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MG jam?


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Previous discussions have highlighted the reliability of most WW2 MGs. Jams were relatively rare, jams that couldn't be cleared during the normal barrel switching, belt changing operation of the weapon doubly so. There are accounts of entire Battalions of machine guns firing for hours without a break not suffering any unscheduled stoppages.

My experience with CMx1 was that stoppages were too frequent, and "permanent jams" much too frequent.

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If you fire a lot of rounds with an MG, especially the WW2 variety, the barrels heat up quite a bit, and could be damaged. Some of the early 30 cal MGs the US used in both the European and Pacific theaters were water cooled, meaning the crew had to carry around cans of water to attach to the barrel to keep it cool. Those barrels were not the type that could be changed out.

My personal experiences include the M-60 MG that was used during the Vietnam War. I have seen barrels glow cherry red when lots of rounds were fired through them. Barrel changing was fairly easy, as long as someone was carrying a spare around. In most cases we did not bring spare barrels along, but took our chances that we did not damage the barrel. It becomes a matter of shedding weight vs. the chance that a barrel could be damaged from overuse.

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Question on real life barrel changes.

What is the main reason for changing a barrel? heat or worn out? or some combination?

Excessive heat, which if left unchecked can cause the barrel to warp in a hurry. That's why MG42 gunners carried spare barrels, for instance.

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MG42 barrel swapping wasn't occasional, it happened every couple minutes! blame the murderously hight ROF. I recall a reading somewhere that .50 Browning should be allowed to cool down after about 40 rounds(?) continuous fire. In 2012 the Army was touting their new M2A1 .50 cal with quick-change barrel as the best thing since sliced bread.

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MG42 barrel swapping wasn't occasional, it happened every couple minutes! blame the murderously hight ROF. I recall a reading somewhere that .50 Browning should be allowed to cool down after about 40 rounds(?) continuous fire. In 2012 the Army was touting their new M2A1 .50 cal with quick-change barrel as the best thing since sliced bread.

Off the top of my head, anything above 40 rounds per minute is considered rapid fire for the M2HB and leads to heat building up in the weapon. Three minutes of rapid fire is considered a "hot" gun and more than five minutes at rapid fire means you have a risk of rounds cooking off. Between 15-40 would be considered slow fire but even that wouldn't allow the gun to cool, just prevent it from building up more heat. The 50cal is somewhat exceptional in that regard though.

Other machine guns are more tolerant and can employ more aggressive firing rates without concern, due to the quick-change barrels, smaller rounds, etc.

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Heat. "Worn out" takes thousands and thousands of rounds delivered downrange, not something you're going to see in a typical firefight.

I had an M-60 MG squad in my weapons section in the Marines. My gunners would change barrels about every 1,000 rounds or less depending on the rate and duration of fire. If the barrel got hot enough, it could actually droop until you were shooting into the ground. One gun would change it's barrel and the other would pick up it's rate of fire to cover the lack of fire from the gun that was out of commission until it was back up (no more than 15 to 20 seconds). Each gun had a "T&E (traverse & elevation) bag" with a barrel change and an asbestos glove. My 60mm mortar crews would usually try to steal the gloves so they could fire the tubes with just the baseplate attached and not have to set up tripods. Much quicker to get. Rounds down range. :D

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