Best AR/twist rate for factory 55gr/62 grain?

I recently got into competition shooting at my local range, beginners were firing out to 100 yards while the more advanced shot at 300 yards. Rifles being used were M16-style rifles (used one on loan from the club for the competition), and I actually rather liked the 20 inch AR platform. Talking with some of the more seasoned shooters I quickly found out all the little intricacies of their rifle/ammo. I don't really have the cash/knowledge to get a high-end AR and make custom reloads, so here's my question.

What twist rate works best for a 20" inch AR with common factory-made 55 grain and/or 62 grain ammo?

What company makes a good rifle for that specific platform?

Maybe later on down the line, I can experiment with premium ammo/rifles. Until then, just looking for something stock/basic that can give very good accuracy.

Thanks-

Rules of thumb:

For 55gr, 1/12 was the "standard" for years before the advent of 62gr bullets. 1/12 stabilizes 55gr just fine.

For the 55gr and 62gr combination f yours, 1/9 is optimum.

For anything > 62 gr and up to ~ 78gr, the 1/9 and 1/8 twist rates seems to work well.

From 78gr to 90gr, the 1/7 is needed.

That said, my ARs have either 1/9 or 1/7 and stabilize 55gr just fine, with no evidence of overstabilization or disintegration.

Also, don't go by weight, go by length. Weight increases with bullet length, but stabilization is a function of length. Those hollow pointed target BTHP bullets are the tricky ones; long for their weight, requiring a faster twist.

HTH,

Noah

There are numerous graphs/images that are ok as a reference. Everything comes with a caveat "generally speaking"

10 years ago it seems like most AR's were 1-9 maybe 1-8, with 1-7 being hard to find. Now, I'd dare you to try and find a factory built rifle with a 1-9 twist. Most everything has gone 1-7 which I think is ridiculous. It will be a long long time before the standard 55 or 62gn bullet isn't standard anymore. So, when I shop, I shop for 1-8 with a second of 1-9. I might have bought a Tavor if they weren't all 1-7 but that's just me. Sorry, enough of my ranting :D


https://www.pewpewtactical.com/wp-co...Twist-Rate.jpg



https://www.glocktalk.com/cdn-cgi/im...rt-jpg.453950/

You have to experiment with the ammo. My current 16" barrel 1:9 shoots the 55 and 62 very nicely. The 55 has a slightly better grouping at 100-300yds. I did have a Colt Sporter 20" heavy barrel with a 1:7 that would only shoot 62gr and above accurately. The 55gr was atrocious in that rifle. 1:7 was specifically designed to shoot the 62gr projectile out of a 20" barrel. I reloaded the 62gr green tip and Winchester 62gr soft points for that rifle and it was very accurate but the best round I shot out of the rifle was a Federal Premium 69gr FMJ Boat tail hollow point. I don't even know if that's still manufactured.

Don't forget there are other factors that influence ammo accuracy besides length and weight of projectile. There's concentricity, powder charge consistency, etc.

Good match grade ammo/rifles may be agnostic to bullet weight. Just depends and you'll have to test.

If it's a combination of .223 and 5.56, you will want a .223 Wylde barrel in 1:8.

I had always though 14.5" 1:7 was designed to shoot 62gr green tip, and the 1:9s were more accurate with the 55gr., but ExFlyinguy's 2nd graphic makes it look like both weights are in the sweet spot for all three twists. His first graphic makes it look like all you ever need is 1:9 twist, but wonder how barrel length impacts this. Is 1:12 twist standard for 20" barrels or was that just in the original M16s?