I've been looking at 16" midlength AR15 uppers and I've noticed that none of them have the "stepped" barrel (I believe this is the M4 profile). Why is this? Can you have an M4 profile barrel on a midlength upper? Or is that part of the barrel simply covered up by the handguards in the midlength system?
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April 7, 2010, 07:32 AM
The mid-length barrel has its gas port in a different spot. The whole contour is different.
The "step" in an M4 profile barrel has to be a certain distance from the chamber end for proper mounting of the grenade launcher, which is the actual original purpose of the "step". In a 16" civi M4 profile barrel, the extra length is added "heavy" contour length between the step and the flash hider... the step is still the same distance from the chamber.
With a midlength gas system, the gas port is moved ~2" forward of where it is on a carbine gas system. I don't know the *exact* dimensions, but this would likely put the FSB into the "step" on an M4 contour barrel. Therefore you can't have the step. Putting a step forward of the FSB on a midlength gas system barrel would be even more useless than it is on a 16" civi market M4 profile barrel, since the dimensioning alone would make the step completely useless for its intended purpose.
April 7, 2010, 10:00 AM
I think NY has your answer.
April 7, 2010, 04:13 PM
Just adding, the profile of the midlength barrel in ArmedBear's the top pic is called a "Government Profile" and it is the same profile as a 20" M16A2/M16A4 barrel (just shorter obviously). It will be just as light as an M4.
April 7, 2010, 04:21 PM
To pile on, the "M4 profile" is only needed if you want it for aesthetics or actually plan on mounting an M203. Otherwise, just go with whatever thickness you want (to sum up 500 threads on barrel profile, heavy for target shooting/precision/varmit use, light for stand-up "fighting carbine" use). The step does nothing functional if you don't own a M203.
April 7, 2010, 04:29 PM
One more pile-on...:)
You can get M4 feed ramps on other barrels, and you can get M16 feed ramps on M4-style barrels. Apart from appearance, there's nothing inherently special about a civilian M4-looking barrel.
When it comes to tacticoolness, unless you actually have an M203, the midlength barrel offers something better than the 16" M4gery does: you can mount a standard M7 or M9 bayonet (or a rubber one as used by Airsofters, just for fun). I have an M7 for my 20"... Say what you will, but everyone who plays with it, wants to get one of their own....:D
April 7, 2010, 08:07 PM
Back on top of the pile. :)
the midlength barrel offers something better than the 16" M4gery does: you can mount a standard M7 or M9 bayonetYea boy.