I call em DINGERS,,,They are fun. With my old bbl I found most commercial gongs would be dented quite badly. 1/4" thick and all.
3/8" seem to hold up pretty good,, till my brother shot a hole in it with his 270.
I don't think any of em last forever, but they are fun.
Right now I got this heavy walled 8" pipe, it doesn't ring but puts off a nice "CLANK" any where from 50 to 100 yrd.
I used to shoot with these guys who also had snout loaders, and we would have these competitions. We'd set one of these up and then somebody would say, "Ready?,,,,,SHOOT" and the first to shoulder and hit the dinger won.
They are fun with Hog Leg too, 50,,54 and all, set em out 40 yrd or so.
Don't tell anybody, but I got me this Kentucky Peestola,,its a hoot.