45-70 barrel confusion

[oops]

Hi to all!!

I am a bit confused about barrels for a 45-70.If I want to shoot nothing but black powder in the gun,how do I pick the twist and barrel design for that(number of grooves and lands,depth of rifling....)...And is it the same for 45-90,45-110,45-120

My thoughts are on a cast bullets only.....possible duplex loads.....32"ish barrel.I keep finding to many choices...Point me to the light CGN'ers

P.S.....This will be a built rifle

 

[delta1]

1 in 18 inch twist will handle most cast in the 45/70. Barrel design can go from round,half round/octagonal to full octagonal. Hunting barrel in the 26028 inch range long range rifle in the 30-34 inch.
Other's with more knowledge will chime in.

 

[mooncoon]

you pick the twist rate for the heaviest bullet you intend to shoot. The formula is 150 x diameter squared over length will give you the twist rate. Note that you can reverse twist and length to calculate the longest bullet that twist will stabilize. In practice most people make the twist 1" faster than the formula.

While I am sure numerous people are going to jump up and claim the formula (Greenhill formula) is not perfect, the point is that it is simple and does work which is much better than saying "well Remington uses a 1 : X twist in their sporting rifles or similar type of observations

cheers mooncoon

 

[Metman2]

...

While I am sure numerous people are going to jump up and claim the formula (Greenhill formula) is not perfect, the point is that it is simple and does work which is much better than saying "well Remington uses a 1 : X twist in their sporting rifles or similar type of observations

cheers mooncoon

I'd like to "chime in" that I think for the vast majority of us shooters who are not knocking over squirrels at 1000 yards, , Greenhill works remarkably well for such a simple formula.

 

[Papaclaude]

you pick the twist rate for the heaviest bullet you intend to shoot. The formula is 150 x diameter squared over length will give you the twist rate. Note that you can reverse twist and length to calculate the longest bullet that twist will stabilize. In practice most people make the twist 1" faster than the formula.

While I am sure numerous people are going to jump up and claim the formula (Greenhill formula) is not perfect, the point is that it is simple and does work which is much better than saying "well Remington uses a 1 : X twist in their sporting rifles or similar type of observations

cheers mooncoon

Hi Mooncoon - dumb question, but by length is that length of bullet or length of barrel?

 

[mooncoon]

Hi Mooncoon - dumb question, but by length is that length of bullet or length of barrel?

length of bullet. Dimensions are in inches. Greenhill was an artillery officer in the early 1880s I think and developed the formula for artillery projectiles but it works remarkably well with rifle size bullets as well. There are constants to use if the projectile is dramatically different than lead or jacketed lead but I don't have them and very few of us are shooting aluminum or depleted uranium slugs.

I have found it useful when I have acquired an antique rifle with a strange caliber because it tells me the largest projectile I can shoot out of that barrel. One that comes to mind in particular was a cape gun with one barrel in something like 476 express; 100 or more grains of powder and a little short 476 projectile. At the time made, they believed in light projectiles and lots of powder to get a flatter trajectory at long range

cheers mooncoon

 

[oops]

Other than twist rate based on bullet weight....how do I choose for rifling depth...do any barrel makers build for soft bullets or at least cast

 

[mooncoon]

Other than twist rate based on bullet weight....how do I choose for rifling depth...do any barrel makers build for soft bullets or at least cast

the twist rate is actually based on bullet length (which indirectly is weight). Barrels can be button rifled or cut rifled. Button rifling means that they are rifled by pulling a carbide cherry or button through the barrel once which more or less swages or crushes the rifling into the bore. That limits the depth that can be formed to about .004" Cut rifling is done by a series of passes with a broach which cuts the grooves a little deeper with each pass. On some custom barrels they can be as deep as .020" or more but .010" is probably far more common

If you are looking for deep rifling, you can begin by eliminating those barrels described as button rifled and would have to question the seller as to how deep cut rifled barrels are rifled to

cheers mooncoon