View Full Version : XM177E2 Review with Griffin XM Linear Comp

9 August 2015, 03:22
The Griffin XM Linear comp was a neat project. It really was a hobby project for me. I was going to make 2 NFA moderators and then decided to make a small run of these so other people could obtain one.

One of the first customers to buy one was unhappy with his product. He didn't understand why his std wrench was too wide to fit. These are exact dimensional replicas externally - they require a thin wrench or the M16A1 armorers wrench to be installed. MACVSOG Operators stuck their SOG knives into the cuts in the flash suppressor and used that as a means of torquing them on and off. That does leave a mark.

These are also assembled, welded, OD turned, and melonite QPQ'd. This leaves them a little better looking than the original units which were welded by hand using tig with filler rod (no two were exactly alike). The QPQ looks pretty similar to the oxide or phosphate finish of the originals, but those originals would turn brown when fired and heated as some rust would occur- I kind of see QPQ as a major improvement myself - I didn't want a rust/patina brown colored muzzle device, but one of the nuances of the device with QPQ is it gets hot incredibly fast, burns off any protective oil, and then looks slightly irregular in finish until re-oiled. If a person is really a finish quality nut, they should probably look somewhere else, or realize that the XM moderators were low volume, wartime production muzzle devices.

9 August 2015, 06:13
I all ways love that design nice vid

9 August 2015, 08:21
Out of curiosity, what makes this non-NFA versus the original moderator? Is it the design of the vents?

9 August 2015, 09:17
There is no baffling internally and it was not designed to reduce sound but to reduce muzzle movement and rise inside the aesthetic and external dimensional envelope of the original device. It's a linear compensator. The original device had a monolithic baffle with 3-4 baffles and had coaxial chambers and porting and was designed to reduce sound and flash. The vents I think you are referring to are the slots in the flash suppressor which was added in front of the moderator, which began life as a minorly functional mini sound suppressor on the Colt 607 carbine- a shortened telescoping A1 stock 10" carbine with cut down triangular handguards that I believe was fielded to dog handlers. That moderator had an ~.25" bore, and that was found to destabilize bullets, so the XM177 moderator not only added the flash suppressor to the moderator, it also punched the bore to .295".

I think the reasons the moderator existed were probably flash reduction and the Army wanting the carbine to be no more dangerous to operator hearing than the 20" A1. So the moderators dropped sound ~3-5DB's and reduced huge fireballs to a level more like we're familiar with on the 14.5" M4 carbine with A2.

The M4 carbine barrel was Colts answer to the NFA determination on the moderator- the military still wanted the M203 grenade launcher ready carbine with the ~15" barrel system length, and Colt didn't want the extra paperwork and export issues for foreign government sales.

The real XM moderator weighs 10.5 ounces - and that combined with the aluminum stock gives the XM177E2 a feel almost like a Thompson machine gun- it has a confident heft to it. When I picked up an XM177E2, at first I thought the barrel was heavy under the handguards.

9 August 2015, 11:49
Of course, no baffles. I should have thought of that. Thanks for the explanation. The whole kit looks sharp.