Calculating Twist Rate with Sabot?

[WaltWhite]

I'm using various calculators and equations to determine ideal twist rate for a projectile fired in a sabot. Some call for groove diameter (.50 or thereabouts) and some call for projectile diameter (.43). Using one or the other number gives a very different result. I wonder if anyone knows for sure which figure to use for sabots?

I have a PA Pellet with 1 in 48 twist and am trying to find a good sabot load. A gunsmith I trust said to try a 200 grain XTP at .44-40 velocity level (1000-1250). As it happens this seems to stabilize perfectly according to the numbers using groove diameter (.50), but the same equation says to push it at 2000+ for stability in a 1 in 48 assuming .43 diameter.

I imagine the actual diameter of the bore has an effect on all this just like the length of projectile, etc, but my brain isn't quite equipped to grasp the nuance.

 

[rcflint]

The twist rate not only depends upon the caliber, but more on the length of the bullet. The longer the bullet, the faster a twist required. Same reason you must spin a football to throw it, not necessary with a baseball..

Check to see what twist rate your chosen bullet uses when in the mother caliber cartridge.

 

[MEHavey]

The bullet could care less about groove diameter once set spinning.
Therefore use the bullet diameter in calculating required twist rate.

 

[rodwha]

*Im a bit slow it seems*

 

[CraigC]

A gunsmith I trust said to try a 200 grain XTP at .44-40 velocity level (1000-1250).

This is dumb. Firstly, the 200gr XTP is not designed for .44-40 velocity, it's designed for the .44Mag. With a slower twist rate like 1-48", you need all the velocity you can get. At the velocities you'll get from that rifle, it's a poor choice anyway. Use the heavier, proven bullets (240-300gr) and push them with full loads. Test to see how they fly. I'd be tempted to try the 270gr Speer. They're toughly constructed but should expand nicely at the elevated speed.

 

[rodwha]

Hornady states the 200 grn .44 cal XTP is designed for 750-1650 fps.

I'd prefer a bit more velocity too though, as well as a heavier bullet.

 

[DD4lifeusmc]

why use a sabot in a muzzle loader in the first place?
The bullet being smaller has to have a higher velocity to have the same impact energy than the bigger heavier one in the first place.

Technically the smaller projectile isn't going to spin any faster than what the sabot is spinning to begin with. and when the sabot leaves the bullet, not going to matter a whole heck of a lot anyway.
Jmo

 

[WaltWhite]

I use sabots in a ML for a variety of reasons. They're easier to load, modern design, accurate and I can shoot the bullets in my .44s and .45s. Those would be the top reasons. I also get extremely tight standard deviation with them. If you have a magic bullet I should try instead and its not a pain to load I'm all for it. IMO traditions really shorted the PA pellet with a 1:48 twist. Trying to make the best of it.

FYI the hard bear bullets like the deep curl 270 Speer = pass through with no expansion on the size deer I'm shooting. A 120 grain 777 charge will push a 300 grain Sierra jsp at 1660 and even at that speed it won't reliably expand. Ask me how I know.

 

[Loyalist Dave]

The problem is when folks use a modern bullet with an antique propellant, and can't get the performance from those modern bullets in the same manner that they get with a modern propellant and the modern velocities. No matter what the folks who make money selling the modern bullets tell you.

YET...antique bullets, and obsolete cartridges have accounted for lots of large and/or dangerous game.

I mean if I can hammer an East coast whitetail with a 225 grain, all lead round ball launched with merely 70 grains of 3Fg, out at 100 yards, you guys should be out performing me with a heavier bullet and a much heavier powder load, when shooting your inlines, right?

So have you thought about using a 250 grain lead alloy or even all lead .45 caliber cast bullet, or perhaps even a 300 grain .45 caliber lead alloy or all lead bullet in your sabots? Lee molds are available for either weight, but you should be able to find CAS bullets in .45/250 lead alloy. So you'd be sorta duplicating an old "buffalo" cartridge???

LD

 

[mac_hunter870]

45 Cal .452 225 gr FTX® (45 Colt)

This is the bullet I shoot, using sabots and two 50 grain Pyrodex pellets, from a CVA Staghorn Magnum 24" barrel .50 caliber with a rate of twist of 1 in 32", topped with a fixed 4X Simmons scope. I have never recovered a bullet that I shot deer with. I've shot them as close as 30 yards and as far out as about 125 yards with this set up and it blows through them cleanly with a good size exit hole which tells me that at either distance they are expanding and performing as designed and within the recommended/required velocity ranges. I didn't over think this (do a bunch of math) when I picked the bullet. I picked it because of the performance I saw when shooting deer with .45-70 Lever Evolution factory loads out of my Marlin 1895. Just my $0.02.

 

[ironworkerwill]

So have you thought about using a 250 grain lead alloy or even all lead .45 caliber cast bullet, or perhaps even a 300 grain .45 caliber lead alloy or all lead bullet in your sabots? Lee molds are available for either weight, but you should be able to find CAS bullets in .45/250 lead alloy. So you'd be sorta duplicating an old "buffalo" cartridge???

I like it! I also like Maxi-balls as they, IMO, are just as easy to load as sabots and one less thing to worry with. I used 90gr of AP with the maxi's and were squirrel huntn accurate at 40 yards. I also tried 777, Pyro, and Black. All loose powder shot well, the pellets... not so much.