12 bore rifle twist rate

[Mulemauler]

Found this
http://kwk.us/twist.html

Very cool! Thank you for posting it.

 

[Blackpowder8bore]

Sorry I dont have the knowledge on that one.
Basically the twist required is related to the bullet length and the velocity. I believe the formula is hiding in Google somewhere.
As @bubba.50 said 1:28 seems quick but a modern 12g slug rifled barrel has a 1:36".
Reality is velocity is unlikely to exceed 1200fps and more like 1000fps. However if it is built as a late percussion rifle with high pressure breach then maybe you could push it.

The normal 12g slug is either 350grain or 440 grain so pretty light but as it is hollow based it is longer than a PRB.
For a 12g the PRB would be 550grainish so a 700gr is not really a heavy bullet.

How long is the bullet compared to a modern 12g slug?

The bullet is maybe a 1/3 of an inch longerthan the round ball,not enough to matter.ive lesrned maybe 1in66 is a fine twist for 700gr bullet. I might can push the prb 555 grainsto 1400fps with 250 grs of 777 and magnum perc caps,you think?

 

[Blackpowder8bore]

Very cool! Thank you for posting it.

Excellent informative calculator!

 

[Bad Karma]

The bullet is maybe a 1/3 of an inch longerthan the round ball,not enough to matter.ive lesrned maybe 1in66 is a fine twist for 700gr bullet. I might can push the prb 555 grainsto 1400fps with 250 grs of 777 and magnum perc caps,you think?

Please post video... best of luck!

 

[Blackpowder8bore]

I had a Purdey 12b rifled single shot in the early 2000's. I can't remember if the twist was 1:70 or 1:90. The conical was hollow-based and weighed 430 grains. It did not use a patch, it was a full-bore conical. I only measured velocity with a chronograph once and it showed 1240 FPS. I used 100 grains of powder. At the time I had no idea how much powder to use and I picked 100 because that is what I saw as a common charge for black-powder projectiles. The fixed sights were a tad high at 50-yards with that load. 1:28 rate is quite different. A 700 grain projectile is quite heavier and 225 grains of powder, that sounds excessive. What does the barrel maker say? I think that is the person to answer your question.

Thank you for your input. Good idsa thd barrel maker says 1in66 should be good for what i want to shoot. I wanted other opinions too.The standardfor their 12bore builds is 225-250 grains of powder with a 550 grain patched roundball. It is excessive but is designed for felling large animals so j get it. But i dont have to use the max. I think its very interesting you got a 400+ gr projectile to 1240 with only 100 grs powder.it sounds good.

 

[Blackpowder8bore]

Many English gunmakers of the mid 19th century found that with heavy charges big bore rifles could only stabilize a heavy bullet with VERY slow twist. 1-90 to 100 seemed to work well. With faster twist to prevent stripping they had to use low powder charges. African hunters of the time complained that while they were accurate with the light charge did not have enough power to penetrate really big game.

Excellent!! Thats probably why the barrel maker said 1in66 should be good for what i neeed. Thats really good information.

 

[shorthair]

Sounds like great fun.