 This is an M60 tank and the machine gun firing is the 7.62 millimeter M73. This machine gun is used primarily on tanks and is coaxially mounted with the main gun. The M73 machine gun is a lightweight, air-cooled weapon. It is recoil operated with a gas assist and is completely automatic. The M73 has a quick change barrel, just swing down the receiver far enough to expose the chamber and wearing a protective asbestos glove, pull out the hot barrel. The new barrel is just as easy to insert. It has a fixed head space which requires no adjustment. Swing back the receiver, lock in place and start to load. The M73 machine gun weighs 28 pounds and is 34 and 3 quarter inches long from the flash hider to the back plate of the receiver. The muzzle velocity is approximately 2800 feet per second. The chamber pressure, 50,000 pounds per square inch and it has a maximum range of 3,750 meters. Its cyclic rate of fire is between 450 and 500 rounds per minute and it is fed from a disintegrating metallic link belt from either the left or right side. The M73 fires the standard 7.62 millimeter NATO cartridge slightly shorter and lighter than the caliber 30 cartridge. This weapon fires three types of ammunition, ball, armor piercing and tracer, linked for field use in a ratio of 4 ball or armor piercing to one tracer. The M73 machine gun is mounted to the left of the main gun mount of the M60 tank by a clamp which is fastened to the mount by two allen head screws. The only other connection is the cable to the tank's electrical system used to operate the solenoid which fires the gun. To clear the weapon before handling it for any purpose, push forward on the cover latch rod, raise the cover and the feed tray, then pull the charging handle to the rear. Set the safety on safe. Check to make sure no round is left in the chamber. Then place the safety on fire. Press the trigger, allowing the barrel extension to move forward. You are now ready to load the weapon. First lower the feed tray. Then charge the weapon by pulling the charging handle to the rear. Set the safety on safe. Make sure the open side of the link faces down and place the ammunition belt in the feedway. Close the cover to prevent the belt from falling out of the feedway. Set the safety on fire and the gun is ready to fire. This weapon fires from the open bolt position. Since the M73 is coaxially mounted with the main gun, it has no sights of its own. If adjustments are to be made, they must be done by bore siding with the main gun. The M73 can be fired electrically from the gunner's position or the tank commander's position. The gun can also be fired manually by pressing the trigger on the back plate of the receiver. The gun continues to fire as long as the trigger is depressed. While the M73 is fully automatic, it can be fired in single shots or short bursts. If the manual trigger or the electrical trigger is fully released after each burst. To unload, follow the same procedure used to clear the weapon. Remove the ammunition belt from the feed tray. Charge the weapon if the barrel extension is forward. Set the safety on safe. Check the barrel to see if it is clear. Put the safety on fire and allow the barrel extension to move forward. To prevent overheating, to extend the life of the gun and maintain its accuracy, the barrel should be changed frequently. To change the barrel, pull back one of the two disconnector grips on the receiver assembly. Rotate the receiver, allowing it to swing down, then withdraw the barrel from the mounting block assembly. Insert the spare barrel and check the barrel locator on top of the mounting block. The locator should be flush with the top. Turn the receiver back to its original position, checking the disconnector grips to see that they are firmly engaged and the barrel change is completed. Now firing may be resumed. For general disassembly, the M73 is separated into six main groups. The first of these is the cover group, consisting of the cover and feed tray. Number two is the backplate group. This includes the driving springs and guide rods and the backplate. Number three is the barrel extension group, consisting of the barrel extension and the breech block. Number four is the charger assembly. Number five is the barrel and mounting block group. Here we have the barrel, the barrel jacket, the flash hider, and the mounting block. And number six is the receiver group. Now let us see how the M73 machine gun is actually disassembled into its six component groups. Here again, first clear the weapon. Disassembly begins with the removal of the cover group. Push the cover latch rods forward and remove the cover. Remove the feed tray. Set the parts down in this left to right sequence. It will avoid confusion and make the assembly procedure easier to accomplish. Next, remove the backplate. Before you do this, make sure the recoiling parts are in the battery position. Press the trigger to allow the barrel extension to move forward. This safety