1x7 or 1x9 twist rate ...QUESTION

[baffle Stack]

This is a contradiction. When a projectile looses velocity and become unstable it most assuredly looses accuracy. The length of the barrel does in fact effect how fast the bullet spins.

Not if you measure as Hawkeye did, Revolution per distance traveled. (Rev/unit length. In this case 9 or 7 inches) With this unit of measurement Revolution would not be dependent on barrel length. However if you measure revolutions per unit time (Rev/unit time) Then you are technically correct because longer barrel = more velocity (distance traveled / change in time) and in turn that = faster revolution because it is traveling the same unit of length only quicker. It gets confusing because we’re talking of both revs/length and revs/time

Again, this is not correct. The bullet may spin one complete revolution in 9 inches but in the 20" barrel the projectile is in fact spinning faster because it is traveling faster. For instance, if you fired a 77gr bullet out of a 10" 1/7 barrel it would still be spinning slower than a 77gr bullet fired from a 20" 1/9 barrel. If you look at the majority of the bolt action .223 rifles you will see most are 1/9 and slower but still fully capable of stabilizing 77gr and heavier projectiles.

Technically yes. Again just look at Hawkeye's unit of measurement and you will see he is not incorrect at all. He is using the unit of measure that all our barrels stamped with. Rev/length. i.e. 1/7, 1,9, which has nothing to do with time.

[K.L. Davis]

Highpower shooters using ARs have pretty much settled on 1/8 as the standard since at least four or five years ago.

It will shoot everything from 45 to 80 grains with sub MOA (often in the fives) accuacy. More than good enough for any use short of benchrest competition.

About 5 years ago, I had some barrels made up: Stainless, Wylde Chamber, 1:8, 16" mid-length gas system -- I tried to sell them

At the time, all of the *experts* found elsewhere where like...

"One in eight? what is that? And no one would want a stainless barrel, IT IT'S NOT CHROME, GO HOME!... that mid-length thing is a fad... what a waste of money"

I have been shooting 1:8 for a long time...

[K.L. Davis]

... some stuff was here ...

Not sure what you are asking... figuring rate of twist for stability is determined by actual RPM of the round more than anything.

In order to get this, we get the velocity over a reasonable distance and just assume that it is constant (of course it is not, but you will see how it works).

So, say we have a velocity of 2700FPS, and a ROT of 1:7

We want to make everything feet, so divide 7 by 12 and the ROT is one revolution every 0.583 feet.

The round travels 2700 feet in a second, so by dividing 2700 by 0.583, we can see how many times it will spin in one second... 4631 RPS

Then we multiply that by 60 to get the revolutions per minute... 277,873 RPM

[Alpha Sierra]

About 5 years ago, I had some barrels made up: Stainless, Wylde Chamber, 1:8, 16" mid-length gas system -- I tried to sell them

At the time, all of the *experts* found elsewhere where like...

"One in eight? what is that? And no one would want a stainless barrel, IT IT'S NOT CHROME, GO HOME!... that mid-length thing is a fad... what a waste of money"

I have been shooting 1:8 for a long time...

Ain't it sad what the herd mentality and lack of critical thinking does?

[Milkman]

Not if you measure as Hawkeye did, Revolution per distance traveled. (Rev/unit length. In this case 9 or 7 inches) With this unit of measurement Revolution would not be dependent on barrel length. However if you measure revolutions per unit time (Rev/unit time) Then you are technically correct because longer barrel = more velocity (distance traveled / change in time) and in turn that = faster revolution because it is traveling the same unit of length only quicker. It gets confusing because we’re talking of both revs/length and revs/time



Technically yes. Again just look at Hawkeye's unit of measurement and you will see he is not incorrect at all. Now can someone find the relation between revs/length and revs/time? That would be interesting. I have an idea but I don't want to bore you guys nor hijack the tread

I read exactly what was typed and answered accordingly. A projectile leaving a 10" 1/9 barrel is not turning at the same rate as a projectile leaving a 20" 1/9 barrel. Barrel length does have any effect on accuracy and is a condition for reaching stabilization of a projectile. No where was "revolution per distance" mentioned, only "rate."

[baffle Stack]

I read exactly what was typed and answered accordingly. A projectile leaving a 10" 1/9 barrel is not turning at the same rate as a projectile leaving a 20" 1/9 barrel. Barrel length does have any effect on accuracy and is a condition for reaching stabilization of a projectile. No where was "revolution per distance" mentioned, only "rate."

Would not "revs/distance" be a measure of rate? Meaning 1 rev per unit length measured. That seems like a rate of twist to me. Its just a funny one because it is not relative to time like we're are all used to.

I'd be happy to discuses this further Milkman, but lets do it via IM as not to spam Hammerdrop's thread.

[baffle Stack]

Not sure what you are asking... figuring rate of twist for stability is determined by actual RPM of the round more than anything.

In order to get this, we get the velocity over a reasonable distance and just assume that it is constant (of course it is not, but you will see how it works).

So, say we have a velocity of 2700FPS, and a ROT of 1:7

We want to make everything feet, so divide 7 by 12 and the ROT is one revolution every 0.583 feet.

The round travels 2700 feet in a second, so by dividing 2700 by 0.583, we can see how many times it will spin in one second... 4631 RPS

Then we multiply that by 60 to get the revolutions per minute... 277,873 RPM

Don't worry about it. I think I errored in my quoted text. But thanks for the info still.

[T-700wrench]

First Post
Nice forum
The only time I have had trouble with a 1/7 twist with any bullet was with a Pacnor 22-250. The 50 gr Vmax would blow up at around 3900. They were still incredibly accurate, except for the ones that made a puff of smoke about 50 yards downrange. I shoot them all the time in 20'' A2 barrels. They will blow up in a coyote and not leave an exit wound at as close as 60' or as far as 310 yards at a mv of 3300. The 80 grain sierra will blow in a 1/7 at 3850. This I learned from a 22/6mm Ackely.

[royta]

OK, so 55 FMJ in 1/7 is just fine. However, I didn't read anything about 55 Soft Point or Ballistic Tip. I'm guessing the standard jacket Soft Points will be just fine and very accurate, but I'm not sure what would happen to the thinner jacketed bullets like a V-Max. Anybody out there with experience with 1/7 16" barrels and 55 grain hunting/varminter bullets?


T-700wrench - I also have a Pac-Nor .22-250. It's a 1/12 though. Super Match Stainless Steel, 3-groove, 24", #5 Sporter contour. Awesome!