Timing nut . If the timing nut can bemoved with one finger or it doesn’tclick as you move it, its spring is weakand it won’t hold timing. Tell your ar-morer.

2. Pull the charging handle backuntil the barrel-locking spring lug isaligned with the 3/8-in hole on thereceiver’s right side. To keep the boltback, insert the small loop of an M2ammo link between the trunnion blockand barrel extension.

How to Headspace

Barrel and barrel extensionthreads. If the threads are chipped orburred, it will be difficult to screw inthe barrel. What’s worse, you may thinkyou’ve screwed in the barrel, but youhaven’t. Result: bad headspace. Yourarmorer can usually stone chips andburrs smooth.

Gauges bent, rusted, pitted?

Locking spring loose, weak or broken?

Burred or chipped threads?

iming and headspacing are every-thing when it comes to firing your M2machine gun. If you don’t headspaceand time your M2 every time beforeyou fire or after you change the barrel,a round can go off inside the gun. Thatcould injure you and damage the gun.

Pre-check ChecksIf your M2’s in bad shape now, you

won’t be able to headspace and time itlater. So before you go to the field, dothese checks:

Gauges. If the headspace and tim-ing gauges are bent, rusted or pitted,you can’t accurately gauge, so tell your

PS 575 45PS 575 44 OCT 00

M2 Machine Gun . . .

Barrel locking spring. If the springcan’t hold the barrel in place, the bar-rel can turn during firing and headspaceis lost. So test the spring by getting thecorrect headspace and then trying tounscrew the barrel. If the barrel turns,the spring is weak or loose. Tell yourarmorer.

armorer. He can order new gauges withNSN 5250-00-535-1217.

you've got a headspacing

problem!

hey, thAT'S

NOT VERY

NICE.

1. Raise cover completely.

3. Screw barrel all the way into barrelextension.

Test timing nut spring

Lug Hole

3. Press the trigger. If the gun doesn’tfire, go to the next step. If it does fire,you’ve got early timing.

If the GO end fits and the NO GOend doesn’t, the headspace is OK. Ifthe GO end still won’t fit, repeat theselast five steps until it does.

Do not unscrew the barrel more thanfive clicks beyond the first two clicksin steps 1–5. If you have to turn thebarrel more than seven clicks,something’s wrong. Tell your armorer.

Headspace Too LooseIf the NO GO end of the gauge fits

into the T-slot, the headspace is too

3. Ease the bolt forward.4. Pull back on the charging handleuntil the barrel extension and trunnionblock are about 1/16 inch apart..

2. Unscrew the barrel one click.

Headspace Too TightIf the GO end won’t fit, headspace

is too tight. Do this:1. Pull back the charging handle untilthe barrel-locking spring lug is cen-tered in the 3/8-in hole.

the extractor and try to insert the GO/NO GO gauge all the way up to thering into the T-slot between the boltface and rear of the barrel.

If the GO end goes down the T-slotto the center ring and the NO GO won’tgo in, headspace is OK.

6. Ease the bolt forward.7. Pull the charging handle back untilthe barrel extension and trunnion blockare no more than 1/16 inch apart.

Go No go

Repeat the five steps until the GOend fits, but the NO GO end doesn’t.

How to TimeAfter headspacing comes timing.

1. Pull the charging handle all the wayback and cock the weapon. Ease thebolt forward.2. Pull the bolt back far enough to in-sert the NO FIRE gauge between thebarrel extension and trunnion block.Insert the beveled edge of the timinggauge against the barrel notches.Slowly release the charging handle.

PS 575 47PS 575 46 OCT 00

loose. To fix loose headspace, do thesame five steps you did for too tightheadspace, except screw in the barrelone click.

4. Unscrew the barrel two clicks,remove the link and let the bolt goforward.

To see if the barrel is locked withthe bolt in the forward position, tryto turn the barrel in either direction. Ifit turns, something’s wrong. Tell yourarmorer.5. Pull charging handle back to cockweapon.

8. Keep the charging handle back tomaintain the 1/16-in separation. Raise

IT'S A BARREL OF

FUN!

5. Insert GO/NO GO gauge again.

Lug Hole

Screw in one click

7. After the gun fires, turn the nut tothe right two more clicks and stop.8. Take out the gauge and put on theback plate. Cock the gun, then ease thebolt forward.9. Recheck the timing two more timeswith the back plate on. If the timingstill isn’t right, do the early/late timingprocedure one more time.

Still no luck? Tell your armorer.Something’s wrong.

4. Pull the bolt back only far enoughto insert the FIRE gauge, and slowlyrelease the charging handle.

PS 575 49 OCT 00PS 575 48

4. Pull the bolt back just far enough totake out the NO FIRE gauge and putin the FIRE gauge with the bevelededge against the barrel notches. Slowlyrelease the charging handle.

5. Press the trigger. If the M2 fires,timing is OK. If it doesn’t fire, youhave late timing.

Early/Late TimingNever cock your M2 with the back

plate off. The driving spring rod couldgo through your chest. The bolt mustbe forward before you take off theback plate.1. Take the gauge out of the re-ceiver. Cock the M2, then ease the boltforward.2. Take off the back plate.3. Turn timing nut all the way downto the left.

6. Turn the timing adjustment nut oneclick to the right. Push up on the trig-ger bar. Continue to alternate turningthe timing adjustment nut one clickright and pushing up on the trigger baruntil the M2 fires.

Mobile Subscriber Equipment . . .

You must ground all three with separate ground wires and rods to avoid apossible shock. Not grounding the signal entry panel can create an additionalproblem: signal interference.

And while you’re at it, look at the terminals and ground lugs for dirt, grease,corrosion and paint. They can kill a good ground connection. Remove dirt andgrease with solvent, NSN 6850-00-281-1985. Use fine sandpaper or a wire brushto get rid of any corrosion or paint. But be careful using these abrasives. Youcould do more damage than you do good!

1. Generator: Run a ground wirefrom the ground terminal in the

terminal box to the trailer’s groundlug. Then run another ground wire

from the trailer’s ground lug toearth ground.

2. S-250 shelter’spower entry panel:

Ground the E1ground lug.

3. S-250 shelter’ssignal entry panel:

Ground the E1ground lug.

Here are the places to ground the LOS or

RAU...

5. Push up on trigger bar. Gunshouldn’t fire.

Armorers, if you have M2s inyour arms room, copy this articleand use it to train your M2 gun-ners. It will help protect your unitand your M2s.

f your mobile subscriber equipment (MSE) line-of-sight (LOS) radio termi-nal or radio access unit (RAU) is not grounded in three places, it’s not groundedsafely.