measure releases the tension from the guide rods and driving springs. Then push the guide rods forward. Open them 45 degrees counterclockwise to unseat the guide rods and driving springs. Remove both guide rods and driving springs. Lift the backplate straight up and slide it off the receiver rails. Next, retract the barrel extension but do not use your fingers. The rammer can cause serious injury as it snaps back. Pull the charger handle to bring the barrel and barrel extension back. Press the buffer support lever and pull rearward on the barrel extension. Support the barrel so that it will not drop down when it is disconnected. Separate the barrel from the barrel extension. Remove the breech block assembly by sliding it to the left and then lifting it straight up. To separate the charger assembly from the receiver, first take off the retaining ring from the charger mounting stud. Slip the charger off the rear mounting stud and remove it from the front buffer support pin by sliding it to the rear. To remove the mounting block, pull back the right or left disconnector. Rotate the barrel jacket and push it forward. This leaves only the receiver group. This completes the disassembly of the machine gun. Remember to set the parts down in this sequence in the order of their removal. To assemble the weapon, reverse the disassembly procedure. Replace the mounting block on the receiver. Set one of the disconnectors in the hole on the mounting block. Pull back the other disconnector. Rotate the mounting block into position and release the disconnector. Next, the charger. This assembly is so designed that with but a minor change it can be mounted on either the right or left side of the receiver. To make this change, slide the connector to the opposite side by depressing the plunger and the spring. Mount the charger assembly by setting the forked front section on the buffer support pin with the connector in the slot on the receiver. Slide the rear of the charger on the mounting stud. Replace the retaining ring. To replace the breach block on the barrel extension, line up the two lugs on the front side of the breach block with a dismount notch on the left side of the barrel extension. With a striker of the firing pin forward, drop the breach block in place and slide it to the right. Set the barrel on the barrel extension and replace them in the receiver, making sure that the locator slot faces up. The receiver rails must engage the grooves on the barrel extension. Push the breach block to the extreme right so that it engages the rail on the receiver. Now slide the barrel and barrel extension forward. When you pull back the action lever, be sure to keep your fingers out of the way of the rammer. The action roller is aligned with a closing cam on the bottom right side of the receiver. The locator slot on the barrel is aligned with the locator. Depress the support lever, then push the barrel extension to battery position. The locator should now be flush. Now with a trigger up, align the grooves on the back plate with the rails on the back of the receiver and drop the back plate into position. Insert the driving springs and guide rods through the back plate into the barrel extension. Push forward and turn clockwise until they lock in place. Next, seat the feed tray. Make sure that the bullet ramp is to the front and that the brackets on the feed tray align with the latch rods on the receiver. Align the four cover brackets with the brackets on the latch rod assemblies. Push the cover down to the latched position. When you have completed the assembly of the machine gun, make a functional check of the weapon to make sure it operates properly. To change the feed from left to right, remove the cover and feed tray by pushing in the latch rods on the receiver. Lift the cover off and remove the feed tray. Adjust the feed tray by depressing the plunger and sliding the round stop to the left side of the tray where the plunger engages the locating hole. The feed tray is properly set when the L on the feed tray is adjacent to the L on the round stop. Place the feed tray. Now the cover is changed. First, move the feed retainer support to the left side. Slide the feed cam fully forward and remove it from the cover. Lift out the feed support. Remove the feed track and feed slide. Turn it end for end 180 degrees and replace it in the cover. This will align the L on the feed track with the L on the cover. Now slide the feed support retainer to the opposite side of the cover and replace the feed support. See that the L on the feed cam faces up. Replace the feed cam. See that the L on the feed cam lines up with the L on the cover. And slide it to the rear. Finally, slide the feed support retainer to the central locked position and replace the cover. This completes the feed direction change. You have seen the disassembly and assembly of this tank's coaxial mounted machine gun, the M73. Part two of this film will describe the cycle of functioning.