One tiny little problem with that plan.
The way you get rich selling machine guns is by selling them to normal people. People like us that pay 10 to 20 thousand dollars for one. You do not get rich by selling them to the police, who pay, maybe, 1500 for one.
And if you convert semi auto rifles into machine guns, to sell to the general public, they put you in federal prison for ten years. For each gun. Us - the general public - cannot own a machine gun that has been made since May of 1986.
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.