What twist should I get

[andym79]

Hi guys, I am having a rifle re barrelled, I want a 1:12" really but that isn't an option unfortunately.

The twists available to me are 1:10 or 1:14.

The bullets I plan on using are as follows:

311041, 311407, 311446, 311291.

The longest is 1"

I would prefer to shoot these at 1000-1500 fps

Stability calculators suggest I can take these bullets down to 750 fps before they loss stability, so in theory I want a 1:14 kinder on the cast than a 1:10.

But does anyone have any real world experience of shooting bullets in the 150-180 grain .850-1" range at these sort of velocities in a 1:14 twist?

If so how slow could you go before you lost stability?

My only current 30 cal has a 1:10 barrel so I can't do the experiment myself.
I know the 1:10 would do it easily, but if I want to push hard the 1:10 will be hard on the bullets!

I need to let the smith know next week which twist to go with, I want the 1:14 but I haven't got the confidence without some empirical evidence to say go for it. The 1:10 is a safe bet but the 1:14 could be better.

Any advise greatly appreciated.

[country gent]

I can remember several makers offering 1-12 blanks in 30 cal Krieger, Douglas come to mind several even offered 1-11 as a "go between for service rifles. What makers blank are you looking at?

[andym79]

I know that several companies manufacture 1:12 and 1:11 twists. But down under options are limited, if you want a profiled barrel, you may have to wait a year! So for my benefit please assume only 1:10 or 1:14 is available.

[Kitika]

I've been contemplating the same thing. But I want to shoot 1 inch projis at about 2000fps or maybe slightly faster if I can. I'm leaning towards the 1/14 twist as all the calculators and threads I've read say it will be stable. How much are you looking at for the new barrel if you don't mind me asking?

[andym79]

$350 including profiling and bluing of barrel.

I can get a blank in 1:12 but then buying it and getting it profiled after will cost heaps more.

[NC_JEFF]

If your shooting cast Boolits only then I'd go with the 1:14, that gives you the option faster cast bullets if you ever want more fps. The speeds you listed will work with both twist rates. If your ever going on shoot j-words then I'd get the 1:10. I shoot cast in a 1:10 '06 barell at relatively slow to moderate with good results.

[44man]

I have not found twist rates harder on a boolit so all you should look for is fit and the distance you will shoot most. Closer ranges will favor a slower twist.

[Kitika]

44man is there a way to determine the optimum twist rate for certain ranges or is it a try it and see type of deal?

[Larry Gibson]

I have a lot of experience with the 311041, 311291, 311466 and the 30-165-FN XCB in 10, 11, 12, 13, 14 and 16" twists. You might do a search on the RPM Threshold. Also consider the cast bullet match shooters of yesteryear and still today use 14" and 16" twists in .30 - .32 caliber rifles with PB's cast bullets. I suggest you get the 14" twist barrel. It will stabilize those bullets just fine at the lower end mentioned and you will be able to shoot them (in a .308W with a 24 - 26" barrel for example) upwards of 2500 fps with excellent accuracy.

Here is what can be done at 2600+ fps. This is not a one time group as 10 shot groups with this load average under 1 moa to 1.5 moa. Note the velocity. My Palma rifle is a .308W with a 27.6" barrel with 14" twist. This is not the smallest group fired with that load btw. My Lyman 311041 at 2450 fps does close to the same.

Larry Gibson

191551

[Kitika]

Do the groups open up significantly at longer range Larry? Say 500-600yd with the 14" twist in your experience?

[Larry Gibson]

Not really, I've shot the load shown above to 500 yards and it held 1.5 moa for 8 out of 10 shots. The other 2 shots sretched to to 2 moa. The 30 XCB at 2600+ fps holds sub 2 moa to 600 yards. Clays sitting on the 300 yard berm (315 yds) are easy to hit.

Larry Gibson

[44man]

Sounds awful good to me. As you know I favor revolvers with faster twists because of velocity limitations for spin. I have just started with a few rifles.
But you can't beat what Larry has done.
It is all trial and testing, now if we can get an 06 to shoot that well.

[Hick]

I can attest to what Larry is saying. I had read some of his posts in the past and decided to dedicate my 32 WS Model 1894 to cast, just because of the 16" twist, while I shoot both cast and jacketed in my 30-30. Just about everything I've tried in the 32 WS works well-- with and without gas checks and with several different lubes.

[andym79]

So as I suspected the 1:14 is the go?

And there should be no stability issues so long as I use those or shorter bullets?

[Larry Gibson]

So as I suspected the 1:14 is the go?

And there should be no stability issues so long as I use those or shorter bullets?

Correct.

Larry Gibson

[Digital Dan]

Andy, not to dispute good advice already provided, but I do have some experience with a recent build for a 12" twist .30 cal barrel. It was built by Bullberry for a Contender. I don't know who supplied the blank but I'm sure the would tell you who their suppliers are.

The barrel was was put together with express intent to shoot 180 gr RN cast at subsonic velocity. I find it very accurate at velocities over the range of 700-1100 fps using 30:1 alloy. MOA with a red dot sight...even a caveman could do it.

[andym79]

Reinforces that a 1:12 as I suspected would be sweet, but also confirms that a 1:10 whilst working well, especially for longer range, isn't necessary!

