I am going to be casting some bullets for my 45-70 in both 405 and 500 grain. The 405 mold has a flat base but the 500 gr mold has a base that takes a gas check. The load will likely use a veggie wad between the bullet and powder and the bullet will be in the 8-9 BHN hardness range. Will I need the gas checks on the bullets if I keep the MV around the 1300-1400 fps range.