I have a 10.3" LMT that is suposed to be kind of my "go to" rifle. When i got it i lived in Atlanta and 10.3 was perfect but I am rethinking going 11.5 or 12.5 now that I live in a more rural area.

Some back ground, i have another 10.5" SBR that is loosely a MK18 Mod 0 that I intend to serve as a "bedside gun" inside the house or vehicles.  
Here is how this one looks. It usually wears a MG7 or Turbo K suppressor and still needs a light.


Those factors have made me consider changing my LMT to a 11.5 or 12.5". I would also like to change the handguard to something different. Nothing at all wrong with the BCM. I actually really like it. Just considering other options. I want a HG lighter than the 14.5oz DD RIS II and dont need the quad rail otherwise it would be the obvious choice. It would like it to still be strong enough for IR aiming devices and "hard use", not that I am in a war zone or anything. Considering the Centurion CMR which i have and like on another rifle, Geissele MK8 or maybe a DD MFR but open to other ideas. Also, if i swapped barrels what barrels do you recommend? Leaning toward something Like a Criterion CORE, DD or other "good quality" chrome lined barrel. But i have also had very good luck with Rainer match barrels if i wanted to go stainless.
Here is how it currently sits. Nothing at all wrong with it. Just perpetually thinking about if something else would be "better".

I am fully in the 12.5" camp. My Geissele 12.5" shot tighter when zeroing than my 12.5" Criterion Core did, but the testing stopped there. They are both really nice barrels. I've got a PLXc 1-8 on the way to try on this build.

ETA: This helped me decide - https://www.ar15.com/forums/ar-15/Suppressed-5-56-SBR-Velocity-Tests-41-Factory-Loads-from-10-5-11-5-12-5-and-14-5-ALL-DONE-/16-714088/

I'm in the 12.5" carbine gas camp. I could not get an 11.5" carbine gas to run consistently or well below -10° F even drilling out the gas port to .125", but that was unsuppressed.

12.5" carbine suppressed always runs, so far.

ETA: Duck autocorrect

My son just built a 12.5" pistol. I'm jealous of it.

I’d say 12.5. I have both an 11.5 and a 12.5, and if you already have a 10.5, may as well do 12.5.

I really like the 12.5 and it is much better with the can on it. Less muzzle flash and more velocity.

12.5 master race

I always answer 12.5” to this question. It’s easier on the can than shorter barrels, less flash, more velocity, just right handguard lengths, not unwieldy unless your technique is poor, etc.

12.5" is the best "do-most" length, IMO. There isn't that big of a velocity jump going from 10.3" to 11.5", but there's a pretty large one going up to 12.5".

In fact, with 55-62gr ammo, you'll get velocities in par with a 14.5". And speaking of which, if you live in a more rural area now, have you considered going 14.5"? You will get better ballistics with 75-77gr ammo over a 12.5" and you can typically avoid an SBR stamp when pin and welding most suppressor mounts. Or just run a brace, I guess.

And on a side note, you should really get a weapon light.

What handguard is on that AR?

I have a 14.5 P&W sent out to D Wilson as we speak. Dont need it at all. But i sold a PSA 16" upper that i never used. Picked up a used 14.5 upper. DD upper, DD rail, DD chrome BCG and CORE 14.5 barrel. Felt like it might be a little upgrade from the PSA 16".

Disclaimer, the PSA was actually pretty good. It was one of the CHF barrels made by FN. Shot about 1.5 MOA or better first trip out with 77gr OTM.

It's a Forward Controls Design RHF. It's their 11.5" version with a 12.5" Criterion Core.

They make one in 13.7", which with your 14.5" Core I bet would have bare minimum gap between the handguard and your can, if that matters to you.

Here's how close it is on my 12.5" Core / 11.5" RHF

Thanks. The 14.5 has a DD MFR on it. I haven't used it much but like the feal of it and it is reasonable light weight. Probably wont change that since the rifle is going to P&W.

Can you tell me what type of accuracy you are getting out of the 12.5 CORE?

I've had this thing built for a couple years now and still have never sat down at a bench to really test the accuracy of this thing. I'm always just blasting steel at my clubs action ranges with it.

Thanks any way. I am always thinking about 3 builds ahead of what I am working on. Probably wont get this one done for a long time. But I think I am sold on the 12.5.