View Full Version : Colt M4 VS M4A1 Carbine
Secretariat
10-30-14, 10:28
If I may ask , what are the differences between a Colt M4 and M4A1 carbine ? Is it true that a Colt M4A1 comes with a KAC rail hand guard while the M4 does not ? In regards to the upper receiver and barrel , how can I tell if it is a Colt M4 or a Colt M4A1 ? What markings should I look for in the upper receiver and barrel to know if it is an M4 or an M4A1 ? The reason for me asking this question is because I have an upper receiver and barrel of either a Colt M4 or M4A1 and I don't know which is which .
Thanks in advance .
Eurodriver
10-30-14, 10:34
There should be an NSN on the QR code on the magwell, but since you only have the upper... (poor reading comprehension on my part)
The M4A1 is 1005-01-382-0953
The M4 is 1005-01-231-0973
Another obvious difference would be that the M4 is burst while the M4A1 is full auto. Both should have KAC rails, but the M4A1 has a thicker barrel profile especially under the handguards. The barrel is the best way to tell from what you have.
Secretariat
10-30-14, 11:25
Where do I find those numbers?
Thanks.
It doesn't sound like you're talking about an issued rifle are you? While Colt did start branding their civilian ARs with "M4" on the magazine well not too long ago, as Euro said, the M4 has burst fire while the A1 has full auto. You can't just go out and buy either of them.
Secretariat
10-30-14, 12:30
Well , I only have the upper receiver and barrel and not the lower receiver . That is why , I cannot tell if it's it has a 3 round or full auto burst . As for the the rifle being issued , probably , the lower receiver from which my upper receiver and barrel came from , might have been . I don't really know but definitely , it is not a Colt civilian AR/M4 rifle . By the way , in the upper receiver , there is a laser mark "c" and "AF" .
Thanks.
Are you referring to the 6920 models with a 16" barrel?
3ACR_Scout
10-30-14, 12:43
Where do I find those numbers?
The NSNs don't appear on the upper - they are just used when ordering the components through the government supply system. The only way to tell the difference between the two uppers is by the barrel, because nearly all M4s were refitted with the KAC rail system years ago. The M4A1 has a heavier (thicker) barrel under the handguards with notches cut into the sides, as seen about halfway down this article in the comparison photo (M4A1 on top, M4 on bottom):
http://www.guns.com/2014/03/05/colt-lands-54-5-million-army-contract-m4-pip-upgrade-program/
Now having said that, the Army is starting to replace original M4 barrels with the heavier M4A1 barrel, so it's not guaranteed.
You can check to see if it's a civilian Colt barrel by measuring the barrel length. If it's more that 16" (about 17") including the flash suppressor, then it's the civilian version. If it's less than 16" total, well... PM one of us before replying.
Dave
midSCarolina
10-30-14, 13:10
My guess is that the M4 you are referring to is the generic LE6920 while the M4A1 is the Colt 6920 SOCOM since they rollmark the LE6920 "M4 CARBINE" and the 6920 SOCOM "M4A1". The barrel profile under the handguards of the "M4A1" will be the same thickness as it is after the FSB while the "M4" will have a barrel that is a thinner profile under the handguards. The "M4A1" also does come with the KAC M4 RAS or, more recently, Troy rails :p .
When I said issued rifle, I meant if you were currently serving in the military or law enforcement and they issued it to you. If not, then it is definitely not an issued rifle and not really an M4/M4A1. Those don't mix into the civilian world at any point. You can buy Colt rifles available to the public which come pretty damn close, but it sounds like you're pretty new to firearms (or at least ARs) and are under a common misconception.
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JBecker 72
10-30-14, 13:54
M4A1 SOCOM barrel on top
M4 government barrel on the bottom
This will be the only difference between the 2 uppers.
http://www.hunt101.com/data/500/M4_Barrels.jpg
Something else to note, if your barrel is 16" I'm pretty sure Colt does not put the slots in the barrel under the hand guards on the SOCOM. They only do this on the 14.5" SOCOM barrels. It's for mounting a grenade launcher.
sinlessorrow
10-30-14, 16:54
Different barrels. The M4 has the RO921 and the M4A1 has the RO921HB. The M4A1 also has an ambi safety(which is very nice) as well as a H2 buffer in the M4A1 vs the H buffer in the M4. Those will be the only civilian differences.
