Page 1 of 2 12 LastLast
Results 1 to 10 of 13

Thread: Midlength and Carbine Length Question...

  1. #1
    Join Date
    Dec 2006
    Location
    SouthEastern U.S.
    Posts
    1,810
    Feedback Score
    0

    Midlength and Carbine Length Question...

    I've noticed that there are carbine length AR's (like my 16" Colt 6920's), and then there are Mid Length AR's, which are also 16" bbl guns.
    I would like to know WHY 16" carbine length guns are even made, IF the mid length gas system is considered to be more reliable????
    Why wouldn't all 16" guns just be made into mid length system rifles??
    Is there ANY difference between the two 16" rifles, other than the length of the gas tube, and the point the FSB is installed on the bbl??
    Is the position of the FSB, and the length of the gas tube the ONLY difference between the two rifles???
    Just curious and trying to learn something here, and also trying to decide on my next purchase/build, as I only own carbine length rifles at this time...

    Finally, can a 16" carbine length rifle, be made into a mid length rifle, with the addition of a longer gas tube, and also the moving of the FSB out towards the muzzle, by a couple of inches??? (there is about a 2" difference in gas tube length between the two, correct???)

  2. #2
    Join Date
    Jul 2006
    Location
    Northwest IN
    Posts
    3,119
    Feedback Score
    2 (100%)
    You are correct in assuming almost all of that.

    You cannot easily convert to a midlength and wouldn't want to. That gasport would have to be filled and a new one drilled 2" forward.

    The carbine system has been around for a long time. They still produce them because there isn't anything really wrong with them and there are TONS of parts for them.

  3. #3
    Join Date
    Dec 2006
    Location
    SouthEastern U.S.
    Posts
    1,810
    Feedback Score
    0
    Ahh yes, did not think about the gas port hole needing to be moved in the bbl...
    Just would have thought Colt would have been primarily supplying mid lengths to the military if they were more reliable. After all, isn't that what the soldiers need? Guess it's not THAT much more reliable eh?

  4. #4
    Join Date
    Jul 2006
    Location
    Northwest IN
    Posts
    3,119
    Feedback Score
    2 (100%)
    More reliable in the sense that certain parts might last a little longer but those parts are usually replaced at that level at the correct intervals to avoid problems.

    Midlengths aren't more reliable shot to shot- just after half a dozen cases of ammo you may get to squeeze another case out before you need to replace something.

    I don't have accurate numbers- I never cared. I just liked the Midlength because it's proportions were closer to the 20" rifle as opposed to have 7" of handguard and 9" of FSB and barrel. Not so handsome if you ask me.

  5. #5
    Join Date
    Aug 2006
    Location
    Texas
    Posts
    205
    Feedback Score
    0
    Quote Originally Posted by Paul Cataldo View Post
    I've noticed that there are carbine length AR's (like my 16" Colt 6920's), and then there are Mid Length AR's, which are also 16" bbl guns.
    I would like to know WHY 16" carbine length guns are even made, IF the mid length gas system is considered to be more reliable????
    Because the carbine length is what the military made. It was the shortest the gas system could be made and still be reliable. ArmaLite (not the original one) was the first to design and made midlength gas system rifles.

    Why wouldn't all 16" guns just be made into mid length system rifles??
    Because Colt didn't design it nor the military request or adopt it.

    Is there ANY difference between the two 16" rifles, other than the length of the gas tube, and the point the FSB is installed on the bbl??
    No. Well, longer handguards.

    Is the position of the FSB, and the length of the gas tube the ONLY difference between the two rifles???
    Yes, and the longer handguards.

    Just curious and trying to learn something here, and also trying to decide on my next purchase/build, as I only own carbine length rifles at this time...

    Finally, can a 16" carbine length rifle, be made into a mid length rifle, with the addition of a longer gas tube, and also the moving of the FSB out towards the muzzle, by a couple of inches??? (there is about a 2" difference in gas tube length between the two, correct???)
    There is 2" of difference, but I wouldn't know why you'd want to do that. It's easier to swap a barrel assembly out than to close up and redrill gas ports and move FSBs.

    The main benefits of midlength gas system rifles (IMHO):

    1) more handguard length, less exposed barrel
    2) longer sight radius
    3) easier to put a bayonet on

    Another benefit that people claim is that recoil is softer. I personally can't tell the difference. Yet another is longer dwell time before extracting the cases resulting in a lower potential of stuck cases (something that plagues shorter guns more than longer guns), but if you're using good ammo and you've got a NATO dimensioned chamber, you shouldn't have this problem.
    Nemo me impune lacessit

  6. #6
    Join Date
    Aug 2006
    Location
    Colorado
    Posts
    823
    Feedback Score
    0
    Quote Originally Posted by SuicideHz View Post
    More reliable in the sense that certain parts might last a little longer but those parts are usually replaced at that level at the correct intervals to avoid problems.

