twist rate limits

[jmorris]

The slowest twist I have is 1:48, Muzzle loader.

The fastest is 1:7, using old Speer thin jacket hollow points (intended for 1:14 barrels) they come apart due to the centrifugal force upon exiting the 1:7 barrel.

With a 1:14 the bullet is spinning around 175,000 RPM with the 1:7 it’s closer to 350,000 RPM (3400 fps bullet velocity)

 

[Jim Watson]

If a real US Springfield trapdoor, there is a good chance the barrel groove diameter is greater than modern SAAMI .458" and about anything can happen. My neighbor the gunsmith got a Trapdoor to shoot well with bullets out of a Lyman mold but the window of good loads was narrow.

 

[Demi-human]

1-6 is fairly common in some applications, i remember someone saying they had a custom rifle with a 1-5, ill see if i can find the post later.

I believe @mcb had a blackout in 1-3 or 1-5.
And the aforementioned 8.6 Blackout in 1-3.

I just received an ad from a store selling Cadex Arms rifles. The one that caught my eye was the 50BMG in 1-5 twist. That seems crazy fast.

 

[mcb]

Yeah my 5-inch 300 BO is a 1:5 twist. It works well with sub-sonics but I have not tried it with supers yet. I was nervous that 1: 5 was going to cause my favorite Maker Rex bullet to open in flight or worst in my suppressor. But that has proven to be an unrealized fear so far.

I have heard stories from a friend of Lehigh bullets opening inflight when fired in a 1: 3 twist 300 BO barrel. Not sure exactly which bullet or velocity but he said they would open in flight make funky noises and they found them on the ground in front of the 100 yard backstop.

 

[Archie]

Then why does my 45-70 start losing accuracy if I push a 500 grain bullet faster than around 1300-1400 FPS? A 1-22 twist is about as slow as one can go in a 45-70, shooting 500 gr. bullets. Pushing them faster only degrades accuracy. I know this from actual range experience.

I suspect the higher velocity with a more or less flat fronted bullet creates more air resistance and therefore the bullet is subject to yawing. Not really directly related to twist rate. A spitzer shape bullet (if such exists) might help. Or the loaded cartridge would be too long to work in the action.

 

[Archie]

8.6 Blackout has 1:3 twist. Long heavy bullet moving slowly requires fast twist.

I looked that up prior to objecting. No objection, seems to be correct. Barrel strikes me as being rifled with a tap.

 

[PRD1]

The great British engineer and inventor, Sir Joseph Whitworth, in his experiments for improving rifle accuracy, tried virtually every rifling pitch down to and including 1:1", and every rifling pattern then known. His final design for what became known as the Whitworth rifle and barrel design in what was then termed 'small bore' was the nominally .451" caliber hexagonal bullet and rifling with a pitch of 1:20", for use with a paper-patched lead alloy bullet of about 480 grains weight. It was and is among the most accurate of muzzleloading rifles, though others with more conventional rifling patterns can perform as well.

PRD1 - mhb - MIke

 

[Jim Watson]

Sir Joseph was working with the same bullet weight and powder charge as the .577 Enfield, just more efficiently out of a smaller bore.
The Whitworth hexagonal bore had a short working life, maybe five years. By 1865 other rifling plans had taken the lead in the small bore rifle matches. Pedersoli sells a pretty good reproduction of the Gibbs target rifle, along with a Whitworth and what they call a Volunteer Target rifle, each with different rifling plan. And then the .577/.450 Martini-Henry got the distinctive seven groove Alex Henry rifling.