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M1A Accuracy Issues: How to Unitize an M-14 Gas System

by Gus Norcross   |  September 21st, 2012 9

When an M-14 type rifle is optimized for accuracy, the stock fit will be adjusted (possibly bedded) for consistent downward tension on the front band and the handguard will not touch the stock. This barrel tension is critical to match grade accuracy. Unlike bolt guns, M-14s do not shoot well with free floated barrels.

Why? No idea. To paraphrase Dr. McCoy from the original Star Trek TV show, “Dammit Jim, I’m just a simple country gunsmith, not an engineer.” It works. Trust me.

The front band is sandwiched between the gas cylinder and the barrel shoulder, and it will move around a bit on a standard rifle, creating inconsistent barrel tension. Many years ago, military rifle teams developed methods of “unitizing” the gas system and front band. This means the front band is attached solidly to the gas cylinder resulting in the same barrel tension shot after shot. There are two common methods of unitizing: welding, or drill and tap.

Welding the band to the cylinder must be done carefully to avoid creating tight spots in the cylinder bore. The USMC attached front bands to the rear gas cylinder mounting ring with three small TIG welds. The cylinders from Quantico were so cleanly done on the inside of the ring that the welds could not be seen when the rifle was assembled. On some commercially welded assemblies, the front band is welded directly to the cylinder with a heavy bead risking distortion of the cylinder bore.

I am not a welder and don’t pretend to be one, so I use the old AMU/NGMTU “screw and glue” method of unitizing. The front band, gas cylinder and spindle valve are assembled in a fixture, and two holes are drilled through through all three parts. Spindle valves are very hard and must be annealed before drilling. The parts are then removed from the fixture, and the holes in the front band and cylinder are clearance drilled slightly larger so 6-32 machine screws will pass through them. The holes in the spindle valve are tapped and the band is countersunk so the flat head screws will seat flush. The screws are permanently epoxied in place during assembly. Correctly done, this should result in a permanent assembly with no cylinder bore distortion.

  • Jeff

    My little M1A 16" Socom shoots 3" at 300 yards consistently! Never fails, never had a jam or anything. I love it!!!

  • M-14parts.com

    What is usually not taken into account when unitizing is that fact that it cannot be done in isolation with reliable results. The unitized front band location must be specific to the rifle and stock ferrule for which it is being unitized. The front band must be centered on the stock ferrule in order to consistently return to the same location after each shot. Returning to the same location after each shot is what creates consistency from shot to shot in the M14 type rifle.

    Many proponents of unitizing in isolation leave out this critical consideration. The most reliable way to unitize is by welding the face of the lower portion of the front band to the gas cylinder after bedding and while the action is in the stock.

    To do this, the front band should be left loose by backing off the gas lock 1/4 turn and then placing the action into the stock and securing the receiver with either the lug screws or trigger assembly. If the rifle was bedded properly, there will be some front band tension that has the result of pre-loading the barrel. This tension forces the front band to center itself on the stock ferrule.

    If there is no band tension that pre-loads the barrel, you must apply artificial tension by placing a large enough wire inside the stock channel so that the bottom of the gas cylinder is forced upwards when the action is place in the stock. Then one can use the method outlined above to find the center position for the front band on their particular rifle.

    Once you have determined it is centered, you then secure it by tightening the gas lock. This is when you make a small weld on the lower portion of the front band, where it is generally secured by the gas cylinder lip. (On later gas cylinders only) This small weld will hold the front band in the proper position, and it can then be removed for additional welds or the method of your choice.

    If you plan on using the AMU method, or the USMC, you cannot do it while the gas cylinder is installed, and thus are forced to use some method of indicating your center. Because the process for both requires the gas cylinder be removed from the rifle, getting a perfectly centered front band and stock ferrule relationship is more difficult. Even if a good indicator is used to mark the location of the front band, maintaining that location during the process is less than ideal.

    What's more, if a gas cylinder is unitized in complete isolation, by use of a jig or some other method that doesn't take into account the rifle it will be used on, there's only a slim to none chance it will fit any random your rifle. Pre-unitized gas cylinders that don't create a near centered relationship between the front band and stock ferrule, are often worse than loose front bands.

    Unitizing in isolation ranks right up there with specialized gas pistons, solid op rod spring guides and other components that are not rifle specific in terms of their relationship to the rifle in which they are used.

    The bottom line is that if you are going to unitize your gas cylinder with the front band, it needs to be done based upon the relationship between your front band and stock ferrule. Otherwise it's like sticking a square peg in a round hole.

    • Gus

      BS I'd hate to tell you how many trophies have been won using the above method. If the barrel is centered in the stock and the front band is centered on the gas cylinder by the drilling fixture there won't be a problem.

      • M-14parts.com

        "If the barrel is centered in the stock and the front band on the gas cylinder by the drilling fixture there won't be a problem" is the crux of the issue and pre unitizing does not take into account the various tolerances held by today's commercial receivers, barrels, and stocks. Sure, if we had perfect real M14 receivers, and control over all of the various barrels and stocks used in today's commercial environment, pre unitizing gas cylinders before bedding might be a feasible alternative, but that's simply not the case in today's environment. If you pre unitize a perfect gas cylinder and the top barrel spline is not top dead center and you bed the weapon based on the stock ferrule and front band, the receiver will be sitting cock-eyed in the stock. It's that simple.

        We build trophy rifles too, but we are forced to use the commercial components available on the market in today's environment, we don't have the luxury of using tax dollars and near perfect components.

        The AMU method is an excellent technical method for securing the front band to the gas cylinder, as is the USMC method, but it can't be done in isolation with reliable results.

    • Fred

      I'm with Gus on this…..I mean what does the NGMTU know…….

      • Fred

        Or the AMU

      • Fred

        Or the USMC….

  • CWO John M. Miller

    Folks, Gus is correct, if the bedding collar is used on the barrel during receiver bedding, the barrel will be
    centered in the stock. Then by using care to insure the band os perfectly centered on the gas cylinder (by
    the fixture used for drilling / welding ) the pressure on the stock will be uniform. This will allow the barrel
    harmonics to be the same from shot to shot. Another quick method would be to place a thin washer between
    the barrel shoulder and the back of the band to crush up when the lock is tightened upon assembly. CWO
    Bruce Woodford developed these washers to insure the "unitized" bands had support, and to help prevent
    the bond (screw or weld) from breaking. They do work nicely to solidify the floppy band on a "field gun"
    As long as the lock stays tight the band / gas cylinder doesn't move. We have used the screw in method
    for years, and have had no trouble (if care in assembly is followed) CWO John M. Miller (U.S. ARMY RET)

  • sheaboy

    i have a m1a super match krieger barrel mcmillian stock i have recently had some issues getting my riffle to stay zeroed it will shoot the same hole at 150yards then i set it down for a min pick it back up and its moved zero sometimes a couple inches sometimes a foot do you think this is my problem or would it be a scope or mount issue i have the steel springfield scope mount installed by springfield and a leupold vx3 scope

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