556 or 223.. whats better for different makers of AR-15's

[ElKellym]

I looked in several other forums here and just couldn't find what I was looking to be answered.

Im just looking for opinions here.

I have a RR ar15 with the bull barrel with a 1/8 twist


Rock River Arms: Varmint Rifle A4


Some people say different AR's shoot 223 or 556 better due to this or that or something else.

A buddy of mine has 50k 556 brass so I would love to use that but how would a amateur like me tell if the gun likes 223 or 556 more shooting?

I do know the 556 has a thicker wall for higher pressures and a little heavier bullet that a 223


I called 2 RR dealerships local here and asked their opinion as well.

1. said t really does not matter since it designed to do both. /facepalm
2. said that it does like the 556 a little better epically on the eject system since its running higher pressure.


Since it is a 1/8 twist am I hampering the stability if I use say a 70+ grain bullet

 

[ksthomas]

No difference at all between the 5.56mm and 223 Rem when you're talking about brass; the difference is in the specs of loaded ammo, and the chamber (mostly throat) configurations of the guns themselves. Running ammo loaded to 5.56mm specs can a problem in rifles using a 223 Rem chamber, but you can go the other way around with no problems. You also have the alternative chamber/throat configurations that somewhat bridge the gap, such as the 223 Wylde, which is what most National Match rifles use today. The 1x8" twist is fine, and will handle anything up to and including the 80-82 grain specialty bullets designed for 600 yard matches. No stability issues here, or with any of the lighter bullets you may want to use.

 

[BC 6.8]

The chamber you have is a Wylde which is designed to shoot either .223 or 5.56 ammo and should give better accuracy than a standard 5.56 chamber. Which brass you use is not that important as long as it is quality stuff. You will need to bump the should back 0.002-0.005" on brass that has been fired in YOUR gun. I know in my gun I have to bump the shoulder back below 1.455" whether the brass was fired in my gun or another gun. You will need a Headspace measuring tool and a set of calipers to do this. I have a 1:8" twist barrel also and can shoot bullets up to 77 gr without issues. I haven't tried any of the 80 gr bullets, but they should work as well with enough velocity.

Hornady Lock-N-Load Headspace Gage 5 Bushing Set Comparator

 

[mtrmn]

556 and 223 brass is identical in external dimensions. Thickness varies between brands and does not depend on whether it's 223 or 556. I've owned probably a dozen or more AR15's and never had even ONE that performed better (from a reloader's/recreational shooter's point of view) with 5.56 pressure levels. Anytime I ever loaded hot enough to call it a 5.56 then accuracy went to crap and I got pressure signs on the brass. I much prefer an average-speed hit over a screaming-fast miss.
We can't tell you what kind of ammo your gun will like because every one is different. You can buy 2 identical guns with consecutive serial numbers and they probably will not shoot the same with the same ammo. I ASSUME you're going to reload since this is in the reloading section. Just work up your loads within 223 specs and I guarantee you will find THE load that works best for your gun within 223 pressure levels. In my book, there's no use for a load going 100,000 fps that throws a buckshot pattern at 100 yds when you can tame it down and get 1/2" groups.
If you're not reloading, then you need to buy several brands/types ammo and see what your gun likes/dislikes through testing. Like others said, with your gun and chamber you can use either but only your gun can tell you what it will perform best with.

 

[Twoboxer]

OP, it is perfectly safe and appropriate for you to use your buddy's brass. The brass itself does NOT make the difference between 223 and 556. For all practical purposes here, it's the same brass. The difference is (essentially) how hot the loads are.

Also as said above, you have a Wylde chamber. This means you can shoot either type factory ammo, and it will likely shoot 556 ammo better than a standard 556 chamber.

I have two RR AR15's, and they are great rifles. Very accurate. Load up following 223 load data, follow safe practices, find the right load for your rifle, then enjoy the reloading and the shooting.

 

[ChemE1975]

as others have said, the brass is the same and your chamber should be okay with either loading. you are going to want to be sure you understand about bump sizing vs. full length re-sizing and likely trimming the cases. then you need to work up a load. if you are up to speed there, great, but if you have any doubts there are great reloading videos on youtube. the series from LonewolfUSMC is great.

 

[BCP]

1. said t really does not matter since it designed to do both. /facepalm

This is true actually. RRiver uses a Wylde chamber which is set up as a hybrid between 223 and 556 and it should accommodate both ammo types.

edit: and yes you will have to full length size and trim...so whatever it was fired in should not matter. I use a small base die on unknown fired brass types just to be on the safe side.