Twist rate and bullet selection

[ronas]

The barrel on my my Colt AR 15 indicates 1/7 HBAR. I understand the HBAR means it has a heavier than standard barrel.

Is their a bullet weight that is stabilized best with this twist rate?

Is 1/9 consider a slower rate than 1/7?

[kermit]

A 1:9 twist rate is fine for military loading in 55-65 gr bullets
A faster 1:7 twist rate will properly stabilize bullets 75 gr or over and shouldn't overstablize the 55-grainers to the point that you would notice.

[ronas]

shouldn't overstablize the 55-grainers to the point that you would notice.

So in other words the 1/7 twist can be used for lighter bullets. Then on the other hand an AR barrel with a 1/9 twist will not shoot as accurately using the heavier bullets.

So a bullet can be overstabilized?

[kato4moto]

Overstabilized is, perhaps, not the correct word here, but I can't think of a good substitute at the moment.

Some 1:9 barrels shoot the 75- and 77-grain bullets very well; some don't. Often, this is due to manufacturing inconsistencies. Some 1:9-marked barrels are actually closer to 1:8.5. Some go the other way.

So, you really have to try as many different weights and types of bullets in YOUR rifle as you can to see what it likes. A 1:9 or 1:8 barrel seems to be pretty versatile.

As for the lighter bullets in 1:7s, there have been some reports of the lighter/thin-jacketed varmint bullets shedding their jackets on occasion in some of the faster twist barrels.

[Jicko]

Personal experience.... both my 1x7 Colt and 1x7 Noveske shoot great from 36gr to 80gr....

36grs are even .22lr!!!!

And with 77gr BHA, both of them are hell accurate.

General belief is that you would *need* a 1x8 or 1x7 if you want to shoot the heavier bullets... 77gr, 80gr etc...

If you have a 1x9, you should try to stay under 69gr or if you are lucky 75gr...

[1911su16b870]

So in other words the 1/7 twist can be used for lighter bullets. Then on the other hand an AR barrel with a 1/9 twist will not shoot as accurately using the heavier bullets.

So a bullet can be overstabilized?

It is actually opposite, 1/7 twist, faster 1 turn in 7-inches is for the heavier (69, 75, 77 etc.) grain bullets, which are heavier because they are longer. Most 1/9 twist barrels will do good with the heavier rounds though, I shoot a dpms 1/9 with a 75 grain Hornady HPBT at 0.5MOA.

[ocabj]

I would not risk getting a 1:9 if you want to shoot 75 or heavier. Just because some people claim their gun shoots 75 in a 1:9, it's not consistent from barrel to barrel. If 75 worked in 1:9, barrel manufacturer would tell you 1:9 will 75s.

Get a 1:8, 1:7.7, 1:7, or 1:6.5 and be happy.

[1911su16b870]

+1 ocabj

Barrel length of 20-inches in my upper. For me the 75s were better than the 69 SMK, 68 heavy match and 77 SMK for that upper.

[Lon Moer]

All ammo questions will be answered by the Ammo Oracle


And "HBAR" is strictly a civilian barrel profile, 'designed' by Colts to cut down on the amount of machine work time.