in a 410 chamber. So 410 is about 50 to the lb. 12 ga is said to be 12 rd balls to the lb,but that's not accurate, either. A rd lead ball, .72" in OD, would not weigh 583 grs. 7000 gr in a lb, divided by 12 is 583grs. The elongated 12 GA slug is 1oz, 438 grs. So a rd lead ball, 12 ga, would weigh less than that.
weigh 104 grs, say 105 grs,since you claim it's between 67 and 68 ga. A .33" 00 buck is 60 grs, IIRC. a 410 slug is rated as being 1/5 oz, which is 85 grs, and it's elongated, so a round ball of the same OD would weigh less.
Just to clarify a bit - the hollow slug is the normal Foster-style found in commercial ammunition meant for smoothbore shotguns. I have experimented with several solid configurations (as have others), but:
1. In a 12 gauge, they are considerably heavier than 1 ounce.
2. I have been unable to find a design that even approaches a true, nose-on, flight. (From a smoothbore).
I have built a 1 1/4 ounce slug that works quite well, but it is in the more traditional, hollow style. A 1 1/2 ounce slug is in the works.