mlaubner

OK, here is the quandry. I currently own an AR-15 clone with a 1:9 twist. I have ammo that shoots well from the gun and it is very accurate.
I want a .223 bbl for my T/C Encore, however the factory twist rate in their bbl is 1:12.
I can get the .223 bbl in any length I choose, but with that twist rate what is the best length bbl for this caliber with this twist rate.
Please feel free to make bullet weight suggestions with your answer.

To me this is just very perplexing because a 14.5 in bbl in my AR will easily group 5 shots in under 3/4 inch with a 1:9 twist shooting 55-62gr bullets, however the T/C bbl guarentees that their bbls will shoot M.O.A. also. Now they don't specify what length of bbl what weight bullet, it is just a blanket guarentee<probably done more for marketing>but I have found it to be true with the other bbls that I own.
Thanks to all.

Briman

Don't know the facts for sure, but I overheard a good highpowershooter talking about his AR barrel at a match. He had a barrel with a 1:7.7 twist rate and said that it was necessary in the AR for heavier bullets because the velocities are lower and the barrel is shorter than on a bolt action varmint rifle where a slower tiwst rate will work just as well.

mlaubner

Nothing quite like a custom made Kreiger bbl.
But I have a wife and five boys to support so that is not an option on my AR.[]
Most of the "varmit" bbls I have seen on AR's are in the 20-24 in variety, again with a 1:9 or 1:8 twist.
So if it was your money/gun, what length of bbl do you request?
I can have any length I want, from 16"- 26", but if 20" works well in a 1:9 twist then should I get a full length bbl (26") with a 1:12 twist? or will 22 or 24 inches be just as accurate?
At what point (length of bbl) will velocity start to suffer or errode? Can the bbl be too long?

icthruu

The faster twist is meant for heavier bullets. Heavier bullets=slower velocity, and thus require faster twist to stabilize them. With the lighter(faster) varmit bullets that fast a twist rate can literally cause the bullet to come apart. The 1 in 9" twist is a compromise, military rifles use 1 in 7" twist for standard 62gran ammo. Most bolt guns in .223 will have 1 in 12" twist, and I have seen one in 1 in 14" twist.

There is a point at which increasing barrell lenght won't provide any increase in velocity. From what I have seen, 22" is a pretty standard length barrell for .223rem in 1 in 12" twist.

Good luck

mlaubner

Thanks icthruu, but do you have any information on bbl lengths greater than 22"?
Is there any negative effects on the flight of the bullet with a longer bbl or am I just toting around more steel pipe than I need to? This will definitely be a ground hog rig and not meant for stalking around the woods, so the weight is not a real issue, I just want the most accuracy and velocity I can wring out of the bbl and know that length and twist rate need to be optimal.

bigbulls

Barrel length has absolutely nothing to do with calculating the twist rate needed for any given bullet other than adding or subtracting velocity.

What you need to do is refer to some reloading manuals and other charts to figure out how fast a given length bullet will travel with a given barrel length. A bullets velocity will change about 30 fps per inch of berrel added or removed when the bullet is traveling between 3000 and 3500 fps. So from a reloading manual you can get pretty close in figuring how fast a given bullet will travel with a given barrel length.

Measure how long the bullets are that you might be using and go to the calculator at the link and you can figure out how the minimum velocity for each given bullet. Then take this information and refer to your reloading manuals to figure out how long of a barrel you would need to achieve a certain velocity.

EXAMPLE: The barrel is 1 in 12 inch twist rate. The bullet is .723 inches long and the bore is .224 inches. Plug in those numbers and you get a minimum velocity of 2441 fps. to stabilize that particular bullet. You can get that much velocity out of a revolver.

A 1 in 12 twist barrel will stabilize bullets up to about .8 inches long at 3000 fps. and that is a heck of a long .224 bullet.

http://www.uslink.net/~tom1/twistrate.htm

mlaubner

Thanks bigbulls,
Thast is exactally the information that I was looking for!
Mark