I would like to load my 45-70 high wall with black powder . My question is what is the proper way to seat the bullet so as not to leave an air space in the cartridge.When loading 70gr.of powder does this automatically mean a compressed powder charge?What about O.A.L.?

Doubt you'll get 70gr. into a modern case and have room to seat any bullet, but you are right: the OAL of a round and the depth the bullet is seated does change the poweder charge allowed.


Rather than start with a powder charge, we'll make that the last step.

Measure the length of the bullet. Seat the bullet to best suit your chamber. With lead in a single shot would be just about as far out as you can seat it and not have it jammed into the rifling AND with enough of it inside the case to permit handling. Measure the OAL...subtract the case length..and you'll have the amount of bullet hanging out of the case. Subtract that from teh bullet's total length and you'll have the length sticking into the case.

OK: exxample (simplified):
2" case
1" bullet lenght
2.6" OAL when seated to best advantage
.6" of bullet outside of the case
.4" seated inside the case

We know for the powder to touch the base of the bullet, its level afer compression needs to be .4" down in the case.

The easy way would be to use a drop tube ( a long hollow tube...30" is prettty common length can be made from a cut ended Al. arrow shaft) and dribble the powder in. this lets gravity do the compression, and as gravity is constant, we get consistant compression from day to day.

Will stillw ant a little bit more compressin...call it .15" of seating. So we want a powdeer charge with this example bullet that will fill the case to .25" from the mouth...with .15" for compression, end up with the OAL we started with.

that might work out to be 61gr. or 65gr. or whatever...depends on brass, sizing of that brass, and the powder used.

Lot of work right?

Other people have just used a a nearly level case and curnched a bullet doen on top, and seem perfectly happy with the results. And i'll admit, i've seen some good shooting done this way...but it's not the easiest method to duplicate time after time.