Threaded too long? Armalite M-15 Comp AR

[carbonbased]

So, some time ago I got a great deal from PSA on a new Armalite M-15 Comp AR 18”. It came threaded from the factory.

Bought a RC3 and the requisite Surefire muzzle device. In my case, that was the 4 prong flash hider.

A year later, still waiting for that damn suppressor to get out of jail (contacted my congresswoman to talk to the atf).

So I have had no use for the flash hider as I shoot 100% suppressed. Suppressor works fine; barrel threading seems to be concentric enough to give me zero baffle strikes. Two suppressors shoulder up fine.

Ok, back to my plight. Bored, I go to thread the flash hider on, and it won’t go flush to the shoulder! It’s pretty close, but I see a silver of daylight peaking through. I’ll measure it tomorrow with a feeler guage, but the gap looks like the thickness of 2 pieces of paper.

Confused, I clean off any crud. Still won’t go.

I break out my calipers with the depth gage.

Flash hider: The depth from shoulder to the bottom is ~0.625”

Length of threading on the barrel (muzzle to shoulder). ~0.625” or maybe a hair over.

TBAC has thread specs that state the threading should only be 0.600” long.

Thunder Beast Arms Corporation [TBAC] | Tech | THREAD SPECIFICATIONS

Now, maybe this is why PSA was blowing these out? I need to call Armalite tomorrow about the dumb length of threading, but is my info off base?

 

[Jsp556]

Stupid question but do you have the tapered spacer installed?

I’ve never installed a Surefire md without using it.

Ill measure a Krieger from Krieger direct and share the length of the threaded muzzle.

ETA:
Krieger 556 shoulder to muzzle = .626”

ARP 556 Socom shoulder to muzzle = .622”

Craddock RTR 6.5G = .571”

 

[sinister]

 

[carbonbased]

Stupid question but do you have the tapered spacer installed?

Oh shit, I need to look at the package!

< running back to gun room >

I think we have a Bingo!

Since this is my first muzzle device and it’s not one that needs to be timed, I didn’t even think of spacers. Thank you! Saved me some grief.

For indexing on the barrel shoulder, I need to use their chamfered spacer. If that isn’t enough, I could throw on a number of timing shims for a bit more thickness.

Didn’t realize one can also index off the muzzle face. In that case one adds just the shims.

I’ve always indexed suppressors off of the shoulder. I remember some Euro suppressors possibly indexing off of the muzzle face.

How do you dudes index your Surefire muzzle devices?

 

[carbonbased]

Yeah, that’s the other threading standard I’ve seen floating out there. For shoulder indexing, .600” to .620”.

It appears my barrel was threaded way too long.

 

[Jsp556]

Oh shit, I need to look at the package!

< running back to gun room >

I think we have a Bingo!

Since this is my first muzzle device and it’s not one that needs to be timed, I didn’t even think of spacers. Thank you! Saved me some grief.

For indexing on the barrel shoulder, I need to use their chamfered spacer. If that isn’t enough, I could throw on a number of timing shims for a bit more thickness.

Didn’t realize one can also index off the muzzle face. In that case one adds just the shims.

I’ve always indexed suppressors off of the shoulder. I remember some Euro suppressors possibly indexing off of the muzzle face.

How do you dudes index your Surefire muzzle devices?

I time mine so the index tab is at 6 o’clock. Even the flash hiders. I don’t think it’s necessary for the flash hider but that’s how the instructions show all the other devices timed.