20" .223 AR-15 max bullet weight 1:9

[freebound]

Good morning... long-time reader, first time poster...

I have a Rock River Standard A4 with a 20" HBAR barrel, 1:9 twist.

I've read many times here and elsewhere that the max bullet weight a 1:9 barrel handles well is 69 grains, anything heavier needs a 1:7 twist...

But I've also noticed that the vast majority of this discussion assumed a 16" barrel... there's just not many people talking about performance of 20" barrels. And I've noticed that there is a 24" barrel sold with a 1:12 twist. If that is the case, it seems that a longer barrel needs less twist to stabilize a bullet (or why would Rock River sell a useless gun?).

From that, can I deduce that a 20" 1:9 barrel should be able to handle 75 grain bullets? 77 grain? I'm guessing I'm right on the edge, and I'll have to test it myself in some long range shooting to find out. But does anyone else have actual experience? Thanks!

[ScottRiqui]

Barrel length has very little (almost nothing, really) to do with the twist rate necessary to stabilize a particular length of bullet. The 24" barrel you saw was probably a dedicated "varminting" rifle, designed to shoot shorter bullets at great speed.

You're correct that ~70 gr is about the limit for a 1:9 barrel. I don't think you're going to have much luck with the longer 75 gr or 77 gr bullets, regardless of barrel length.

[Bartholomew Roberts]

Some 16" 1:9 barrels will do fine with the 75gr. Some won't. I would guess that the 20" may give you a slight edge; but will probably show the same characteristics (some will, some won't).