Heavy 223 Bullets in 20" Barrel

I would assume twist is twist. I suspect it’s more to do with individual barrels

It is all about the twist for bullet weight. Length of barrel plays with barrel harmonics. If you reload then the harmonics are just a matter of finding the sweet spot.. Quality of barrel plays with everything.With mine, the rifle and scope and with the right load will put 5 at 100 yds that can be covered with a nickle. Me, I got to have a good day to hold up to what the rifle can do.

I have had excellent results with 77 and 75 grain 223 from 1:7, 1:8, and 1:9, from 10", 11.5", 14.5", 16", 18", 20".

It's an individual barrel thing.

My 1:7 does OK with 55s (Nosler BTs for coyotes), but it really shoots well with the 60BTs, 69 and 77 OTMs. IF you're shooting regular FMJ that's probably your issue. I've only managed to get a couple FMJ loads close to 1MOA. They're usually 1.5 -2MOA even with load development

For "all around" I like a 1:8" easier on the light bullets and does well with the heavies.

DMW1116 said:

Maybe I asked the question backwards. Will the longer barrel suffer accuracy loss with the lighter bullets, or will the faster twist cause accuracy loss with the lighter bullets and higher velocity?

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It's a barrel twist thing. My 1:7 20" Colt H-bar pretty much hates everything 55grn, but works well with 62's and 69's. My 1:8 16" RRA doesn't seem to care either way. Barrel length, particularly a heavy barrel, should contribute to accuracy, not detract from it... but as Chuck says, it's up to the individual barrel.

Better bullets might help... the mass produced 55grn FMJ is not designed for accuracy work... but the real solution is a heaver bullet. I've gone to 62grn BTHP's (and FMJ's if I could find them) for reloading now... at least for my Colt. Match bullets are expensive... too expensive for blasting ammo, for sure. I have a stash of 69grn SMK's, but I don't shoot those very much.

Army uses 1:7 in their DMRs.

DMW1116 said:

Maybe I asked the question backwards. Will the longer barrel suffer accuracy loss with the lighter bullets, or will the faster twist cause accuracy loss with the lighter bullets and higher velocity?

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Generally the longer barrel will give higher velocities especially with slower burn rate powders, the longer length will likely allow a greater effective range.

A 7 twist should handle anything up through 85 grain boattail spitzers according to Berger. But if you want to load from the magazine, the 77s are the heaviest I know made for rapid fire.

DMW1116 said:

Aren't those intended to shoot the heavier Mk262 rounds? I guess the 55s or 62s will work in a pinch.

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With a 1:7 I shoot 62s when using FMJ. The 62Grn Hornady's are the best I've found, luckily I'm sitting on a couple 1000of them. My load hovers just over 1MOA for 5 shots. Some guys report excellent accuracy with FMJ, but I'm not one of them. I tried my best load in my 18" barreled SPR with a WOA match barrel with matched bolt, easily a 1/2 to 3/4 MOA gun, and still hovered around 1 MOA.

For heavy "match" bullets I use 69 OTM for a 1:9 (also the 69 grn Sierra Tipped MK) and 77s (MK262 clone load) in 1:7 and 1:8. The Nosler 60BTs are long enough to shoot pretty well in a 1:7 and still get decent velocity for rapid expansion even in my 16" barreled guns. That was my "go to" coyote load for my Colt with 1:7. Now I'm using a 1:8 homebuilt gun and back to 55s.

As Jim Watson said, the 77s work well in mag length, they were designed to. Other heavy bullets may or may not, and you might have to single load. I've still got a bunch of 75 Hornady's that I bought by mistake that will not work in an AR at mag length.

DMW1116 said:

Which 75 gr Hornadys won't work? That what I use in my 16" barreled rifle. The one I have feed from the magazine. They have a couple that won't though I think.

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Older 75 Grn AMAX, but from what I've read the ELDs are in the same boat. I was trying to replicate the 75 grain TAP load....but ordered the wrong bullets. IF I load them single style I can shoot them and they're accurate.

DMW1116 said:

The higher velocity is part of the reason for the longer barrel. I already have a stock of 55gr FMJ projectiles for hand loading. I'll dig around and see what else I can find.

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The 55 fmjs make for good range blasting ammo, and we do have fun with them; when we need good accuracy (minute of prairie dog at 400 yds type of accuracy), use better bullets. Plenty of 55 gr bullets will shoot well.
https://www.midwayusa.com/product/101093139?pid=280317

I use nothing but 75gr bullets on my RRA predator with a 20" barrel. Shoots better than the guaranteed 3/4 moa from RRA and even better with handholds. My barrel has a 1:8 rifle twist.

DMW1116 said:

The higher velocity is part of the reason for the longer barrel. I already have a stock of 55gr FMJ projectiles for hand loading. I'll dig around and see what else I can find.

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Even a cheap 55 flat base is better than a fmj.
If you're shooting clay pigeons, pop cans, or steel plates. The fmjs will work. If you're going for the best accuracy you can find. You need to look for a better bullet.

My AR with a 20" 1/7" barrel LOVES 75&77gr bthp bullets. Under 1moa we the reloads, right at 1moa with factory 75's &77's. Less than 3moa should be no problem. The longer barrel may actually do better with heavies because of the extra velocity.