Grouse loads may be as close as a .375" Round Ball mould.
: Swaged to whatever size the throat is, ie: .367", .368", .370" - whatever - they can be set at the case mouth and held there by pressure into the case mouth. A few grains of 5744, worked up until reliable velocities and accuracy are abtained at 25 yards. I suggest starting at 10gr. - NO FILLER. This goes for either 57mm or 62mm case - or .358" Round Ball for any .358 calibre as well, .35 Rem though .358 Norma Mag.
: Round balls are fun, can be very accurate, kill bush 'chickens' well and can shoot very close to the sights in most rifles. When working up loads, if one sticks in the barrel from too-light a load, they are very easy to push out the bore with a normal rod, unlike longer bullets, but then, it doens't take much breech pressure for the gun to spit them out the muzzle. Target velocity is around 900 to 1,200fps. WW alloy works perfectly.