M2 Caliber .50 BMG Headspace
Warning: The following information is provide for reference use only. Proper Training as well as the appropriate Technical Manuals are required to operate this or any weapon system that you are unfamiliar with. Gun Safety is you responsibility. Note: Due to the maximum range of this weapon special safeguards and control measures need to be planned and applied. Max Range = 7,440 YARDS = 2.35 Miles or 6,765 METERS = 6.75 Km!
Headspace is the distance between the face of the bolt and the base of the cartridge case, fully seated in the chamber. Check and set headspace before firing, after assembling the gun, and after replacing barrel or receiver group.
Note: The barrel should be cleaned before it is installed.
Step 2. With the retracting slide handle, retract the bolt until the barrel locking-spring lug is centered in the 3/8-inch hole on the right side of the receiver.
Step 3. Hold the bolt in this position and screw the barrel fully into the
Note: At this point, check the barrel for rotation. Attempt to turn the barrel in either direction. Barrel should not turn. If the barrel does turn, stop here and check barrel notches and barrel-locking spring for damage.
Step 6. Holding the retracting slide handle, release the bolt, and slowly return the bolt forward. Do not press the trigger -- or let the bolt slam forward.
Step 7. Retract the retracting slide handle and separate the barrel extension from the
trunnion block by a 1/16-1nch gap,
Step 8. Raise the extractor out of the way so you can see better and try both ends of the go no go gage as shown below,
Note: Insert the go end of the gage between the face of the bolt and the end of the barrel, all the way up to the ring.
Step 9. If the go end of the gage enters the t-slot to the center ring of the gage, and
the no go end will not enter, headspace is correct. Remove gage. Headspace setting is now
Step 10. Retract the bolt so you can see the barrel-locking-lug spring in the center of
the receiver hole on the right side of the receiver.
Step 11. Unscrew the barrel one notch (click).
Step 13. Recheck headspace (step 9).
Step 14. Repeat steps 10 through 13 until the go gage fits but the no go gage does not fit.
Note: you should not have to unscrew the barrel more than a total of five notches (clicks) beyond the first setting of two clicks. If this condition does occur, turn in the machine gun to your unit armorer for inspection.
Step 15. If the no go end of the gage enters the t-slot, headspace is too loose. Adjust it using the same procedures as above, screwing the barrel into the barrel extension rather than out.
Step 16. Repeat steps 10 through 13, one click at a time, until the
no go gage does not fit but the go gage does fit.
USING FIELD EXPEDIENT METHODS
When a GO/NO GO gage is not available, you can still set the headspace and timing, using field expedient methods.
To Set Headspace:
Hold the bolt in this position and screw the barrel fully into the barrel
extension, then unscrew the barrel two clicks or notches.
Note: Due to the maximum range of this weapon special safeguards
and control measures need to be planned and applied. Max Range = 7,440
YARDS = 2.35 Miles or 6,765 METERS = 6.75 Km!
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