Any info on Velocities on..

[RogerinTPA]

55grain/62 grain out of a 16 inch 1/7 vs a 1/9? How much more velocity will a 55grn bullet out of a 1/7 vs a 1/9 16 inch barrel? Any stats or charts available?

[TWR]

I ran this test with XM193 ammo a year ago, 5 shots averaged. All guns were Colt, the 14.5" was a new barrel with less than 100 rounds fired. Tempature was 86 degrees on 6-25-06, 29% humidity.

14.5" 1/7 twist...3068 fps
16" 1/7 twist...3169 fps
16" 1/9 twist...3147 fps
16" 1/12 twist...3099 fps (old SP1 made in 70's,lots of rounds)
20" 1/7 twist...3275 fps
20" 1/12 twist...3279 fps


Federal GM 69 gr MK same day

16" 1/7 twist...2697fps
20" 1/7 twist...2793fps

[jmart]

Insignificant, there are more variables within the barrel/chamber combos that will affect velocity than the 2" difference in twist rate.

In theory the slower twist should yield higher velocity, but again, many more variables toa ccount for.

[Alpha Sierra]

Insignificant, there are more variables within the barrel/chamber combos that will affect velocity than the 2" difference in twist rate.

In theory the slower twist should yield higher velocity, but again, many more variables toa ccount for.

Agree. This obsession with twist rates is something I have not seen anywhere but in the AR world.

[TWR]

It's hard to determine anything by my test but I agree it's insignificant, the 2 20" barrels were new and show 4 fps difference with a 5" twist difference.

I would think that the faster twist would produce higher velocity because of more pressure but the difference in barrel tolerances makes the most difference.

Twist rate makes a difference in say a 22-250 vs a .223 Rem, while the 22-250 has a slower factory twist of 1/14 and usually won't stabilize anything over 55 grains, the .223 can be had with a 1/7 that will stabilize heavier, longer bullets of much higher BC that will actually make the 223 a better or at least an equal long range performer.

[RogerinTPA]

For those that seem perturbed about this subject in the peanut gallery, I was just curious if a higher velocity would be generated from a faster twist than a slower one, using 55/62 grain for greater fragmentation/bullet brake up. I thought the difference would have been greater using the lighter bullet with the faster twist. I appreciate the info TWR.

[Alpha Sierra]

It's hard to determine anything by my test but I agree it's insignificant, the 2 20" barrels were new and show 4 fps difference with a 5" twist difference.

I would think that the faster twist would produce higher velocity because of more pressure but the difference in barrel tolerances makes the most difference.

Twist rate makes a difference in say a 22-250 vs a .223 Rem, while the 22-250 has a slower factory twist of 1/14 and usually won't stabilize anything over 55 grains, the .223 can be had with a 1/7 that will stabilize heavier, longer bullets of much higher BC that will actually make the 223 a better or at least an equal long range performer.

I fail to see how a faster (within the realm of practicality) twist rate could possibly raise chamber pressure to any appreciable degree.

In order to raise chamber pressure, the barrel with the faster twist would have to offer more resistance to the bullet's fwd motion. I'd like to know how that is possible?

I agree with your last statement in terms of factory rifles, but who here leaves anything as it came from the factory? ;) Buy a Savage bolt gun with a 308-sized bolt face. Buy a barrel vise clamp, barrel nut spanner, and headspace gauges from Midway USA. Buy a pre-chambered 1/8 22-250 Savage barrel from Pac-Nor. Change the barrel in your basement and load up some 22-250 80 gr VLD loads. There is no 223 that can keep up.

[TWR]

rharris, your welcome.

Alpha Sierra, I may not be close but this is how I see it. If a bullet is shoved down a barrel that turns 1 time in 9 inches by the rifling, it's spinning but being forced straight ahead.

Now force that same bullet down a barrel that turns it 1 time each 7 inches and I would think the sharper twist would create more pressure simply because it's being turned sharper. Any and all resistance raises pressure to an extent.

I maybe wrong but it's a moot point anyway. Twist rate didn't show me any signs of greater velocity, of course I'm just a redneck with access to a chronograph, several AR's and the nagging question of "why?"

Edit to add: I have 2 bolt guns a Sako Finnlight in 300 WSM and a Remington LW Mountain rifle in 22-250. When I lose interest in this barrel I'm gonna change it to 22-250AI with a 1/8 twist. That was the original plan until I floated and bedded this "tomato stake".

[Alpha Sierra]

Edit to add: I have 2 bolt guns a Sako Finnlight in 300 WSM and a Remington LW Mountain rifle in 22-250. When I lose interest in this barrel I'm gonna change it to 22-250AI with a 1/8 twist. That was the original plan until I floated and bedded this "tomato stake".
The trouble with the 22-250 and other cartridges that burn a lot of powder relative to their bore diameter is that more of their powder is burned outside the case, scorching throats (flame cutting) in relatively short order.

It depends on what kind of accuracy you expect, but in my Highpower experience a .224" SS button rifled barrel was done around 4000 rounds, sometimes a little less. That is it could not consistently hold x ring accuracy (1 MOA) at 600 yards.

I've learned several tricks to maximize throat life:


Use the slowest burning powder possible as they usually also have the lowest flame temperature
Pick single base powders for the same reason
Keep the throat smooth, using mild polishing compounds like Iosso, JB, or Flitz or better yet, David Tubb's Throat Maintenance System

[TWR]

Thanks for the info, I'll keep it in mind when and if I decide to rebarrel it.

[RogerinTPA]

Found a lot of ballistics data on guns and ammo website.:D