I have been experimenting with the 2 1/2" .410 cartridge lately and now am looking into loading buckshot charges. My question is focused on the diameter and weight of round balls to load. The nominal choke constriction for the .410 is .390" at the muzzle wfor the tightest choke constrictions posted by owners who have measured their muzzles. The load recipe is:
444 Marlin cases
large pistol primer, standard
13.0 grains #2400 powder
Nitro card over the powder
no shot cup
round balls (diameter .360"), #OOO Buck, OR
round balls (diameter .375"), for 36 caliber black powder revolver.
Over-shot card held in place with Elmer's glue.
The diameters of both of these size balls should not create in issue at the muzzle and each cartridge will hold only three (3) balls at a loading. However, the WEIGHT of the shot troubles me. The standard shot weight for these shells is one-half ounce (218 grains). Three balls of .360" diameter weigh 213 grains whereas three balls of the larger .375" diameter weigh 240 grains, well beyond the standard weight for this cartridge and powder charge. I am leaning toward reducing the powder charge for the heavier weight boolits down to 12.0 grains #2400 powder to avoid a pressure issue. Perhaps there are other ways to approach this issue. If anyone here can speak to this question from their experiences, please chip in. All responses are welcomed and appreciated. Thank you.