The differences have been pretty well covered here. I'll just add that there is a very noticeable weight difference between the M4 and M4A1 barrels if you're used to one and switch to the other. My unit was one of the first to get our M4s converted over to A1s, and the added weight was very noticeable (and being grunts, it was the first thing we complained about). I know they call it a "heavy barrel", and that's a name I have to agree with. :jester:
sinlessorrow
10-30-14, 18:36
The differences have been pretty well covered here. I'll just add that there is a very noticeable weight difference between the M4 and M4A1 barrels if you're used to one and switch to the other. My unit was one of the first to get our M4s converted over to A1s, and the added weight was very noticeable (and being grunts, it was the first thing we complained about). I know they call it a "heavy barrel", and that's a name I have to agree with. :jester:
Technically it is a medium weight barrel, and the M4 weighs 7.46lbs compared to 7.74Lbs of the M4A1. So .28lbs heaver.
Secretariat
10-30-14, 19:31
By the way , my barrel is 14.5 inches long . Anyway , Thanks a lot to the all of you for the time and your inputs . Really appreciate them .
3ACR_Scout
10-31-14, 02:37
When I said issued rifle, I meant if you were currently serving in the military or law enforcement and they issued it to you. If not, then it is definitely not an issued rifle and not really an M4/M4A1. Those don't mix into the civilian world at any point.
Since he's talking about the upper only, and not a complete rifle, I think it's conceivable that he has a take-off upper from a police or other organization's M4. I've seen a number of Colt 14.5" uppers pop up on GB that are described that way, including one that's currently listed as a former NYPD 1/9 twist M4 upper. I'm guessing it would be pretty hard to tell if this one's the real deal or an LE6921 upper, but it seems quite possible that former police uppers have been sold off from M4s that have been traded in or possible destroyed (e.g. an upper taken off an unserviceable lower).
Dave
I have a hunch it's just a standalone 14.5 upper like the ones Grant sells. He says it's probably issued, which means he has no idea.
Secretariat
10-31-14, 05:08
By the way , in the upper receiver , there is an engraved laser mark of a "C" and "AF" . Also , for your information , I don't live in the U.S.. I live here in the Philippines . I purchased this Colt M4/M4A1 upper receiver in 2008 . Anyway , what are the advantages of the thicker barrel of the M4A1 as compared to that of the slimmer barrel of the M4 .Also , what are the other advantages of the M4A1 over the M4 ?
Thanks again in advance .
PS. In a way , 3ACR_Scout is right , I purchased this Colt M4/M4A1 upper receiver and barrel from someone who was part or had connections with the U.S.-Philippines Visiting forces Agreement here in the Philippines . It is a take-off upper receiver of one of the Colt M4/M4A1 loer receivers used VFA exercises here
Anyway , what are the advantages of the thicker barrel of the M4A1 as compared to that of the slimmer barrel of the M4 .Also , what are the other advantages of the M4A1 over the M4 ?
The M4A1 with it's thicker barrel is more durable during sustained full-auto fire. It doesn't heat up as fast as the thinner barrel of the M4; of course once it does get hot it doesn't cool as quickly either.
3ACR_Scout
10-31-14, 05:49
Also , what are the other advantages of the M4A1 over the M4 ?
In addition to what ABNAK stated about the barrel, the only other real difference between the two models, as previously mentioned, is the full auto fire control group in the M4A1 vs. the 3-round burst FCG in the M4. While opinions differ on the usefulness of full auto fire, I think the general concensus on this forum is that the auto FCG offers a more consistent trigger pull when firing the weapon in semi auto. The 3-round burst FCG creats a variable trigger pull as it cycles, which has a negative impact on accuracy when firing on semi.
Having carried an M4 with a full auto FCG during my first Iraq deployment, I feel that the trigger is controllable in automatic fire, to where you can fire bursts of various lengths (2-round, 4-round, etc.) without being limited to the 3-round cycle. Whether or not that's useful is up for debate.
Dave
Secretariat
10-31-14, 06:49
For your information also , my M4/M4A1 upper receiver and barrel is partnered with a Colt M16A1 lower receiver.
Again , Thanks a lot for all your replies and time.
Secretariat
10-31-14, 06:49
For your information also , my M4/M4A1 upper receiver and barrel is partnered with a Colt M16A1 lower receiver.
Again , Thanks a lot for all your replies and time.
Ahh gotcha. I assumed you were in the US, my bad.
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