How much lead do you displace when you "size something down" a couple thousandths? The gas check isn't that thick and I have the advantage of having been able to look very closely at the "swaged" boolit before the lube and gas check went on. If I had seen signs of distress then I would just have had a nice alternative to my kinetic bullet puller and not a potential gas check tool.
Well, I just miced a .44 cal gas check. The Hornady crimp on type. It is .018 thick. That means you had to squeeze that bullet base down at LEAST .036 thousandths to get that check on. If it can be done consistently without distorting the base, then it should work.
The alloy I make my boolits from would not be easy to swage that much. I think it would crack before moving that much. Because I make them that hard, I don't need a gas check. I do have a GC mold for 44's, mostly because of the weight and nose shape, NOT because I wanted or needed a GC.