequal pressures.

This explains why, generally speaking the barrel manufactures use faster rates of twist in the smaller calibers.

A fast rate of twist can be used for the larger calibers, for instance the 1:48 twist of the original Hawkens (and the TC Hawkens) works quite well with a .50 and even a .54 caliber gun shooting a roundball but generally speaking it requires the deep grooves of a roundball gun (or very tight ball/patch combination's) to use large powder loads when this rate of twist is used in the big bores.

 

[trapperdan2061]

Wow lost to consider but the out come is a Green mountain 1 in 70 they seem to be the fav, when it comes to barrels, now to get one in Canada.

Thanks All

 

[David W.]

Wow lost to consider but the out come is a Green mountain 1 in 70 they seem to be the fav, when it comes to barrels, now to get one in Canada.

Thanks All

You can not go wrong with a GM!

 

[mr.flintlock]

I will share with you a formula that I have used for years and it actually seems to work. Now, bare in mind that this is using 3-f black powder ONLY with patched round balls, which I use in all of my rifles ranging from 32 to 62 calibers and every one in between.This formula is used with a volume powder measure.

It is calculated by using the rate of twist and the caliber.

caliber X rate of twist
___________________________
2



Example: 54 caliber barrel with a 1/70
rate of twist.


.54 X 70
___________ = 75.6gr of 3-f
2

This will get you in the ballpark and you
can then fine tune the load for best
accuracy.

While this is not an exact answer to your question, It may help you determine a good starting load for which ever barrel and twist that you choose.


2

 

[Dphar]

I will share with you a formula that I have used for years and it actually seems to work. Now, bare in mind that this is using 3-f black powder ONLY with patched round balls, which I use in all of my rifles ranging from 32 to 62 calibers and every one in between.This formula is used with a volume powder measure.

It is calculated by using the rate of twist and the caliber.

caliber X rate of twist
___________________________
2



Example: 54 caliber barrel with a 1/70
rate of twist.


.54 X 70
___________ = 75.6gr of 3-f
2

This will get you in the ballpark and you
can then fine tune the load for best
accuracy.

While this is not an exact answer to your question, It may help you determine a good starting load for which ever barrel and twist that you choose.


2

Rifling twist has very little to do with how much powder most common bore sizes will work well with. A 48" twist will shoot just as much powder without stripping as a 72 in the 45-58 caliber range.
But this can be effected by ball size, patch material and thickness and the lube used.
Some barrels may like heavy loads some might light lighter loads.
I had a 72 twist 54 once that would not shoot well enough to hunt with with less than 120 gr of FFF.
I had a 48" 50 that was very accurate with 90 fff.

Dan

 

[Zonie]

Dan, I didn't see where mr. flintlock said anything about stripping a patch.

The way I read it, he was giving his formula for a good starting place for a load that considers the rate of twist and the caliber.

I am somewhat surprised that you didn't mention the depth of the rifling as something that has an effect on powder loads and stripping.

IMO, the biggest downfall of some of the fast twist barrels, when shooting a patched roundball, is the very shallow rifling that many of them come with.

 

[Walks with fire]

.54x70x2=75.6

.54x70/2=18.9

 

[David W.]

.54x70x2=75.6

.54x70/2=18.9

You and I are using the same math. However, it's been a long time since I was in public school!

 

[nkbj]

I'm waiting on my .577 barrel with 1:48" twist.
The parts are accumulating, piece by piece, giving me something to do while waiting on the barrel.

 

[mr.flintlock]

Walks with fire, Thank you for that correction. I did gave an incorrect formula. And to everyone, My formula is Bore size X rate of twist X 2.

Example .54x70x2= 75.6gr of 3-f with PRB.

Real men admit their mistakes and I made one when I posted the first time.

 

[Walks with fire]

We both knew what you intended and it wasn't until I started to try different twists that I discovered the error. :thumbsup:

 

[trapperdan2061]

Walks with fire, Thank you for that correction. I did gave an incorrect formula. And to everyone, My formula is Bore size X rate of twist X 2.

Example .54x70x2= 75.6gr of 3-f with PRB.

Real men admit their mistakes and I made one when I posted the first time.

so with this then

.50x48x2=48 so 48 grains of 2 or 3 F

RIGHT ??

 

[longcruise]

so with this then

.50x48x2=48 so 48 grains of 2 or 3 F

RIGHT ??

My exp with .50 cals in 1:48 don't bear this out. 48 grains might make a dandy starting point, but all (four) rifles that I have worked with ended up liking 65 to 75 grains of ff or fff. They all shot "ok" with 80 to 90 grains.

 

[mr.flintlock]

Not right. The formula that I gave was for 3-f only. I never mentioned 2-f because it takes less 3-f to do the same work of more 2-f. Lyman did some testing back in the 1970s with 2-f Vs 3-f loads and proved this. Using a 54 caliber barrel they used eight different loads ranging from 40gr to 180gr with PRB. In every case 3f gave a substantial increase in velocity over 2-f. These tests can be found on page 85 of the Lyman Black Powder Hand Book.

I once had a T.C New Englander 50.cal and shot 80gr of 2-f w/PRB but found that 55gr(not too far from the 48gr that you mentioned) of 3f gave me about the same velocity- and though it may seem like an anemic load to some, I killed deer cleanly deer with it.

This past season I used a 50cal with green mountain barrel with a 1-70 twist. I used 70gr of 3-f behind a PRB.I shot too deer with this combo and both deer dropped in their tracks.

When dealing with loads each rifle is a law unto itself. As I stated in my earlier post the formula is a good one as long as one uses 3-f powder and PRB. But yes, it is intended as a starting point and MUST be fine tuned for accuracy.