Hi JLouis
The bullet I use (pictured) in this post was designed by I believe Dan Theodore. He also designed the one for my Browning 45/90. Both are tapered with the first 2 bands reduced. Base band is 1/10 of an inch and it has a money bullet profile. The design of the bullets is still in the BPCR archives. Originally I tried breech seating and partial breech seating (made my own seater) shot ok but not great. Then I read Wayne McLeran's (Texas Mac)book on these guns and examined the chamber with a lead impact chamber cast. The chamber is not true to the bore (concentric). So no matter how accurate you are with a breech seated bullet the bullet is never truly aligned to the bore.
So the natural progression was to allow the bullet to align itself. Hence my bullets jump at least 25 thou.
Now don't get me wrong - this wasn't a quick process - I went through whole gambit of loading techniques regarding fixed ammunition and after a lot of experimentation I have principles which I use when I reload.
1. Brass is within 5 thou of chamber length and annealed
2. Brass is washed and then sonically cleaned after each firing. I dont care about shiny brass just want the insides clean so that the case volumes are consistent
3. Bullets are between 10 and 10.5 on the Brinell Hardness Scale (somewhere around 15 to 1.)
4. I use 64.5 grains of 2P Wano which is drop tubed with a 40 inch tube. I use powder volume to give me bullet seating depth.
5. I use a 90 gsm tracing paper over flash hole wad. I now use a 15 thou oil Joint material(vegi wad) over powder wad as well as another tracing paper wad.
6. I do not compress at all. If the powder column is outside my parameters then it is re poured.
7. The sizing of case and bullet is described previously. Really all I'm seeking is same clearance between case wall and projectile in each load. By sizing only 3/8 I'm only sizing that part of the case which holds the bullet. There is no neck tension. The cases align perfectly in the chamber as they have been fire formed in that chamber.
I spent 35 years teaching high school Chemistry and Physics - so its in my nature to analyse and experiment.
Cheers macca