What twist for .50?
 

Well, I finally decided I'm going to order a custom .50 barrel for my Pro Hunter from SMI. I sold a few guns and was going to try to get started in bowhunting, but I don't think I would like shooting a bow as much as much as a gun. I was (and still am a little) hesitant to spend the money on a custom barrel, but finally just decided it's a one time thing and might as well do it and have fun with it.
So, I can order about whatever twist I want. I read where guys have gone with as fast as 1 in 22" to as slow as 1 in 32", which is the SMI standard twist. I plan to shoot 250 to 300 gr. primarily but I'm sure I'll shoot some lighter and some heavier. The 300 gr. SST's I have are exactly 1" and using the Greenhill formula I would actually want something close to 1 in 35" but that seems too slow. I was thinking 1 in 24" but really don't know.

FWIW, I wonder if that formula is applicable to sabots. The sabot is what is gripped by the rifling and imparts the spin to the bullet. Just thinking out loud.

I wondered the same thing. I did try it with a 45 bullet, and it's only a couple turns faster.

Every twist is a compromise. I think the 1 in 24 twist is a good one in a 50 for longer bullets. That twist can shoot shorter saboted bullets as well. Sabotloader has proved this. The 1 in 28 has been used a lot and shoots very accurately also. I would go with one of those two and I would lean towards the 1 in 24.

Well since i own a Douglas 1-32, a Savage 1-24 and have owned numerous 1-28s, i can say you probably wont see a difference unless you try shooting light weights in the 1-24. My 1-32 shoots 225gr-275gr 45cal bullets (Including Barnes) with exceptional accuracy. Ive even shot the 325gr FTX with "ok" results.

That being said i would likely go with a 1-28 if i was ordering a custom twist just because it works good with the largest variety of bullets and probably even powders. One things for sure my 1-32 LOVES the 225gr 45LC XPB and so does my shoulder at SML speeds in the NULA.

I would have thought the 1 in 32 would have been to slow for the lighter 225 gr. I have a couple different varieties of 225's that I was hoping to shoot.
I was actually just thinking that I might go with 1 in 26". I don't know if it's just because it's half way between the two extremes or something else, but for some reason it seems like a good choice.
Any reason it wouldn't work?

I think you got it backwards.

A heavier bullet usually prefers a faster twist. The 1-32 shoots the 45cal 225gr Barnes and XTP VERY well even at over 2300fps. The Savage's 1-24 usually doesn't like to shoot light weights that fast. I pretty much only shoot the 325gr FTX in my Savage and sometimes the 275gr XPB made for 460S&W.

I think you're right, don't know what I was thinking.
Perhaps then I would be best off just going with the 1 in 32" and figure if that's what he usually builds his barrels in than he probably knows what he's doing.
I don't think I'll shoot anything lighter than 225 and probably not anything heavier than 325, maybe 350. Should work, right?

It should work fine. Mine is a Douglas 1-32 on the NULA and even though i was skeptical, the first range day removed all doubts. Recoil was pretty stiff with the 325gr at 2196fps but wasn't bad with the 225gr-275gr slugs.

On MM there is some load data for both SMI and NULA Douglas barrels including an Encore or two. It appears most of the common deer hunting bullets do just fine. The 225gr XTP bullets are my fun bullets and cheap too.

I would order it in a 1/26" barrel.

If i was you i would seriously consider a 45 barrel over a 50. Like everyone said, your not going to see much difference in your twist rates in the 50cal. A 45 in a 1/20 twist opens up a lot of new opportunities for you.

If I'm not mistaken most inlines are 1-28...My Knight is anyway...I'd have to stay with that...

You are talking about a gun mainly for sabots, correct???

It will be mainly for sabots. At this point sizing and shooting sabotless doesn't have a lot of appeal.
It looks like Douglas barrels in .50 can be had in 20, 24, 30, 34, and 36. So if that's the case my options that I would consider most are 24 or 30, and I'm probably leaning more towards the 30. I need to talk to Ron at SMI again and see what I can find out.
Grouse, I thought long and hard about going with .45. In the end I decided that I have exactly 10 .45 bullets and boxes of .50. If I had more 40 bullets and 45 sabots around I would go .45 for sure.

There are a couple of things that can fine tune the twist. one is the exact caliber of the bullet the other is the velocity coming out of the muzzle.
I ran a few through the Greenhill program to demonstrate what I am talking about , and to deal with some misconceptions what regulates the twist is a combination of length and diameter weight has nothing to do with it but velocity does it is one of the controlling factors.
A .458 dia. bullet with a velocity of 1800 and a length of 1 inch is an exact match with a twist of 31 per inch.
a .450 dia. bullet at a velocity of 1800 with a length of 1 inch is an exact match with with 30 per inch.
a 430 dia. bullet with a velocity of 1800 is an exact match of 27 per inch
now if you increase the velocity it reduces the twist if you lower the velocity it requires a faster twist.
A 40 caliber bullet traveling 1800 fps 1 inch long exactly matches with a twist of 24 but a 40 caliber bullet 1 inch long traveling 2800 fps exactly matches a twist of 24.
One of the things you need to remember about this is that a bullet that is under stabilized will wobble and turn end over while a bullet that is over stabilized has a 15 % tolerance before it becomes unstable.

Thanks for that. It helps explain things some. My only question is where you wrote

"now if you increase the velocity it reduces the twist if you lower the velocity it requires a faster twist.
A 40 caliber bullet traveling 1800 fps 1 inch long exactly matches with a twist of 24 but a 40 caliber bullet 1 inch long traveling 2800 fps exactly matches a twist of 24."

I'm going to assume that one of those is a misprint, though it's possible I'm just reading it wrong. But I would assume the same bullet at faster speed would require the faster twist?

But then I was think I would be better to go with 1:24 twist than would be to go with a 1:30.

One more thing you may want to consider. Im not sure which Douglas barrel SMI uses but.....

Douglas offers Premium XX grade and Premium Air Gauge barrels too. The Premium XX is what Melvin uses on the NULAs and is well worth the extra IMO. Its only $10 more and if you have to wait for a custom twist....why not get a Premium XX grade.

As far as a 1-24, its probably fine in a quality barrel. Some OEM Savage barrels left a little to be desired due to rough tooling. Mine seems fine but it certainly isnt in the same league as a Douglas or a Pacnor.

why not just buy a 1:20 twist 45-70 Bergara or TC barrel and have it converted?

Probably because he wants a 50cal. Atleast for his first SML. ;)

Kirby, it is not a miss print that is correct. You are beginning to understand some of the variables involved.

Thought about it a lot yesterday. I do believe I'm just going to go with the 1:32. It was pointed out to me that people smarter than I probably already put a lot of thought into it before choosing this twist for their barrels. It was the best choice for SMI and NULA, I don't see any reason I should change it. I may ask about the premium barrel. At this point, what's $10?

As for the Bergara barrel, the reason I'm not going that route is that I'm not completely sure I can make it work with a ramrod on the barrel, something I really want. Also Bergara barrels aren't set up for open sights. MN says I have to hunt with open sights during ML season. The cheapest I can find to have the barrel drilled is $30/hole. I also don't have any .45 stuff, so by the time I get the sights on and buy some bullets and sabots and all that stuff, I'm only saving a little.