I have…
No idea how to work that, I’m afraid. I’m trying to get a way to use chargers and single load with the same gun but I can’t think of anything, honestly.
I’m in the same position, as I’d like to add a mag cutoff to the SMLE but I don’t know how.
When I can figure out how to have both an internal and external mag, I’ll work on that idea. Sorry to disappoint… 
maybe have a built-in, irremovable internal magazine as a mod? idk not quite sure
also, @FurryDegenerate I get the idea but… SMLEs have detachable magazines, afaik 
I’m working on chargers/clips. I don’t know how to implement them, I’m considering having an internal magazine as an irremovable mod, but I don’t think that would work out well for chargers. It could work for a magazine cutoff though.