Ballistic Product says you need a gas seal that seals the entire length of a straight walled hull. They list Federal GM hulls with their BPGS cup and BP12 gas seal. Two piece. They also list their GS2 seal as good for straight walled hulls they also list a 20 ga. felt wad and a OS12 overshot card to take up space for a good crimp. I've got their Buckshot Loading III manual. The same BPGS and BP 12 seal can be used with the Win hull you have. I would recommend a call to BPI Ballistic Products for their advice. I can only say that with the inexpensive factory loaded buckshot that loading buckshot is not cost effective. I didn't have a lot of success loading buckshot.