The following are measurements taken of various Colt lightweight profile barrels. The above diagram (not to scale) is designed as a visual reference point. The actual drawing and Colt listed specs can be found on page 352 of the Black Rifle published by Collector Grade Publications, Inc.


The standard as established via Colt specs is:
A. .600
B. .575
C. .625
D. .625-.750

As you can see from the following information there is quite a bit of variances regarding Colt lightweight barrels.


Colt SP1 Carbine Ser # 9XXXX
A. .600
B. .590
C. .610
D. .650

Colt SP1 Carbine Ser #10XXXX
A. .610
B. .560
C. .625
D. .640

Colt SP1 Carbine Ser #11XXXX
A. .600
B. .560
C. .610
D. .640

Colt SP1 Carbine Ser#13XXXX
A. .591
B. .581
C. .633
D. .641

Colt SP1 Carbine Ser #14XXXX
A.      .600
B. .590
C. .630
D. .640

Colt SP1 Rifle Ser#3XXXX
A. .590
B. .580
C. .620
D. .635

Colt SP1 Rifle Ser #1XXXXX
A. .585
B. .571
C. .628
D. .640

Colt SP1 Rifle Ser# 2XXXXX
A. .612
B. .585
C. .625
D. .635

       Current production Colt 6520 A
A. .615
B. .575
C. .627
D. .633

Current production Colt 6520 B
A. .611
B. .571
C. .625
D. .638

       Current production Colt 6520 C
A. .605
B. .575
C. .626
D. .635

Colt XM177E2 Model 639 Ser# 47XXXXX
A. .605
B. .575
C. .626
D. .634

Colt XM177E2 Model 639 Ser # 479XXXX
A. .607
B. .572
C. .625
D. .633

Colt M16A1 Carbine Model 653 Ser # 929XXXX
A. .612
B. .571
C. .626
D. .638

Colt M16A1 Carbine Model 653 Ser # 927XXXX
A. .610
B. .572
C. .625
D. .631

Colt M16A1 Rifle Ser #925XXXX
A. .601
B. .571
C. .626
D. .632

Colt M16A1 Rifle ser #916XXXX
A. .600
B. .575
C. .627
D. .630

wow!  you realize your gonna be asked to post that like 4 times a week, right?  good info!

www.ar15.com/forums/topic.html?b=3&f=118&t=206532

Before anyone takes this as gospel, they need to read this first about the XM177E2 barrel profile.

Saw your post concerning the "Colt Stocks" and saw some questions on XM barrels. The first few original E2's were .562-.570 in front of the sight. Later barrels were changed to .612-.620 in front of the sight and this was standard specs for an XM177E2 for the rest of production.  I personally have Colt uppers which these dimensions are from, as well as from barrels checked at FT. Leonard Wood here in Missouri....

From a respected memeber on this board who wishes to remain unknown.

gospel…..just posting some info

I'm posting information on rifles and carbine I own or have access too...not reprinting info.

Scottryan read the damn information. Colt has a general specification for the M16A1 series(rifle and carbines)  if you read my post you’ll see that there are variations throughout production.  You seem to feel that Colt strictly adheres to their original specs……yet I’ve shown that 17 different rifles and carbines  had variations in the external diameter of the bbl at four locations.


Anyone that wants to post their barrel specs feel free to do so.

Quoted: gospel…..just posting some info I'm posting information on rifles and carbine I own or have access too...not reprinting info. Scottryan read the damn information. Colt has a general specification for the M16A1 series(rifle and carbines)  if you read my post you’ll see that there are variations throughout production.  You seem to feel that Colt strictly adheres to their original specs……yet I’ve shown that 17 different rifles and carbines  had variations in the external diameter of the bbl at four locations. Anyone that wants to post their barrel specs feel free to do so.

I never said they adhear to the original specs.  But you argue the fact that all XM177E2 barrels steps down to .570 when both you and I both posted a picture in the other thread that disputes this.

If you quit trying to argue with me on this and accept the fact that I am speaking the truth, I will quit posting.

Where have I said all XM177E2's are .570.......never said that...I said that was the spec Colt set forth.....as you can see from my chart they can be all over the place. The two XM177E2's I listed are closer to .570 then the .610 you listed, in fact the secret source you quote states” The first few original E2's were .562-.570 in front of the sight. Later barrels were changed to .612-.620 in front of the sight”

By the way thanks for insinuating that I’m making the #’s up. Guess I’ll have to post pics of the carbine and rifles I’m talking about…..oh wait you’ll still think I’m faking it or photo shopping the pics…….I can’t win with you….if you don’t agree with my information prove me wrong or shut the hell up……it's getting old..

Forget a Tag....I just coppied this whole page to my computer.

Great Job

Any chance you can get info for the other side of the front sight base too and possibly even get the location of each point from closed chamber out (left to right)?

Quoted: Where have I said all XM177E2's are .570.......never said that...I said that was the spec Colt set forth.....as you can see from my chart they can be all over the place. The two XM177E2's I listed are closer to .570 then the .610 you listed, in fact the secret source you quote states” The first few original E2's were .562-.570 in front of the sight. Later barrels were changed to .612-.620 in front of the sight” By the way thanks for insinuating that I’m making the #’s up. Guess I’ll have to post pics of the carbine and rifles I’m talking about…..oh wait you’ll still think I’m faking it or photo shopping the pics…….I can’t win with you….if you don’t agree with my information prove me wrong or shut the hell up……it's getting old..

I have proved you wrong pictures in the other thread.  You can clearly see when you compare the two barrels that the real XM177E2 barrel has less of a step down.  Why don't you post a picture of an XM177E2 barrel that shows a diameter of .570 in front of the front sight?

And your arrogant and snobbish attitude is not going to win any arguement.  You keep saying prove me wrong and "what do you know, I am a Colt expert" but you haven't posted any proof that contradicts my arguement.

Quoted: in fact the secret source you quote states” The first few original E2's were .562-.570 in front of the sight. Later barrels were changed to .612-.620 in front of the sight”

Key word there is first few

And you are not being very clever by leaving out the part that the .610 diameter is was the spec and most XM177E2 barrels had this diameter.

And what is your source for your info?