1/5 Twist and Supers

[pj-schmidt]

8" 1/5 twist, Nosler 110 Varmageddon, 2150 fps. Roughly 310,000 rpm on the bullet.

Hot barrel, near the end of the first magazine on a walk through carbine course. My wife was shooting and I could see rounds basically flying everywhere, By the time I got her stopped the can was toast.

...

When I called Nosler, they would not give me an upper limit for RPM. I then explained the above and the answers was "that's probably too fast, too hot or both.

Given this example, I'd have to say I have underestimated the risk.

Personally I'd never buy a 1:5 twist barrel since I've had very good success with subs in 1:7 and 1:8 barrels.

[offsidewing]

Anecdotal evidence, but my 7 inch Q barrel groups 125gr TNTs loaded with N110 for accuracy as good as my 9 and 10.5 inch, 1/7 barrels out to 200 yards. The Q barrel groups long, heavy subs slightly better than the other barrels. I've shot three different Q barrels with similar results.

That being said, if I want to chase velocity at distance, it isn't going to be out of a 7 inch barrel of any twist rate.

[dellet]

8” 1/5 , field bipod off the bench, unsupported rear, 6X Trijicon, 150 grain Gold Dot, 1950 fps, Two sighters and a shot for score at 100 yards.



Barrel length and twist arguments are mostly garbage until you want to drop below 1/2 MOA. Knowing bullet limitations is a different story, but with a cartridge like 300 Blackout you need to know those limits.

[bearcatrp]

Dellet, would you recommend 1:5 twist for 30”BO? Looking at your target, looks like it would be optimum. Did you have to order special to get the 1:5 twist? Have never seen that sold.

[dellet]

Dellet, would you recommend 1:5 twist for 30”BO? Looking at your target, looks like it would be optimum. Did you have to order special to get the 1:5 twist? Have never seen that sold.

I chose 1/5 for a rifle that I shoot mostly subs, knowing there would be some limitations on supers. It’s tough on bullets and over 8” 300,000 rpms are common. There are plenty of bullets that will hold up to that, but not a lot that will expand at Blackout velocities. It’s just a choice. The flip side of that is that the centrifugal force that causes supers to come apart in flight, helps both the supers and subs to come apart in tissue.

People think you give up a lot in precision in a short barrel. All you really give up is velocity and that’s more to the point.

Here’s the same bullet at 2100 fps from a 12” 1/10



I can show similar results with any barrel I have. One of my best groups with factory ammo, Remington 120 UMC, was about 5/8” at 200 yards with a 24” 1/6. Then there were multiple 2 1/2” groups at 200 with a 24” 1/10 shooting subs with 220 grain bullets that were barely stable. Those results fly in the face of common thinking about the cartridge.

I really don’t care what the barrel length or twist is and would recommend anything between 1/5 and 1/11 depending on use. Just realize something optimum for subs, may not be optimum for supers, or the reverse. Any thing you want to shoot bullets from .850”-1.850” at speeds from 1-3000 fps will require compromise. Just keep that in mind when you plan a rifle and choose a twist that will compliment your goal, or play it safe with a middle of the road compromise.

Barrels I have used to base this on.

6” 1/7
7” 1/6, 1/7
7.5” 1/5
8” 1/5, 1/7 1/8
9” 1/7, 1/8
10” 1/7
12” 1/5, 1/10, 1/11
16” 1/7, 1/8, 1/9
18” 1/9, 1/10
24” 1/6, 1/0

[bearcatrp]

Thanks for the information. Food for thought.