First off how many of you have seen a .50 cal MG belt that had pure lead bullets?
They are ALL copper jacketed!
Second, while shotgun shot will settle in shallow marshy area's where ducks feed and ingest it. Large caliber bullets are not near as likely to be ingested by anything. Ducks think the shot is grit, good for grinding up their food. Thats why waterfowl hunting switched to steel shot.
Next, someone back in the 70's was leading a big campaign about mercury & other poisoning in the great lakes. Well someone got smart & pulled a sample from a sturgeon on display in a museum caught more than a 100 years earlier.
Guess what, its levels where higher than current levels!
A lot of the toxic chemicals wash out of the rocks up there, run down into the lake. They are not all mankinds fault at all.
As to feeding sturgeon expended bullets laying on the bottom, well, good luck.
Sturgeon are no dummys, they "taste" before they swallow, unlike ducks.
Leave the Coast Guard alone, they are doing a good job.
Test firing a few .50's in the middle of the great lakes is going to hurt nothing!