The closest thing to an M4 military rifle in a civilian model.

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HMFIC

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Ive heard that the shorter barrels on the M4's underpower the 5.56 round.is this true?

You'll obviously lose velocity as EZ said. That does translate to the rounds not fragmenting as much or at all if it gets slow enough either due to the inherant loss of velocity or just from the distance and slowing below proper fragment speeds.

But are you really concerned about that?

Re: Switching to 77 grain slow boolits that cost more and still fragment at the slower speeds (to a point) due primarily to the thinner jacket, I don't think I'd waste my time with that. They'd be good if all you needed to penetrate were flesh, but overall I wouldn't consider the tradeoff worth it.

So are you wanting something that's just got the look of an M4 or are you wanting M4 performance in total including using milspec ammo, etc... what are your concerns?
 

CamaroMan

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The upper I linked to with the 14.5" barrel has a permanently attached flash hider that therefore counts as barrel length making it 16.1".

^^^This is the way to go for max M4 authenticity. If you get a 16" barrel there really isn't any reason you shouldn't go with the mid length gas system IMO.

Also my 1x7 twist seems fine for 55gr haven't tried anything lower though. There may be negligible accuracy loss over the heavier stuff but I can't tell. Definitely no ripping bullets apart or key hole issues.
 

Norman

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As others have said get a 14.5 inch with perm. attached flash hider. If you go with a 16 inched get a midlength. A 16 or 14.5 inch barrel doesn't 'underpower' the 556, but it will shorten the range the round will fragment. IIRC it's around 100-150 yards, but don't quote me. For as close to M4 spec as possible I'd go with a Colt 6921 and permanently attached flash hider, or a Bravo company (BCM). For the best deal going get a BCM blemished lower, and a BCM permanently attched flash hider.
 

henschman

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the very closest to a military M4 you could get while keeping it semi auto would be a Colt 6920 with a 14.5" barrel, GI flashhider, and a SBR stamp. That would be GI spec except for the 3 round burst or full auto trigger group. If you want the issue quad rails, that is a Knights Armament Co. RAS. The issue rear sight is a Matech BUIS. The issue red dot is an Aimpoint Comp M2 or M4. The issue scope is a Trijicon TA31RCO-M150CP or TA31RCO-M4CP depending on whether you want the Army or Marine version.

If you want to go a little off mil spec but avoid all the NFA bullcrap with the $200 SBR stamp, registration, etc., you might go with a 14.5" barreled rifle with a permanently attached flash hider that is a little longer than the GI one, which brings total barrel length over 16" and avoids the NFA business.

I said Colt because they are the one who makes the military's M4s, but BCM and CMMG sell rifles that are equally mil spec.
 

Seadog

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If I recall right F&N made em for the army to but that may have been the A2 and not the M4.

Ive see alot and forgotten about as much. So I could be wrong
 

Wizard

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Ive put together a few ARs for people wanting an M4agy KISS rifle. The M4 I carry at work EVERY day is made by colt and has a 14.5" bbl which would be a SBR and require a $200 tax stamp. Most of the ones ive put together are 16" with either mid or carbine length gas systems. None have ever failed to function or come back to me for anything other than upgrades from the KISS parts.
 

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