Put it on the 551 again, and pay closer attention. You'll notice a wiggle, if you don't have the closer snugged-up. I would not shoot the gun, and would say that it does not "work". Measure the OD of the 551 hider, and compare to the hider on your Colt. The 551 is smaller.

The bayonet-defeating tactic you mentioned is valid, but only as it is applied to the 550/PE90, as the 551 was already a reduced OD.

Mine 551-2 SP is notably smaller in OD and length (it's a 16")

As far as I can tell, the 16" 551 would have fallen victim to the "neutering" he previously mentioned, concerning potential bayonet attachment. The standard 551 with ~14" barrel has a longer hider, but still slightly narrower than NATO 22mm, even in an unaltered state.

Based on the barrels available to me for measuring, which is one 553LB, three 551 ~14" barrels, and one neutered 550 barrel, the measurements are as follows:

553LB (NATO spec): .864"
551: .844"
Neutered: .833"

I "mounted" my HALO on a 551 again. As Dan previously said, it will attach to the gun. But I maintain that just because you can doesn't mean you should. There is noticeable slop in the fit between the ID of the silencer and the OD of the hider. .020" of slop actually, based on my measurements. Another thing to note is the closer is designed to snug against the flat rear face of an A2 birdcage, not a tapered surface like the backside of a 551 flash hider. The sharp edge of the closer will certainly gall the rifle's barrel behind the hider, and the closer may even experience warping, after repeated on/off cycles, due to it riding up that taper.
When I eyeballed it, it seemed concentric. But I will NEVER put even one round through that setup, and I would recommend no one else do it either. It was not meant to be and it does not work.

What's old is new again.

https://sigforum.com/eve/forum...10055444&s=674608412

I came across that thread a few hours ago (and previously, years ago), in my search for more ACTUAL INFORMATION on the use of a HALO on a 551. Searches yield only rumors of a 551-spec HALO from Gemtech, based on what is seen in the HALO manual and some fruitless phone calls to Gemtech, and incorrect information perpetuated on a few discussion forums. The bottom line is largely stated in my previous post, but I will add that the mere fact that a 551-SPECIFIC HALO was deemed necessary by Gemtech at all proves that the available models don't work properly on a 551. Not to mention that, despite what people speculate may "work", there are no actual reports from the range. I suspect largely because no one wants to put a round through something they know isn't correct. When it comes to silencers, and guns in general, sometimes close enough isn't good enough, and .020" can go a long way.

Where the OP's original question is concerned, I think I ably answered it in my first reply, which I based off my real-world experience.

Oh, and I am confused as to what that image is supposed to mean, in the context of this discussion. It is an image of a neutered 550, with a technical drawing showing dimensions of a proper one, when we're talking about a 551. But it doesn't matter, I guess. So never mind.

quote:

Originally posted by KSGM:
I highly doubt they will. If they could import, it would be a different story, but they can't. I don't think they'd bother tooling-up and building such a niche silencer in their US facility.

I guess none of these will work either so I guess im shit out of luck for a can on this rifle.

Hold the phone! I just saw you added a picture to your original post! Your flash hider is different than my 553LB, and you should be good to go!

My hider resembles the 550, in that it lacks a flat spot, and has two narrower, shallower, grooves. Yours, having a flat and a larger groove will work with a few different cans, so long as it is 22mm.

HALO, M4SD, GP-NATO, etc. Go get 'em! If you wanted to be super cool, one of those B&T Rotex cans should work too.

I think the GP-NATO is worth a look, as they say it employs an improved baffle stack. As previously stated, I'd stay away from current-production Gemtech. Griffin is really the way to go, when it comes to NATO-mount with a collar or gate. Either should work on your gun.

Dang. And now I am super jealous of you and your gun. I guess I got one from before they made that awesome change. Boo.

And now I am wondering if current production 551s also have this revised muzzle. That would be awesome, but would also suck, because I don't have one.

This message has been edited. Last edited by: KSGM,

Sweet guys! As always thanks for the info!!

quote:

Originally posted by KSGM:
Why are current import 551s, and prior import LE/GOV't guns (which wouldn't have been subject to said bayonet silliness) also smaller OD then?

So your 551-2 SWAT is a NATO-spec hider?

Only the 16” OAL barrel 551s are the narrower diameter. As to why, I would guess it’s due to SAN finding new old stock barrels.

quote:

Originally posted by JoshNC:
Only the 16” OAL barrel 551s are the narrower diameter. As to why, I would guess it’s due to SAN finding new old stock barrels.

I measured my new-production JDI 551 flash hider, and three older 551 flash hiders. They are all smaller than NATO spec. If you have a 551SB, put the calipers to it. I will be very surprised if it is .864".

OP,
If your muzzle looks like that pic in the first post, you can use this Griffin NATO adapter.
https://www.griffinarmament.co...-375x24-suppressors/
That is assuming one of your cans is threaded that pitch, or you buy one that is.

Also, as an amendment to my previous post, the Griffin M4SD will NOT work without modification of the barrel or the gate latch piece of the silencer.

Update. Paid for the B&T Rotex X in July with Silencershop. Took a chance on the efile system being overloaded with amnesty paperwork and submitted a paper form. Approved and picked up the can today after 113 days. Christmas in November!!

[url=https://postimg.cc/BtFFXgDP]