So I had an interesting although not scientific observation. I’ve been developing a load and trying factory ammo in a LaRue stealth barrel with a bare muzzle. I was getting full choke patterns with most everything.

My intent was to do the load development clean and come back with a MB/suppressor and make sure it wasn't the stuff hanging off the end of the barrel.

With the same gmm ammo, the groups tightened up from 2” to sub MOA at 100 just by adding a brake.

I want to know if others have seen this and also wonder if we’d be better off getting 5/8 or the largest threads possible on heavy barrels to minimize whatever might be going on in the last 3/4” of Barrel.  Perhaps just a thread protector might help?

Any thoughts?

Torque from the muzzle device can have an effect, positive or negative on group sizes.

Most competition AR-15 service rifles have flash hiders timed to be tightened by hand tension alone and Loctite.

You will probably be better served developing your loads with the can installed if that's how you intend to run the rifle.

I can't get FMJ bullets to shoot worth a damn and refuse to buy them. The only brand that can be recommended is Hornady's, purchased in 6000 bullet boxes they're a steal.

My standard AR load is 24.5 grains of Varget with Sierra 69 grain Match King's seated at 2.250". This load has proven itself through dozens of rifles, both mine and my friends.

52/53 grain match bullets from any of the big three manufacturers will hammer tidey little groups at 100 from every twist barrel. 1/7's will shoot them lights out.

Try better bullets if you want better results.

Why develop a load for bare muzzle if you're going to use a MD?

It can affect harmonics.

It's been my experience that the heavier muzzle devices (such as QD suppressor mounts) will generally improve groups; sometimes pretty dramatically.

In terms of doing load dev, it's better to develop a load with a bare muzzle then screw something on that it is to do the opposite.

That said, I'd be doing load development in the configuration you plan to shoot the rifle.

Edit: I just went through this recently, where I developed a load for F-Class with a flash hider on the rifle. It was shooting ~.3-.5 pretty consistently. When I put a suppressor on it, it got even tighter (some groups literally looked like a single hole).

I ended up pulling the flash hider to be more F-Class compliant, and the groups opened up to .7-.9 with the exact same load. Had to adjust seating depth to get them back in the same territory as the bare flash hider.

I watched a video that showed pretty clearly that the thinner the resulting barrel, the more opened up the muzzle gets. It had a guy testing with pin gauges and was pretty severe and clearly attributed to the threading.

https://youtu.be/CUm_YXzJJOU

Anyways. I’m still waiting on a tbac can. My m4-2000 is a ratchet mount which is known to be questionable as far as load development since they all have a little wobble.

Improvements from the brake are likely due to two things:
1) Reducing recoil. Minimal with a 223, but gas guns require proper form. Any reduction in movement will help.
2) Barrel harmonics (bigger reason). Just like tuning a load to a rifle, weight on a barrel can cause groups to tighten or grow larger. Look up “barrel tuners”. Lots of 22 guys run them.

Threading a barrel in the traditional sense/pitch can cause the bore to open, but guys are still getting sub .1moa groups from those barrels. And while we know this does happen, you’d need to test an unthreaded barrel and then the barrel post threading to determine if there is any real negative impact based on the precision that the system can generate (rifle, shooter, ammo). The load may also need to be tweaked due to changes in barrel harmonics that may occur from weight reduction during threading.

The brake or thread protector isn’t constricting the barrel back to the previous diameter, but they will change the harmonics. You’ll see this with a thread protector that comes loose during a string of fire. The POI will begin to walk as the protector does on the barrel. I’d never advocate shooting extended strings with a thread protector on if really going for precise groups.