What is the heaviest bullet you would expect a 1 in 9 twist AR to stabilize? I have a new AR with a 1 in 9 and thought I might go fairly heavy. Thanks in advance.

It is not the weight of the bullet but the length of the bullet. Longer bullets need faster twist rates and the shorter bullets don't need as much.

Having said that I have a 358 with 1 in 10 twist that shoots 158 grain pistol bullets to groups that are .33" center to center at 100 yards. That is a lot more twist than that bullet "needs" but I can't argue with success.

Well apparently its 62-70 grains. That weight GENERALLY happens to end up the at the greatest length for that twist. I know its based on the bullet length I wanted to know what weights fell in range for that twist.

Some 9 twist 223 rifles will stabilize 75gr Hornady Amax, but usually around 70gr is the max if the bullet has a boat tail or a VLD design.

You might find these links helpful.

twist rate

AR15 Twist rates

quote:

Originally posted by PaulS:
It is not the weight of the bullet but the length of the bullet. Longer bullets need faster twist rates and the shorter bullets don't need as much.

Having said that I have a 358 with 1 in 10 twist that shoots 158 grain pistol bullets to groups that are .33" center to center at 100 yards. That is a lot more twist than that bullet "needs" but I can't argue with success.

Are those light loads? That's my experience when shooting 110 gr bullets @2,000f/s in .30/06.

Thanks.

sevastopol,

The loads are only light in the bullet weight area. That was with a compressed charge of 48.7 grains of IMR 4064. The standard deviation was 11 and the extreme velocity spread was 32 fps.

I haven't tried any lighter bullets but I have used lighter loads and in the condition my back is in I really like the reduced loads using H4895 and the light bullets. I will be working up a load for the Speer 180 flat point bullet as soon as I get my shop finished and reloading benches built.

Both the 75 Hornady A-Max and 77 Sierra match HP stabilize in the 1-9 twist of my Ruger 77 Hawkeye, shooting at an elevation of about 1,700 feet and MV around 2,800 fps.

Seems 1-9 is on the bubble with these bullets, some do and some don't.

Since you plan to shoot the loads in in AR you might be limited by mag box length more than by twist. Some AR shooters single-load if using cartridges too long to feed from the magazine.

quote:

Originally posted by Magnum Hunter1:
Well apparently its 62-70 grains. That weight GENERALLY happens to end up the at the greatest length for that twist. I know its based on the bullet length I wanted to know what weights fell in range for that twist.

The maximum 223 bullet length that a 1:9" barrel twist should stablilize is right at about:

1.00" if you can keep the MV over 2,800 fps.

Having said that, there probably a "grey area" of about +/- 0.06" arround this 1.00" bullet length where your particular rifle and your particular that is in question.

I.e. Below 0.94" your probably OK and above 1.06" your probably not. If you pick a bullet inside this grey area you should test'em for stability out to the longest distance you plan to shoot.

Throwing a fly in the ointment....hollow pointing changes things for the twist.

Don't get technical, load up a few and try them..sometimes all the accepted facts of twist and bullet weight go out the window and what is not supposed to work works better than anything else....I have seen this happen many many times.

If your building or buying a rifle its very important to purchase the proper twist for desired bullets,but if you already have one by all means follow the above and give them a try.

quote:

Originally posted by Atkinson:
Don't get technical, load up a few and try them..sometimes all the accepted facts of twist and bullet weight go out the window and what is not supposed to work works better than anything else....I have seen this happen many many times.

If your building or buying a rifle its very important to purchase the proper twist for desired bullets,but if you already have one by all means follow the above and give them a try.

+1.

"In theory, theory and practice are the same. In practice, they are not." — former New York Yankee catcher Yogi Berra.

I'm in the process of building a 22-250 with a 1-8 twist to shoot the 70 to 80 grain VLD type bullets. I've done it before and the accuracy out to 800 to 1000 yds. is amazing. You will probably go unstable at around 70 gr. with a 1-9 twist.......Tom

Like Ray stated- test.

Out of a bolt gun, with a fairly long bbl, MV is the driver. (spin = twist rate x velocity), in other words, a too long bullet in a 20 inch AR (low velocity) may certainly be stable in a longer bbl (higher velocity) situation.

Also, measure your twist to see if indeed it is as specified, often they are not....

There are several useful stability calculators on the web.