Why not just do it the easiest way and drop a line to David at Kynoch and order some foam fillers? They come in bags of 100, cost next to nothing, and work. That's what is used in their ammo if there's more than 3/8" air space. I've found in all calibers my groups shrink and there's little variance in shots, ........and as a result, that's all you'll catch me using! His email is "sales@kynamcoammunition.co.uk"

~Arctic~