    Midlengths aren't more reliable shot to shot- just after half a dozen cases of ammo you may get to squeeze another case out before you need to replace something.

    I don't have accurate numbers- I never cared. I just liked the Midlength because it's proportions were closer to the 20" rifle as opposed to have 7" of handguard and 9" of FSB and barrel. Not so handsome if you ask me.
    +1 on liking the midlength unit. I'm 6'1" and I reach right out to the end of the hand guards.

    The extra 2 - 3 inches on the sight radius is gravy and I understand the further the gas ports are from the chamber the lower the pressure placed on the BCG.

    Mine is a RRA with heavy bbl that runs the full length. I recoils different than the shorter gas system carbines, I think the extra weight keeps the muzzle down. It seems to push straight back.

    Lastly here's one of those vague answers; "I just like the way it feels and shoots."

  7. #7
    Join Date
    Jun 2006
    Location
    USA
    Posts
    305
    Feedback Score
    1 (100%)
    After you pull the trigger
    Gas Port Pressure v. Barrel Length Curve?
    Armalite Technical Note 48, The Effects of Barrel Design and Heat on Reliability

    I believe that most commercial ARs are based upon the US Military M4/M16 variants, cosmetically if not to spec. 16 inches is the legal minimum for rifle barrels (without registering a SBR), so one might determine that M4-look commercial ARs use the carbine-length gas system because the M4 uses it, not necessarily because it is an optimum design. Since Colt's primary market is military, and since non-military customers often want something as close to MIL-SPEC as they can get, it's understandable that they might not offer a mid-length gas system. Armalite, RRA, and others, however, have seen fit to offer what may be technically a superior gas-system configuration for the 16" barrels. There are mid-length precision barrels available from multiple sources. Unfortunately the choices are more limited for chrome-lined barrels.

    I'm curious to know if the carbine-length gas system is really optimal for the M4-length 14.5" barrels. IIRC, the 14.5" Noveske barrel is a middie, and I imagine that others offer a similar configuration.
    Aubrey<><

  8. #8
    Join Date
    Aug 2006
    Posts
    287
    Feedback Score
    0
    +1 What they said.

    I also like the way mine feels and shoots.

    Mine is a limited production Rock Creek chrome lined with M4 feedramps, medium contour barrel which I replaced my HBAR carbine gas system barrel of my 6721 carbine.

    I also have a LMT 16" M4 CAR and I prefer to shoot my mid length carbine if I had a choice between the two.

    Since you already have a carbine gas system I would suggest trying a mid length for your next one, most guys like it and I've only heard a very few that didn't like them or don't notice any difference.
    YMMV

    AR-15 SP1 owner since 1971
    NRA and CRPA life member

  9. #9
    Join Date
    Aug 2006
    Location
    Texas
    Posts
    205
    Feedback Score
    0
    In my armorer's class, I was taught that the carbine length gas system was set because it was the shortest they could go reliably.

    The 16" barrel midlength gas system is a product of the shortest civ legal barrel (without SBR paperwork), where there's enough barrel forward of the gas port to reliably cycle the gun.
    Nemo me impune lacessit

  10. #10
    Join Date
    Jun 2006
    Location
    NoVA
    Posts
    10,780
    Feedback Score
    17 (100%)
    The carbine length gas system has been around since the Colt XM-177 in the mid 1960s.

    It is my belief that since the carbine length gas system worked well on the short barreled XM-177s Colt probably didn't want to reinvent their own wheel and just used the carbine length system in the XM4 (in the 1980s) then later in the M4 and M4A1. The weaknesses of the carbine length gas system probably weren't realized until the M4s adoption when it was subjected to really heavy full-auto use by Ranger units etc.

    The USMC never wanted the M4 to be a replacement for an M16A2. The M4 was just going to be the next carbine (used like the M1,M2 and M3 carbines had been) which is to be issued to commissioned officers, staff NCOs, tankers, MPs and others who would be typically only issued pistols. It was meant to give more power and range than a pistol and smaller and easier to carry around vs a full sized rifle. The original XM4 (A2 type upper) had 85% parts is common to the M16A2.

    Whenever you have a choice in a 16" barrel the mid-length should be the 1st choice.
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •