But the original AR-10 is definately not the same gun as today's AR-10. And if the AR-10 has a picatinny rail and a barrel stepping (like on 16" carbine A4 models) then I suppose you could fit an M203. But AR-10s aren't issued to military and you can't own a M203 without a destructive device liscense (and in my case, I can't even buy the fake Cobray flare launchers, because flare guns are banned in NY :P) so it seems like a slim chance this is a neccesary modification.
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