I got me one of those Rearden FHD flash hiders because I converted my YHM Resonator K to plan B.
https://www.reardenmfg.com/product/fhd-flash-hider/

This flash hider does not need to be specifically timed so no shims needed for that aspect. However, the notes say:

quote:

Note: your barrel may require a shim if the manufacturer did not put a thread relief on it.

I am not sure what a thread relief means. I presume it means there is just a smidge of non threads prior to where the full contoured portion of the barrel starts.
This is going on an Aero precision factory gun and this is what my muzzle looks like.
I don’t believe I need a shim from looking at the threads on the device and the threads on the muzzle. There appears to be a non threaded shelf on the device that mates with that shelf on the barrel after the threads.


Also half the world says use some sort of rockset or thread locker and the other half of the world says not to.
What should one do?

A couple of my own thoughts.

I had a similar TBAC muzzle device loosen in use, and with which I had used only a little blue Loctite to secure it. After that experience I used the red stuff and more of it when reattaching the device. That was recommended by the TBAC rep when I contacted them for advice.

If the device were mine and there was any chance I’d ever want to fire the gun from the prone without a suppressor attached, I’d want the device to be timed with one of the “prongs” (or whatever they are) at the bottom of the orientation, rather than one of the slots. That would minimize the downward blast that could blow up dirt/debris. I once used a TBAC flash hider on one of my rifles. Its design made it impossible to prevent some downward muzzle blast, and I quickly changed it to a muzzle brake with a closed bottom.

Trigger Warning for anyone who is offended by posts that use information from AI sources, because I got this from Gemini AI:

“In machining and firearms manufacturing, thread relief (also called a thread undercut) refers to a small, unthreaded groove cut into the barrel directly behind the threads, right where they meet the shoulder of the barrel.

“When a machinist cuts threads into a barrel, the cutting tool cannot stop instantly at a perfect ninety-degree angle against the shoulder. Without a relief groove, the last thread or two would taper off and be incomplete.”

I don’t see what appears to be the groove in your photo above.

Rocksett that bitch, you don’t want to remove your can some day and find the muzzle device came off with your mount. There is endless derpy debate in the NFA community about that and the whole “yOu jUsT HaVe tO toRQuE iT pRoPerLY” crowd loves to act smug about it, including Rearden himself. Thing is, he ain’t gonna be removing your stuck muzzle device from your mount if happenstance decides it’s going to happen anyway, so I go ahead and use a tiny dab of Rocksett and haven’t had a problem. The real issue, supposedly, is using Rocksett without torquing to spec, but you know what? I have just cranked mine down with Rocksett and moved on with my life. Zero problems.

It’s just one more thing for people to overthink and bicker about.

Oh. Don’t use Loctite red, heat deactivates it, and guess what gets hot enough to do just that on an aggressive enough firing schedule? Rocksett and similar use silica and deactivate using water. You can just soak it or boil it to remove it if and when. Easy.

FWIW, there is a heat-resistant red Loctite which was what the TBAC rep recommended when I asked about my muzzle device coming loose. I decided not to use that variety because the device was on a bolt action rifle and was never going to get hot enough to affect what I used.

I am not making a recommendation either way, and perhaps Rocksett is the best option. On the other hand, a friend had a barrel with a muzzle device that was, according to SIG, secured with Rocksett. He soaked it for an extended period and then we boiled the ever-lovin’ out of it with no success at removing it. He finally sent the upper to SIG for them to remove it.

Sigfreund, it hard to tell in the picture but that last portion that looks like threading just before the shoulder is not threading.
It’s hard to tell in the picture but it goes fully in a concentric circle prior to the should. Not a threaded twist, so it does fit the AI description of a thread relief.

Also, just by hand threading it once I torque it down one of the prongs will be straight down.

Got some Rocksett on the way.

quote:

Originally posted by sigfreund:
I am not making a recommendation either way, and perhaps Rocksett is the best option. On the other hand, a friend had a barrel with a muzzle device that was, according to SIG, secured with Rocksett. He soaked it for an extended period and then we boiled the ever-lovin’ out of it with no success at removing it. He finally sent the upper to SIG for them to remove it.

Yeah, I think I recall you posting a thread about that. Someone did, anyway. I can't speak to what SIG does from the factory, but I can tell you first hand that CZ is renowned for their prodigious use of thread locker on the Scorpion and Bren 2. Guys have damaged and even destroyed parts because of it. I see a lot of recommendations to use heat, which of course, does nothing to release a silica-based threadlocker. I wound up using PB Blaster, three applications over the course of three days on the handguard and barrel screws on my Bren 2, then a rubber band stretched over the tip of the Torx bit in screws I had started to round out. They came out with zero effort, and the threadlocker was something the look and consistency of fresh toothpaste.

