Barrel twist and bullet weight?

[PNW_Steve]

Hey Everyone,

I am looking at a .224 barrel for one of my AR's. I found one in stock that checks all of my boxes except for the twist rate.

I want to be able to shoot some of the newer high BC bullets well. The 1:6.5 twist is somewhat faster than I was looking at. It will certainly handle the longer heavier bullets but am I going to loose the ability to shoot 55gr bullets well.

I read something that said that too fast a twist should not affect accuracy. This runs contrary to what I thought. Then I started tinkering with the Berger twist/stability calculator. That seemed to reinforce the idea that faster twist barrels are not a problem with lighter bullets. Within reason.....

What is the reality?

Can I stabilize a (.224) 50grain bullet out of 22" 1:6.5 twist barrel at 2800fps+? With good accuracy? If I can't get MOA accuracy at 100 yards with 50-55gr bullets then I will do something else.

Thanks.

S.

[Harter66]

Good grief 1-6.5 " !
That 100 gr NOE should be happy in that .
I shoot the NOE 62 gr in a 222 @ 1-14" . The 8" specimens will shoot accurately down to 1200 fps I could have hand scaled below 2.5 gr of Unique but was shooting them for 22 LR replacements . The slow twist 222 gets 2600 fps MV , the faster 1-8 only allows 2050 fps MV . Same powder , primer , and bullet lot . Even with jacketed you'll be approaching centrifugal jacket failure at 2800 fps . I think an 1-8" with handle the 75s in VLD forms and 80 gr cast .

[Neverhome]

Not with cast!

But jacketed you should be good.
Heard plenty of stories of folks blowing up bullets in flight from over spinning. Minuscule jacket imbalances magnified by rotational speed. Seriously doubt that would ever be an issue at 2800 ft/sec. I’ve shot plenty of 6.5 120gr bullets at around 3200ft/sec out of an 8 twist and averaged sub minute at 300 yards. No loss of accuracy that I could tell. Sure sure 8 twist isn’t 6.5 but still

[Elroy]

It would just get a 1-8,and no faster. You will be able to handle most bullet weighing up into the mid 70s..You are gonna have to seat to no longer than 2.26"- 2.28" ,and a long enough bullet to justify a 1-6.5 twist is gonna eat up a lot of case capacity .

[Harter66]

310,154 rpm @ 1-6.5 ×2800.
300,000 rpm @ 1-12 x 4100 fps in 22-250 , the ragged edge of jacket failure for typical 50-55 22 cal bullets .

Just numbers for reference .

[Neverhome]

I just did that math for my example up there ^ and only get 288,000 rpm. So definitely a significant rpm difference and worth thinking about.
That being said, only thin jacketed varmint bullets go poof

[RU shooter]

Unless you wanting to shoot bullets over 80 grs stay with a 1:8 . You didn't say what cartridge your shooting im assuming a 223 ?

[PNW_Steve]

Thank you all for the great answers.

I have a 1:8 barrel on order. I am hoping to have it by the end of September. In the meantime I would like to get rolling on the build and shooting. Even if it is with a "temporary" barrel. I found an outfit that has one barrel in stock, at a reasonable price, and it is a 1:6.5 twist.

The cartridge is 22 Predator aka: .224 Grendel. I am hoping to be able to shoot the 88's.

I am leaning towards passing on the 1:6.5 barrel. What keeps me looking at it is my want to build and shoot this summer. There are not a ton of 22Predator barrels sitting on vendors shelves.

I wonder if 55's would play nicely with the 1:6.5? That would give me enough variety to shoot some premium loads and still be able to plink reasonably.

Anyone have a barrel stretcher handy? :razz:

[country gent]

I have 1-7s on my NRA 223 match rifles they do good with 80 grn bullets. I shot alot of he longer vld jlks at 600 yds. normally 75 grn hornadys at 200 and 300 yds. They do okay with 55s but you need to watch the jackets used. Sierra hornady jackets are thicker, berger JLK, and the upper end use J-4 jackets that are thinner and softer. Ive had berger 115 grn 6mm let go in my 243 when shooting 1000 yds. Its not just rotation but also rotation time jacket and core combination. I never "lost a sierra or JLK in the 243. The bergers would let go about 200 yds from the target. Scorer verified thats where the trace ended.

Buddy had a 1-6.5 in 223 for 90 grn bullets and 55s need t be loaded down some to lower rotation but were accurate. My AR 10 in 22-250 has a 7 twist on it and 90 grn jlks at 3500 stabilize but dont get below 2 - 2 1/2" at 200 yds. 80s will hit a 3/4" target paster regularly. Its very close to stabilizing the 90s at that velocity. On a good day ( for me ) it will hold a 1 1/2" spotter disk at 600 yds. Guys in the pots claim the bullet crack sounds the same as a 223 at 200 yds.

