For the M3 you can use IXMOO ie all brass concentric no velvet trap instead opens and shuts by keyway on back plate latch as you lock and unlock baseplate.
About 5 GBP (7 USD) if you shop around. Probably cost that to post you one from here.
But you need the original spool as well.
And need to avoid the Barnack only FILCA.
I've forgotten if the F3 has a concentric option I use velvet plastic ones in cameras which don't take concentrics.
They stopped the bounce apart cassettes only
Lucky and Fotokemia still used the non crimp machines.
To clarify, the Leica cassettes come in two varieties -- the Barnack FILCA he refers to has a black knob on the end, which the key in the camera turns to open the gate when you put the film can in the camera. These black knob film cassettes will ONLY work in screw-mount (Barnack) Leica cameras.
When they produced the M-series of cameras, Leica introduced a film cassette with a chrome knob -- it is silver-colored, very distinctive. These cassettes will work in both M and Screw-mount cameras.
Loading the Leica cassettes can be a bit tricky -- some, but not all, bulk film loaders have a key to close the film gate after you wind on the film -- it's a plastic knob opposite from the film wind crank that you turn to close the gate. A Weston loader does this. Others may or may not. If you don't have one of those, you have to wind the film onto the spool manually, which is a bit of a pain.
But Leica cassettes, because they use a gate that the camera opens and closes, not felt, are guaranteed to never scratch.
Nikon made its own version of a Leica cassette, which also opens when you put it in the camera and turn the baseplate key. I have never seen one, but imagine it works the same. They don't seem to come up for sale often and would be hard to find. Leica cassettes are much more common.
Having said all that -- I regularly use standard metal reloadable film cassettes I buy from Freestyle. They fit all my cameras, of whatever make, just fine and if you are careful the metal cap on the end never pops off. If you can find a supply of Kodak Snap-Caps, those are the same thing and work fine. As long as you keep the felt clean, the cassettes will work a very long time.
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