Indianapolis Ordnance Sten Issue

[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.

[browningautorifle]

Even the AR family uses a heavy buffer for some applications to make certain the bolt has locked and not partially unlocked at firing.

[Brit plumber]

The Mauser doesn’t suffer in that respect, when the round is fired it is physically locked with no way to unlock until the breech cylinder has moved rearwards. At this time the return springs are still compressed but not under compression. It’s a hell of a system and complicated yet simple. The only springs in use after the first shot is a firing contact spring the size of a Bic Niro spring and a kind of leaf spring to move the cam lever. It’s the momentum which keeps it running, genius.