From a liability standpoint, I can understand manufacturers telling assemblers to use enough threadlocker that they have to wipe off the excess once the parts are fitted. I was just such an assembler instructed to do exactly that in a former job. For the end user? As I said prior, a small dab is more than sufficient, and if/when you want to remove it, you can either soak, boil, or even lower effort, just hit it with something like Kroil or PB Blaster several days in a row and it comes right apart.

quote:

Originally posted by Black92LX:
Got some Rocksett on the way.

Small. Dab.

I put a 3 prong f/h on my sig 556 the 3 ports were angled so the gas would force the f/h in the same direction as tighting it as stated by the manufator. It is different than the one in your picture.

The image on the left is undercut, "relived", on the right is not.
Looking at your picture, I can't tell if your barrel is relived or not.

It is similar to the one on the right the ledge/collar prior to the shoulder is the same height as the threads.
So I guess I’ll toss a shim on there.

I have a shim kit for timing muzzle devices and use rock set on the threads.

https://www.amazon.com/dp/B0CY..._dt_b_fed_asin_title

Thread relief allows female threaded parts to be able to thread all the way onto a male threaded part without binding up at the end. If cut first, it also makes adding threads much simpler and cleaner. Technically, thread relief should be of a smaller outer diameter than the threads, so there is a difference between thread relief and a portion of just unthreaded material that is the same diameter as the threads.

Here's a good comparison to go with D_Steve's drawing. I would say yours does not have it.

^^^^^^^^^
Thanks much, that is exactly what is needed. Mine is nearly identical to the top picture above so shim it is!
I have some that came with my YHM muzzle devices so I’ll toss one of those on when my Rocksett arrives today.

Rocksett is removed with steam and not heat if you want to remove the device.

I have a mini travel steam iron that I use.

I wonder if most factory threads don’t have the relief because it’s assumed that they will usually be used with shims or crush washers to time a muzzle device.

I thought it was Shims if it needed to be timed and crush washer if not?

Or maybe I'm being that guy. But I'd use a crush washer and Rockset if you don't need to time it. Shims if you need to time it.

quote:

Originally posted by myrottiety:
But I'd use a crush washer and Rockset if you don't need to time it. Shims if you need to time it.

Guys. This isn’t standard advice about a muzzle device, this is for mounting a suppressor. The only time you should use a crush washer for a muzzle device with a suppressor is if you want to virtually guarantee a baffle or endcap strike.

NEVER use a crush washer with a muzzle device that you’re going to be mounting a suppressor on. Shims only, and only if necessary.

quote:

Originally posted by P220 Smudge:

quote:

Originally posted by myrottiety:
But I'd use a crush washer and Rockset if you don't need to time it. Shims if you need to time it.

Guys. This isn’t standard advice about a muzzle device, this is for mounting a suppressor. The only time you should use a crush washer for a muzzle device with a suppressor is if you want to virtually guarantee a baffle or endcap strike.

NEVER use a crush washer with a muzzle device that you’re going to be mounting a suppressor on. Shims only, and only if necessary.

Ahh... good point. Wasn't thinking about it being a can mount.

I don’t have the experience that some do here, but I use crush washers to time things like flash hiders or brakes that won’t be used with suppressors. They are much less difficult to use than shims.

It's always something. My Rocksett arrived late last night.
So I figure I'd slap that puppy on this morning. Well, Rearden decided to use 13/16 wrench flats instead of the usual 3/4.
Low and behold I don't own a 13/16 wrench guess I'll just use the adjustable wrench.
So I go grab my shims and hot damn they are all for a .30 cal.
So have to order some shims and a wrench!!!

Well, I don't have a standard crows foot set just some flare nuts so I ordered a set so I can torque the muzzle device correctly and ordered the shim kit listed above.

Hopefully that will do it.

Turning in to a costly venture. I also bought the Wheeler version of the Geisselle reaction rod.
I have a clamshell and upper receiver pin blocks but more maximum rigidity one has to remove the optic. Folks also say for twisting on and off the muzzle devices it's better to use a reaction rod style.
So, there is that. Plus, the muzzle device (more to come) and the hub adapter.
To which I did not have a 1 1/4" socket for so I bought a Kobalt set of 1" plus sockets for $20.

What a lovely hobby this is!!

Well, you’ll be set for next time.
That’s what I tell myself.