I use actual hockey pucks. They aren't heavy (6 oz) but you should be able to find them in sports stores for cheap. Prices have doubled during pandemic, but they are still cheap - $2.. There are 10oz pucks but they are not a common. Can find them in a lot of sports stores or on-line.
Hockey pucks also make good punch blocks. Solid vulcanized rubber. Hard enough to hammer on but soft enough to not dull tools. Also useful for setting up decorative rivets. Easy to drill / carve out the shape you need. Hard enough to set the rivet but soft enough to not damage.
Up here in Canada, hockey pucks are wonder tools. even used them for body work on cars :-)