Hey guys. I was looking at pics of the XM177E2, and I was wondering:

Why didn't they just use a barrel the same length as the E2 barrel, with no moderator.
I know the moderator was put on to make the rifle "sound" like a 20" upper so the enemy wouldn't know Spec Ops guys were in the area...

What I don't get is why not just make the barrel as long as the XM barrel w/moderator and just use the A1 style flash hider? Basically a 14" BBL with a FH on it instead of an 11.5" BBL with a moderator?

Seems to me they lost velocity by using the short barrel with the moderator, and a longer barrel w/a FH would  have sounded like a 20", I think??  


And lastly, how long is the barrel WITH the moderator on a real XM177E2, is it close to 16" from bolt face to muzzle?  


Also, why did they change from XM177 to XM177E2? Were the short barrels causing cycle problems, or lack of velocity, or???


THANKS!!!!

JP

I'll answer what I can based on my limited knowledge.  The XM177E2 is an 11.5" barrel with a 4.5" Moderator (deemed a sound sup. by BATF).  The OAL I'll assume would be between 15.5" & 16".  

It started as a 10" Commando.  The 4.5 Mod was added in an attempt to reduce the noise & flash to that of the standard rifle.  

"Improvements to the XM177 included an add. 1.5" of bar. length (XM177E2) which, when mated with a redesigned Colt noise & flash Sup., offered the best poss. trade-off between versatility & increased noise & flash"- The Black Rife.

The Military must of learned something, since now they issue the 14.5 barrel.

Take your pick between urban legends.

- The VC could recognize when a SF group was operating in the area because of the distinctive sound of their carbines without the moderator, so Colt tried to make the carbine sound more like the rifle.

- the noise was deafening the SF soldiers

- the fireball at night destroyed night vision or gave away their postion even more

These are the ones I have read and heard over the years.  Who really knows which one is right.

Quoted: Take your pick between urban legends.... - the noise was deafening the SF soldiers - the fireball at night destroyed night vision or gave away their postion even more

That's my picks

height=8

Quoted: The Military must of learned something, since now they issue the 14.5 barrel.

True true...

Is that 14.5" + the 2" for the A2 flash hider, or 14.5" with the flash hider?


J

Quoted: Quoted: The Military must of learned something, since now they issue the 14.5 barrel. True true... Is that 14.5" + the 2" for the A2 flash hider, or 14.5" with the flash hider? J

The current M4's are 14.5" + FH.  As are a lot of the LW barrel builds (723, GUU).  This allows the use of a Bayo.  If you really want to learn about the AR, pick-up the books Black Rifle 1 & 2.

Quoted: Take your pick between urban legends. - The VC could recognize when a SF group was operating in the area because of the distinctive sound of their carbines without the moderator, so Colt tried to make the carbine sound more like the rifle. - the noise was deafening the SF soldiers - the fireball at night destroyed night vision or gave away their postion even more These are the ones I have read and heard over the years.  Who really knows which one is right.

Doesn't the XM177E2 still have that "starburst" flash even with the mod.? That's what I've heard.

height=8

Doesn't the XM177E2 still have that "starburst" flash even with the mod.? That's what I've heard.

The replica ones do, for sure.


J

Quoted: What I don't get is why not just make the barrel as long as the XM barrel w/moderator and just use the A1 style flash hider? Basically a 14" BBL with a FH on it instead of an 11.5" BBL with a moderator?

Well look at the progression.  You start off with a 10" barrel with a basic flash hider, then you get a 3" moderator, then you get a 4.5" moderator, then you get an 11.5" barrel, then you get a 14.5" barrel with a standard flash hider.  This whole process starts out in 1965 and gets to the 14.5"/A1 FH combo by 1973, so its not like people weren't essentially working toward what you're getting at, they just essentially tried everything in between before getting there.

Quoted: Quoted: What I don't get is why not just make the barrel as long as the XM barrel w/moderator and just use the A1 style flash hider? Basically a 14" BBL with a FH on it instead of an 11.5" BBL with a moderator? Well look at the progression.  You start off with a 10" barrel with a basic flash hider, then you get a 3" moderator, then you get a 4.5" moderator, then you get an 11.5" barrel, then you get a 14.5" barrel with a standard flash hider.  This whole process starts out in 1965 and gets to the 14.5"/A1 FH combo by 1973, so its not like people weren't essentially working toward what you're getting at, they just essentially tried everything in between before getting there.

An excellent summary.  I would bet that the original idea was to chop the barrel to half the length (20" to 10") wihout any great regards to the ballistics/flash/sound issue (it coudl have been as simple as some Special Forces guy saying to a Colt rep "hye, nice rifle, but it would be a lot handier if the barrel was about half the length...), but then they ran into the problems as mentioned and the solution as mentioned.

If you separate the upper and lower (with telestock), and screw off the moderator, the gun can be stored in a very compact space, such as in an aircraft survival pack. I think this might have been the origins of the short barrel with moderator deal.

Quoted: If you separate the upper and lower (with telestock), and screw off the moderator, the gun can be stored in a very compact space, such as in an aircraft survival pack. I think this might have been the origins of the short barrel with moderator deal.

The Moderator is attached according to the Manual with 15-20 pounds of Torque. Not really field expedient to remove by hand. All you have to do is stand near someone doing a mag dump with a 10in barrel to apprecate the sound made from a "full length" barrel.

Quoted: If you separate the upper and lower (with telestock), and screw off the moderator, the gun can be stored in a very compact space, such as in an aircraft survival pack. I think this might have been the origins of the short barrel with moderator deal.

The CAR-15 Commando SMG and Survival Rifle come out about the same time.  The survival rifle actually had a fixed stock of a unique type and an abbreviated pistol grip plus either a 3" moderator or a conical flash-hider (ala the M3 SMG) in order to fit in the "box" the USAF had in its requirements.  To my knowledge, neither the CAR-15 Survival Rifle nor the Stoner 63 Survival Rifle were ever fielded, and the USAF pretty much stuck to their existing survival weapons.