My 10.5” (1/7 twist) has a red dot sighted in @ 25 yards.

What size group can be expected at 100 yards with a magnified optic, with everything else working as it should?

Will using a premium 223 75 gr BTHP help close the gap or does the 10.5” negate that?

PSA 10.5 sub MOA at 100 with a good rest.   1-4x Bushnell

1/7 and short barrels are both supposed to prefer heavy projectiles, so you are on the right track there. Barrel length should only affect velocity and not accuracy. Will depend on how decent your barrel is. Try it and post back.

Unless your barrel is total crap, you should be able to print MOA or damn close with quality ammo.

Thanks for the info.  I had no idea a 10.5” was capable of sub MOA at 100 yards.

My 7.5” is an econo build, but I did use quality parts in my 10.5”.  However, I can’t remember where I got the barrel.  If I can’t get close to 1”, I’ll change the barrel out.

I have a Trijicon 1-4 to put on it and a LaRue trigger that should get me there.

I’ll post results when AZ temps are below 100… and this post will be archived.

my 10.3 LMT MK18 with KAC front end, TA01 4x32 ACOG, shooting Australian Outback 69 Sierra Match kings...LaRue MBT, indoor, 100yd off a bag, 5 shots...groups were under 1.5, but not under 1.0

Your results will vary based on a lot of factors, but a 10" barrel isn't one of them. Assuming it's a decent barrel, I'm willing to bet the results will surprise you.

On a lark I took a red dot 10.5" to 600 yards on a bullseye target running MK262 77's.  After dialing in, it was grouping x's and 10's on an NRA regulation target.    Pit guy didn't know, and was wondering why the impacts sounded so weak.  

Your gun will shoot just fine at 100 yards, even with a red dot.

Some obvious trick of course:
- turn down the dot power so only a little visible. For a more precise dot.
-50 yard zero IMHO is a more practical general purpose zero than 25.  And will only be about 2" high at 100.  A 25 yard zero will likely be off the paper at 100.  (Unless big paper).  It's overbore offset is 2-3" high, bit a 25 yard zero is only useful at 25 yards - its not any better at 10 yards than a 50.
- 50 yard zero is close to a 200 yard zero - even with a 10.5, and will be able to nail 200 yard steel gongs all day dead on.  And 100 yard steel gong if you aim at thr bottom.
-wear ear protection. Wear good ear protection.
- a BCM mod 0 warfighter muzzle break is AWESOME!  Same size as the A2 and designed to minimize operator concussion from a brake.   2' fireball and a concussion to everywhere else but you, will dominate the range  
(Most any setting other than a nighttime jungle ambush from hidden locations, and that shit is a feature baby! not a detriment!)

Thank you for your response and info.

Barrel length only affects velocity, not accuracy.

Not sure I agree that any decent barrel should be able to average 1 MOA.  I have a couple of AR's that are capable of this kind of accuracy - a CLE and a LaRue, but those are my two most accurate AR's.  Best I can do with my DD's and BCM's is around 1.5-.6.  But maybe that's just because I suck.

Of course, unless you only have 1 AR, not sure why you'd want to try to shoot a 10.5" AR out to 600+ yards, except for fun and the challenge.  At those distances your bullet is going to start dropping like a stone, it will be tough to shoot if there's any wind, and you won't impact your target with any real velocity.

To me, a 10.5 or 11.5 inch gun is made for a red dot, maybe a suppressor and to be shot offhand at targets 100 yards and in.  You want to shoot out to 600 with any frequency get a gun with an 18-20" barrel a bipod and a decent magnified optic.

I just sighted in a new pistol yesterday and was surprised by the good accuracy. Radical Firearms 10.5" 1:7 Wylde chamber 5.56/.223. Shooting PPU 69 gr BTHP match. Sight is a Sig Sauer Romeo5 red-dot. I had roughed it in with a chamber laser before going to the range so it was on the paper. I moved it to the center, 1.5" low. This is pretty much the '50/200' zero. I was getting 1.5" groups which is about it for me, which translates to 4 MOA or 8" at 200 which is close enough for a pistol. Magnified optic or not, if you can't shoot you're not getting 1 MOA at 100. If you can shoot, you'll get that with irons or a dot sight. I sold my ACOG 4X because of weight and the fact that I just like the reflex dot sight better.

Good optic and good shooter are the limitations, barrel length is not. Barrel length impacts velocity, not accuracy.

Have you ever shot 1" at 100 yards with any AR15? If not, why would you consider changing out a barrel?

The AR is a 4moa gun as standard. That's still 'minute of bad guy'.

I'd be very happy with a 2MOA 10.3-10.5" gun - mine is ~2MOA with a DSA barrel and has done phenomenal out to 200yds.

1MOA? I mean, less MOA = moa better, but... not critical IMO.

Not sure what this means.  You mean bulk AR ammo is 4 moa ammo?!?  No gun is a 4 moa gun "as standard", but if you shoot 4 moa ammo through any gun to expect more than that would be "optimistic".