20th Installment – Semi Auto C5A1 Build – T-Slot Mods., Maintenance and Repairs
Tee-Slot Modifications, Maintenance and Repairs
For this modification its best to start with an Israeli 7.62mm modified breech bolt which has the Tee-Slot has already been remanufactured from the old .30 caliber, M2 ammunition to the 7.62mm NATO cartridge. These modifications were made to provide clearance for the rim of the 7.62mm NATO cartridge. If the Tee-Slot is left unmodified in .30 caliber, the rim of the 7.62mm NATO cartridge will hang up on the Tee-Slot thus causing a malfunction when fired.
For those of you who are purchasing the C1/C5A1 breech bolt instead of modifying an existing .30 caliber breech bolt. There are several issues that you may have to content with. The Breech Bolt face and Tee-slot of the M1919A4 .30 caliber Machinegun was modified to accept the 7.62mm NATO cartridge and M13 metallic links. As with the fielding of any new or redesigned weapon system problems sometimes crop up immediately or take years later to identify and the C1 is no different. It appears that during the remanufacturing process to the C1 configuration a number of the breech bolts were improperly manufactured. This appears to be a real problem as the guns were remanufactured in the late 1960’s and the problem was not identified until publishing of C-71-126-000-/CS-007 dated June 7, 1978. The quality control in the remanufacture process must have come into question.
This illustrates another possible problem for potential buyers of C1/C5A1 breech bolts can face, the buying of condemned breech bolts.
Some Breech Bolts were remanufactured with sharp leading edges which allowed the base of a cartridge to strike the sharp leading edges during initial charging of the gun, causing the cartridge case to become damaged and jammed in the upper portion of the Tee-Slot guide ribs. (See Detail A) If you should buy a breech bolt in this configuration it can be easily repaired to correct specification listed in Detail C attached.
Other Breech Bolts were remanufactured with the leading edges too long which will not correctly come into contact with the rim of the cartridge case which allowed excessive amounts of cartridges to fall through the gun instead pf the Tee-Slot, or causes misalignment and jamming of cartridges. (See Detail B attached) If you should purchase a breech bolt in this configuration you are going to have to microweld material to the leading edges. This job should be left to a professional welder. The breech bolt should be refinished to the configuration and specification found in Detail C attached.
Pictured in Detail C attached is the correct configuration of the C1/C5A1 breech bolt. The Tee-Slot grooves shall not exceed 0.058 inches in depth in the bushing area. The total depth if the Tee-Slot to the bolt face shall not exceed 0.126 inches.
To assist in determining a serviceable C1/C5A1 breech bolt the Tee-Slot rejection gauge was developed to assist the armorer. (See Figure 1). Attached is also information on the use of the Tee-Slot Rejection Gauge (See Figure 2)