XM177: 5.5" moderator straight wall or conical?

https://www.tntesales.com/xm-177-gau-5-5-5-flash-hider-phosphate/

https://www.tntesales.com/one-piece-xm-177-gau-5-5-5-flash-hider-phosphate/

I’ve attached a picture of the conical inside version. Would this show any advantage over a straight wall ID 5.5" flash hider? I was thinking possibly more accuracy…

I posted this in the Vintage section but realized it really is just a general question. FH is 5.5" long but there are two options…

One is a straight wall inside (tube that meets the bore) and then there is the one below which is a conical tapering interior. What benefit would one have over the other? I asked TNT and they said “weight” :rolleyes:

Well, an advantage is it looks like a suppressor for an XM177E2. It probably does not weigh any more than one of those either.

A disadvantage would be it will not reduce the over-pressure of a short barrel like the XM177E2 suppressor, and may not reduce flash to the same extent.

Maybe I read you wrong but if not, I want to clarify. These are the two flash hiders in question…Notice the drawing difference in them. Appearance and dimensions are identical. Only difference is the internal design.

If you understood the differences then I misunderstood you

This is the most Mickey Mouse shit ever but I drew some diagrams to explain my thoughts here. Technically wouldn’t the conical FH be more accurate due to the gases being controlled in a better design and not just floating around in the chamber?

My guess is the full diameter one might give you a slight boost in back pressure like the old Noveske Flaming pig. But the more turbulent gas release might result in more flash.

But I also wonder if the full diameter resign is just a newer production design to eliminate the step down design to save time/cost?

Maybe I should buy both and do a comparison at the range before pinning and welding. I’m mostly concerned with accuracy. I’ll just get both and make a thread on my findings.

A muzzle device with an enclosed expansion chamber might be classed a suppressor by the ATF . . .

Or are you talking about something like this? It that case there wouldn’t be much, if any difference, other than weight.

The Griffin XM Linear Comp had a single baffle and is effective giving you back-pressure (for short barrels) and a little flash suppression.

A straight extension serves as a “Viz Mod” (visual modification) but really doesn’t do much for you (functionally). They were all the rage in the 80s up to the '94 ban.

If it’s not machined true coaxially it can make for larger groups (like a bad crown).

//youtu.be/rWXrrDAUYwU

What the Colt looks like inside (the Griffin looks like the external body on the right with no other baffling):

The AWC Hyperdyne was similar – just a simple vented, closed tube:

All that. Which is why you don’t see XM177 type flash hiders on current 10.3/11.5 SBRs unless you are building a clone. For the same space you could mount a SF mini and get actual suppression.

Problem is I’m building a clone

Options:

  1. By a wide margin. Find an over the barrel version you can get pinned to a 14.5” barrel.

  2. Ask the manufacturer why they make two different designs and what they recommend for your needs.

Better do the testing on a pistol pistol lower…

Todd’s number 1 by a wide margin. There are nuances of course but I predict big flash and the thing is, the flash makes its own noise. So, if possible, don’t give up velocity and replace it with more flash, more noise, and less reliability. Unless you want to also replicate ballistics for research purposes. but-- we’ve had old Olympic guns in class that had the long FH and they basically give the worst of all worlds.

Which one are you talking about? And who is Todd?

This number 1

Again cloning it. I don’t care much about flash or noise it will be a range toy. I am nervous about horrible accuracy though with a 5.5" FH

With that #1 option it will look the same but give you another 150-200 FPS which some day you may be glad you had, plus your accuracy concerns are gone. There is a guy that specializes in the clone thang, bet he has the preferred combo whichever you choose, but I can’t think of his company name just now. Charlie’s Clones maybe?

Ah, in that case I’d go with the Griffin that sinister recommended.

They aren’t made anymore

https://nfatalk.org/forum/showthread.php?t=12761