When figuring twist several things need to be taken into account. velocity range expected, bullet weight and length, distance expected to be used at. As distance is extended bullet velocity drops meaning it can become unstable at extended distance. While most rack grade M14s were 1-12 the high power shooter used 1-10 for 600 on out for the added distance.

[Harter66]

Cuties and grapefruit here .
I had an 06' with a 1-8.5 . With cast it's awesome under 1800 fps which made it a prime candidate for the 230 gr spitzer/BT 300 BO bullets . With a jacketed 150 the jump from 2680 to 2710 fps is a 1.25+ group growth at 2750 bullets at 50/100/150 yd were visibly tipped on impact and out to 5" groups . At 2800 fps MV groups were 8" round holes . At 2850 fps groups were passed 16" with lead smudge and abnormal holes . I'm not saying that the #3033 Hornady 150 SPBT was coming apart but it didn't display any of those tendencies in the available 1-10 and 1-12 barrels to 2900 fps .

[Winger Ed.]

I wonder if 55's would play nicely with the 1:6.5? :

They should.
The govt. speeded up the twist in the M-16 from 1:10 to be able to shoot/stabilize
heavier bullets than the 50s & 55s from the old days.
A down side is the more thin skinned & fragile bullets like Hornady's SX series will fly apart from the RPM spin speed
if you push them up much faster than they recommend, even in a 1:10.

Check out the data for 5.56 NATO.
Most books are using a 1:7 twist and starting their page with 55s.
Results with a 6.5 twist are going to be similar.

[Wolverine19D]

The original twist rate was actually 1-14 in the M16 but was quickly changed to 1-12 due to the 1-14 being on the edge of stability and causing issues in arctic testing. The 1-12 was in service until the early-mid 80's when they went to the 1-7 and the only reason they chose 1-7 was to handle the longer tracer bullets otherwise a 1-9 would have been fine for the new 62gr bullets.

To answer your question OP, the 1-6.5 twist will be fine. I have very limited knowledge on the newer 224 Valkyrie/ 22 Predator you mention but from the 5.56 world the 1-7 twist barrels will shoot 55gr bullets just as well as a 1-12 twist bullet. That doesn't mean your barrel will like 55's because every barrel is different.

You could have a dozen 1-7 twist barrels, and a dozen 1-12 twist barrels and on average they probably both will shoot the 55s about the same. The only time you will have a problem with the faster twist rate is with really thin jacketed varmint bullets. I know in past years when the 1-7 twist was new there were issues of many of the really light varmint bullets flying apart but believe most varmint bullets anymore are made with a slightly thicker jacket and I doubt you'd have issues with most of them. But standard 55gr jacketed bullets will be no problem.

Twist rate always interested me and I've done lots of research on it over the years. Green Mountain had a thread on the AR forum a few years back and were doing testing on all sorts of twists like 1-6, and I believe even 1-5 or 1-5.5 twist barrels and from what I remember they shot the light bullets just as well as any other on average.

Here is the breakdown of twist rates for standard 5.56
1-14 will stabilize most 55gr bullets and below unless it is a long 55. But the 55's are on the edge of stability.
1-12 will stabilize most 60-62gr bullets if they are lead bullets and not copper/steel inserts.
1-9 will stabilize most 75-77gr bullets and below if they aren't on the longer side, and should work with all 68-70gr and below unless copper/steel.
1-8 will stabilize everything that will fit in a a mag-length AR magazine
1-7 will stabilize everything that will fit in an AR mag up to rounds that have to be loaded in by hand due to mag-length issues. I'm not sure where the 1-7 peaks out.

For me the 1-8 is the sweet spot for all around AR15 use in 5.56 since the 1-7 doesn't offer an advantage. That said I own more 1-7's then 1-8's since they are more common and I honestly don't think twice about it. It isn't a big deal either way to me because on average they will both shoot about the same.

For you, using longer bullets in the newer wild-cat ish cartridge I would go with the 1-6.5 over the 1-7 or 1-8. From what I remember the 224 valkyrie was having stabilization issues with some of the longer factory rounds when first introduced and they all went with a faster twist which I believe was 1-6.5. So if you want to shoot the heavy bullets in your new 22 Predator I advise getting the 1-6.5 because it should offer no issues with the lighter weights unless you want to shoot really thin jackets. Research the 224 valkyrie I imagine they are both at similar velocities and there should be more info about it out there.