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Old July 18, 2010, 10:34 PM   #1
Blackops_2
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Quick AR/M4 question.

Alright so i'm thinking about how the colt m4 is 14.5. But is it 14.5 with a 2" flash hider. Or is the barrel just 14.5 with a added 2" flash hider making it OAL 16?
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Old July 18, 2010, 10:40 PM   #2
superchi
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Are we talking about military M4s or civilian AR-15s?

In regards to AR-15s, they can go either way:
-14.5" barrel with a standard flash hider that is not pinned and welded would be considered not legal length unless it is registered as an SBR
-14.5" barrel with a flash hider that can make the overall length reach 16" when pinned and welded would be legal.

I assume that NFA rules do not apply to soldiers in the military using the M4 rifle so legal length is not something to be considered
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Old July 18, 2010, 10:47 PM   #3
Blackops_2
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Both but i'm talking strictly length. In other words. If i build a ar-15 with a 14.5 inch upper with a permanent flash hider, is it the same length as a Colt M4 (military). Or is the M4 OAL of the barrel 12.5 + 2" flash hider making it 14.5"?
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Old July 18, 2010, 10:58 PM   #4
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The military M4 barrel is 14.5" without the FH and the flash hider is not permanently attached. If you want to get to legal length with a standard A2 or A1 flash hider your barrel should be 14.7".

Some people stick a spacer on a 14.5" to get the OAL to legal with a standard FH.

There are FHs that will get a 14.5" barrel to legal OAL when permanently mounted; Phantoms are popular for that application as are extended A2s.
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Old July 18, 2010, 11:04 PM   #5
Blackops_2
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I realize the actual barrel of the Military M4 is 14.5. Does that measurement of 14.5 include the flash hider? If it does then it would technically make it roughly the same size as a 14.5 AR with a permanently attached FH would it not? See when i look at a M4 and then look at a build that is 14.5 upper with permanently attached FH the M4 looks shorter. In other words is the length of a M4 barrel the same as a 14.5 AR upper with permanently attached FH?

So in other words the M4 barrel length is the same as a 14.5 with a permanently attached FH?

Same thing goes for 16" mid uppers. Technically if your measuring with the FH they are roughly 18" correct?
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Old July 18, 2010, 11:18 PM   #6
noyes
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Overall Length: 34.75” [88.27 cm]

http://www.bushmaster.com/catalog_mi...MCWA2F14M4.asp


OVERALL LENGTH 33 in (84 cm)


http://www.colt.com/mil/M4_2.asp
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Old July 18, 2010, 11:31 PM   #7
Blackops_2
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If you can find the overall length of a 14.5 AR with a permanently attached FH. Then i could compare it would answer my question.
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Old July 18, 2010, 11:49 PM   #8
noyes
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4rd barrel down

14.5" Bushmaster M4 Type Barrel Assembly
This Law Enforcement / Military carbine barrel is under the 16" legal minimum for semi-auto rifles, and can only be installed on registered full autos or legal short barrelled rifles. It is machined for the addition of the M203 grenade launcher and has the narrow "government" profile under the handguards for light weight (like the original A1 rifle barrel).


6th barrel down

14.5" Bushmaster M4 Type w/ Izzy Compensator Barrel Assembly
This assembly - with a factory pinned and welded Izzy Compensator - meets BATF requirements for total length (barrel and compensator) of 16" or over for semi-auto rifles. Includes Barrel, Bayonet Lug, Sight, Handguards, Shields, Gas Tube, Delta Ring and Compensator - ready to assemble into that perfect 3 Gun Match carbine, plinker or home defense special.

http://www.bushmaster.com/products.asp?cat=7
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Old July 18, 2010, 11:58 PM   #9
Blackops_2
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So the Military M4 is actually 14.5 counting the length of the FH. So therefore the actually barrel length is shorter than 14.5? That or the FH is less than 2"
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Old July 19, 2010, 09:35 AM   #10
Technosavant
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Quote:
So the Military M4 is actually 14.5 counting the length of the FH. So therefore the actually barrel length is shorter than 14.5?
No.

The military M4 barrel is 14.5" sans flash hider. Since the flash hider is not permanently attached to it, it is not included in the overall barrel length calculations.

Take that same barrel and permanently mount a flash hider that extends the length to at least 16", and it is now legal for use on a non-NFA civilian rifle.

A civilian legal non-NFA barrel with a removable flash hider is at least 16" to the muzzle crown- when you mount a flash hider to it, the actual length is extended, but since the hider isn't permanently mounted, the added length doesn't count.
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Old July 19, 2010, 10:20 AM   #11
Blackops_2
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Nice. So a M4 with the FH attached and a 14.5 AR upper with a FH permanently attached are roughly the same size correct?
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Old July 19, 2010, 10:21 AM   #12
noyes
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A2 Bird Cage Flash Suppressor
Standard 5 Slot Design for threaded muzzles (1/2" x 28 T.p.I.) without a bottom slot so it won't create a dust signature when firing from the prone position. A Peel Washer or Crush Washer is required for correct installation timing. Note: Even if pinned on/welded over, the A2 Birdcage Flash Suppressor is NOT long enough to make a 14.5" barrel legal for use on a semi-auto rifle.



It's the Lenght of the MB , FH that you put on the 14.5 " barrel


http://www.bushmaster.com/products.asp?cat=8


A 14.5" barrel is 14.5" the lenght of the muzzle brake / flash hider will give you a total lenght.

Example;

14.5" barrel + a 1.5" muzzle brake / flash hider = 16" total lenght

14.5" barrel + a 3" muzzle brake / flash hider = 17.5" total lenght

Last edited by noyes; July 19, 2010 at 10:40 AM.
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Old July 19, 2010, 01:16 PM   #13
Technosavant
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Quote:
So a M4 with the FH attached and a 14.5 AR upper with a FH permanently attached are roughly the same size correct?
Assuming identical flash hiders, then yes.

However, as pointed out, the standard bird cage flash hider, by itself, will not result in a non-NFA barrel, even if permanently attached. So you really couldn't use an identical flash hider on the thing. You'd need something a shade longer in order to hit the magic legal 16" length if you didn't use extra washers. I'd personally make sure you used a gunsmith familiar with the laws; the last thing you want is a Club Fed vacation for lack of a couple tenths of an inch because your gunsmith screwed it on too tightly.

The only real way to notice the difference between a military 14.5" barrel and a civilian legal one with a permanently attached identical flash hider would be to see if you could unscrew the hider.
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Old July 19, 2010, 02:37 PM   #14
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I love the actual length of the M4 thats what brought up the question. If i had the legal documents to get a SBR i would i like the look and handling of a SBR. I have plans for a BCM 14.5 pinned/welded with a AX2 FH. I would like it to be about the same length as a M4 which i'm guessing it will be after this discussion. Thats another thing when discussing barrel lengths, when i measure a barrel on AR i measure the FH too. So there for a 16" mid would actually be somewhere around 17+ i'm guessing.
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