For which 37mm, friend? Hand-crank, automatic, semi-auto, grenade launcher, air cannon, anti-tank, torpedo-boat gun?
The old Maxim 1-pdr was a 37mm, the French and the Yanks used a different 37mm in the First War and the family has grown from there.
Plastic, brass, aluminum, steel? Very short, short, medium, long, very long, super-long indeed?
The more specific you can be, the quicker somebody might say that they can help.
Good luck.
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