I totally agree with Mr Loiner. The whole idea of using a filler - something that was not done originally, BTW - is to bring the ball up level with the mouth of the cylinder with the aim of reducing the 'jump' from chamber into the forcing cone. IF your load, say, 25gr of BP OR any of the subs EXCEPT T7 does not fill the chamber, then putting in a known measure of filler such as Crisco, coucous or semolina, then the ball. will do it. This is a modern development - there is no mention that I can find in any documentation of the day that makes mention of ANY kind of filler when loading a BP revolver, and I'm getting my information from a gentleman who owns the largest BP gun store in the Pacific north West of the USA - who also happens to have over sixty years of BP shooting experience, and is a very famous and well-respected figure in a nation of at least ten million BP shooters. I leave it to you to imagine the hassle of loose-loading any BP revolver with powder, filler and ball at a time when you could easily drop in a combustible paper cartridge. By the time you had figured out how to do all that you were probably full of either bullet holes or arrows - maybe both.
As noted by Mr Loiner AND the Hodgdon loading manual, T7 does NOT like to be compressed. So loads have to be figured out to minimize it happening.
So the answer is - use a filler if you've a mind to, the same goes for a wad, either home-made of bought. Having determined the amount of load and filler that achieves just that and sets the ball on the load so that it's level with the mouth of the chamber, or don't - I don't, but others do. Back in the day, revolvers were loading using combustible paper cartridges - I still make them and shoot them. Dropped into the chamber, they are just squozed down into it by the full use of the loading ram until they stop - there is no need to try and squirt the load out of the nipple holes.
But don't leave a gap in a BP revolver.
If you do, please tell us what happened next, or better still, do it on Youtube so we can all see what happens when you touch off that load of 25gr of BP in what is effectively a very short pipe bomb.
Good luck with that.