Barrel Coaxial

How did WW2 Air Cooled Machine guns stay cool when in some cases covered with a metal sleeve?

I know a lot of WW2 Tank's air cooled hull machine guns and some coaxial machine guns from various nations are exposed without a sleeve or guard. Some air cooled coaxial machine guns I noticed are semi recessed into the mantlet or turret and is the gap left around the diameter of the barrel to allow air to circulate around the barrel.lastly, do any countries during WW2 use fans and air vents to pump air around around air cooled coaxial machine guns. I suppose all of the above might not be necessary as I don't know how fast and how long it takes for a air cooled machine gun barrel to heat up and cool down. Cheers John.

Barrel heating varies from gun to gun. Rate of fire, how many rounds are fired over a given period of time, barrel thickness and the effeciency of the cooling jacket all come into play.

The German MG42 was the worst offender. A barrel change was REQUIRED after just 100 rounds of sustained fire. Tanks usually had heavy barrel versions of the MG34 though.

The American Browning M1919 didn't really have problems with barrel overheating. The ROF was relatively low and the barrel quite thick. If the gunner practiced good fire discipline (bursts only - sustained fire was pretty useless) it probably wasn't an issue.

The gun mountings were snug. Any hole in the armor is a weak point so these were kept as small as possible. I was crawling around an M8 armored car yesterday and the coax M1919 was in the mantlet so tight I wonder if they had to grease it to get it in there In many instances the gun was contained entirely within the vehicle with a small hole only large enough for the bullets to pass in the armor.

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