Indianapolis Ordnance Sten Issue

[Brit plumber]

Trivial bit of info but I find interesting non the less, the Mauser Bk27 cannon, when operating at its natural speed, the return spring never actually extends, the gun cycles quicker than the springs can extend. Only on the last shot can the springs fully return to rest. The gun is actually electrically delayed to slow the rate of fire it’s that quick. Oh and barrels barely last 2000 rounds before they are smooth bored by ware.

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[Lee Enfield]

Trivial bit of info but I find interesting non the less, the Mauser Bk27 cannon, when operating at its natural speed, the return spring never actually extends, the gun cycles quicker than the springs can extend. Only on the last shot can the springs fully return to rest. The gun is actually electrically delayed to slow the rate of fire it’s that quick. Oh and barrels barely last 2000 rounds before they are smooth bored by ware.

That's also why MG42/MG3 require the anti bounce weight in the bolt carrier.
The bolt locks at the moment of firing, but in the instant of ignition, the rollers and lock piece may have inertia "bounced" into a semi unlocked position, creating an out of battery or unlocked firing situation.