So doing some measurements and the RMC cases I have will hold 35 grains of 2f black or 34 grains of 1f.  I've always been of the belief that black powder should fill the case with no air space.  

These measurements would be about 15% over the old factory load.  Would it be better to back off to 30 grains and use a filler or go with the full case is better.  I've breach seated with smokeless before, but this is my first with black powder.  whats the school of thought for breach seating. 

Thanks

If you can’t have an air space with Blackpowder, how do you breech seat or muzzle load at all?

If the bullet is not seated in the case, there is an airspace.

To breech seat without an air space:
- Fill case full of black powder to just barely below case mouth

- Press an over powder top wad (cardboard or veg) in the case mouth so it's even with case mouth. Adjust powder charge so that over powder wad is pressed on the powder and even with case mouth.

- Adjust breech seater to place bullet base so it touches the case mouth when a cartridge is chambered - or - add a felt wad between case mouth and bullet base and set bullet depth so there is a snug fit between case mouth and bullet base.
Result - no air space.

As an aside: The whole no air space is not as big an issue as sometimes stated (IMO). Back in the day (c.1890-1920) shooters who breech-muzzle loaded rammed the bullet down the barrel so it sat about 1/16" ahead of the case mouth. Literally millions of rounds were so fired without ringing the chambers. I'd call that an air space.

So let me rephrase a little.  With my 32-40 and other rifles that I breach seat with smokeless I use a small circle of ashless filter paper to hold the powder (usually 4227) in proximity to the primer and to keep it from spilling out.  Obviously the case is no where near filled to capacity.  However, with black powder I run into a different problem.  The 28-30 cases I have hold about 34-35 grains by weight of black powder which is above the nominal 30 grains factory load.  Should I cut back the load to 30 grains and use a filler or go with  the 35 grain load essentially filling the case .Should I top with a .003 fiber wad, a grease cookie, both or none.  

FWIW i generally seat about 1/16th inch ahead of the case mouth.  My normal filler if loading fixed bp ammunition is cream of wheat.  

Thanks

If you are going to shoot black powder in your .28-30, .32-40, etc. - fill the case with powder, use a wad in the case mouth to hold in the powder. Wads you add only add variables that don't improve accuracy (IMO). Your .28-30 cases don't care if they have 30 or 34 grains of black powder.
Forget about over powder wads for your .32-40 smokeless loads, again, wads only add a variable that doesn't improve accuracy. Sometimes a wad or two are necessary but you got'ta experiment some to find what produces best accuracy for each rifle.
The felt wad I mentioned in my previous post works for one of my rifles but not another.

The 28-30 appeared circa 1900 when BP was on its way out.  A preferred accuracy powder was King's Semi-Smokeless.  4227 gives very good results with a lot less hassle than lots of BP in a small bore.  I've been shooting 11.2 gr. 4227 with a breech-seated 140 grain Hoch cast about 1:20 tin & lead, Emmerts lube, for years,  Stevens 44 action.  Works fine.

Thanks everyone for the great information!