[andym79]

I found this website which provides what is in my opinion a more useful representation of twist and stability that the usual calculator http://www.geoffrey-kolbe.com/barrel_twist.htm

I got these charts from that site:
191594
311407

191595
311291

191596
311407

191597
311406

191598
311299

These graphs in my opinion give a good representation that unless I want to shot bullets like 311299 a 1:14 twist should doing, with the exception perhaps at the lower end of the sonic region (avoid 1050fps?).

Taking the charts as gospel with a velocity of 1300fps or greater a 1:16 would even work, I shouldn't be surprised, doesn't the 32-40 shot 200 grain bullets from a 1:16 twist?

[Shiloh]

My 1:10 seem to stabilize cast just fine. 1800 is as far as i have worked up loads for accuracy. Taken them to over 2000 with no leading.

Shiloh

[Larry Gibson]

Sounds awful good to me. As you know I favor revolvers with faster twists because of velocity limitations for spin. I have just started with a few rifles.
But you can't beat what Larry has done.
It is all trial and testing, now if we can get an 06 to shoot that well.

Actually, if rebarreling you can get an '06 to shoot that well and that fast. Same suggested 14" twist with a 26" barrel using slow burning powders (4350, H4831, RL19, etc.) you can push the same NMT 1" long cast bullets from 700 to 2500+ fps. longer 1.15" bullets will stabilize at 2000 fps +/-. and if you want to shoot long range then with a decent bullet anything above 23 = 2400 fps keeps you trans sonic out to 600 yards.

It's about controlling the RPM. Consider the 311291 (one of the OPs selected bullets) many if not most that shoot that bullet in the '06 with 10" twist barrels have a real hard time maintaining any accuracy above 1940 fps. The RPM there is about 140,000. If we have an '06 with a 12" twist we can maintain accuracy to about 2300 fps or, again, just about 140,000 RPM. With a 14" twist '06 we can push the same 311291 to 2500 fps at a little under 140,000 RPM while maintaining the same level of accuracy that we could only get at 1940 fps in the 10" twist '06. Those are not precise figures because there are other things that come into play the faster we push cast bullets. However, they give us the idea. Now I'm holding moa accuracy with a 16" twist 30x60 XCB (a short chambered '06) with the 30 XCB cast of #2 alloy bullet at 2900+ fps.

Yes we can make an 06 shoot like that, just not with a 10" twist is all.

Larry Gibson

[44man]

Well, found out why the new Savage was not shooting, it was Joe with a different pressure on the gun. I shot it and shot some good groups, cast running around 1" at 100.
When we tried my home made lead sled it was much worse, the thing bounces and throws the gun. Those things need bolted down.
The 165 Hornady shot very good with 4350 but Joe hates the recoil, he is skinny.

[Larry Gibson]

I found this website which provides what is in my opinion a more useful representation of twist and stability that the usual calculator http://www.geoffrey-kolbe.com/barrel_twist.htm


Taking the charts as gospel with a velocity of 1300fps or greater a 1:16 would even work, I shouldn't be surprised, doesn't the 32-40 shot 200 grain bullets from a 1:16 twist?

Yes the 16" twist in a .30 caliber does work extremely well stabilizing bullets under 1". That is what my 30x60 XCB rifle has; a 31" long Palma contour Broughton 3 groove barrel with a 16" twist. However, you the OP stated you have a 10 and 14" twist available and asked which of those would be best with the cast bullets he mentions. The 14" twist is your best choice, and not a bad overall 30 caliber twist for cast bullets at that.

Larry Gibson

[andym79]

I wasn't saying I had to get a1:16 just surprised it would stabilize all of those bullets.

[Larry Gibson]

Andy

My bad, that came out wrong. Was just trying to give you the 16" twist barrel info I use. I must not have drank enough coffee.......my apologies.

Larry Gibson

[andym79]

That's okay. I was just trying to clarify.

I am coming to think more and more that twist rate especially with cast is very important and that too fast might not be a problem with jackets but it is with cast.

The rpm threshold is real the Swede taught me that and since I am only becoming more sure. That's a big reason I think the the 32-40 and 38-55 shot well with cast. I know my 38-55 will out shot my 30-30. In part because the big bullets are easier to make good ones but the twist of 1:16 vs 1:10 sure makes a difference.

[centershot]

"In part because the big bullets are easier to make good ones but the twist of 1:16 vs 1:10 sure makes a difference."

Amen to that, brother! :)

[Larry Gibson]

The larger the diameter of the bullet the more mass it has from the center of it's axis of rotation. Thus it has greater rotational velocity at a given rate of spin (RPM) than does a smaller diameter bullet at the same rate of spin (RPM). Only a certain amount of rotational velocity is required for stabilization. To have an equal factor of stabilization (Sg) the larger diameter requires less RPM (lower rate of spin) than does the smaller diameter bullet.

Yes it can be confusing......:veryconfu

Larry Gibson

[dondiego]

I have the same question regarding the 5.56. I have the option of getting a 1:9 twist or a 1:14 upper kit. I was planning on shooting cast at 55 grains and was leaning towards the 1:14 twist.

[C. Latch]

Just FWIW, playing with the stability calculator, a 14" twist should stabilize some 150-grain BT or 165-grain FB .308" projectiles...even a 180-grain round nose, at .308 velocities......perhaps not perfect stabilization and fully realized ballistic coefficient, but certainly stable enough to get decent accuracy. Jacketed bullets tend to be pointer and less dense (copper jackets, less dense than lead) than similar weight cast projectiles.....point being, the 1-14" should easily shoot not only your desired cast projectiles, but also light to medium weight jacketed projectiles.