Installation and Performance Information the Guiette Manufacturing, Inc. M2HB .50 Cal. Blank-fire Conversion Kit The installation of a GMI .50 Cal. Blank-Fire Conversion Kit will enable a U.S. M2 (Browning) heavy-barrel .50 Caliber (12.7 x 99) machine gun to function with the following blank ammunition: U.S.G.I. M1 .50 caliber blanks (roll crimped with cardboard wad). U.S.G.I. M1A1 .50 caliber blanks (star crimped with no wad). Swanson's Motion Picture .50 caliber blanks (star-crimped with no wad). Foreign military blanks which are of the same design and overall length as the above. No permanent modification of the gun is required. To install: 1. Pull locking stud back and remove (unscrew) live-fire barrel support. This can be accomplished by placing gun on M3 tripod and using the GMI barrel support wrench, or in an emergency, a 4-ft. length of 3/4 inch bar stock inserted through 2 holes. Tag with gun serial number and shim number (1 thru 12). Leave shim on gun. 2. Install (screw-on ) blank-fire barrel support. Should hand-tighten to within 10-15 degrees of alignment, with setscrew hole on bottom. Wrench tightening should require a moderate effort to align. If necessary, remove original shim (wire-attach to live-fire barrel support) install shim furnished by GMI, and try again. If fit is still incorrect, you can either send shim back to GMI for replacement, or grind to correct thickness. Each ascending shim number represents an increase of .0025 inch, or 18 degrees of rotation (.050 inch per full turn of barrel support). After correct alignment is attained, be sure to engage locking stud. 3. Install blank-fire rear barrel assembly, headspacing in same manner as for live-fire barrel. 7/8 inch wrench flats are provided on piston. 4. Install (screw in) blank-fire front barrel assembly into blank-fire barrel support. Tighten until setscrew holes are lined up, and install setscrew. 5. Remove front cartridge stop and install blank-fire feedway adapter. It installs for either left hand or right hand feed as desired. It is a good idea to then wire the front stop to the live-fire barrel support to prevent loss. The conversion kit is designed to function with motion picture blanks, which are considerably more powerful (higher pressure) than U.S.G.I. or equivalent military blanks. In order to function with the latter, the front barrel muzzle is threaded to accept a 5/8-18 x 1-1/2 inch setscrew with a drilled restricting orifice. If requested, GMI will furnish three restrictor plugs in a variety of orifice sizes, one of which should work for either U.S.G.I. M1 or M1A1 blanks (specify). Since the recoiling parts with conversion kit installed weigh less than the live-fire parts, the rate of fire with blanks will be higher, probably in the 600-700 rpm range. However, do not use a barrel buffer with oil in it. The barrel buffer must be dry. Any adjustment of the rate of fire of the blank-fire conversion must be achieved by changing the restrictor orifice diameter (at the muzzle). All other operational characteristics of the gun are unchanged. If you have more than one gun: The conversion kit barrel support is matched, by assembly number, to the front barrel assembly. These parts are not interchangeable between conversion kits. You should keep a record of each gun by serial number, conversion kit assembly number, shim number, etc.. Conversion Kit Barrel Support Threaded Front, Wrench flats on piston, threads on rear of front barrel, setscrew and setscrew hole. Threads at muzzle of front barrel. Feedway adapter in place (shown for left-hand feed) Click here to return to the on-line catalog.