brudford
For breech seating, I have always had the best accuracy with smokeless using no wad. You can put a cork in the case mouth to prevent powder from spilling out of the case but remove it before chambering the cartridge. Your 20:1 is the ideal alloy for smokeless (at least for starters). Your bullets should be groove diameter or even better if they are .001" over groove diameter.
I did a post a while back on how to determine the proper bullet seating depth. If you can't locate it with a search, PM me with your email and I'll be happy to send it to you.
As an aside, if you decide you need a wad, do not seat it down on the powder but keep it .10-.20" off the powder.
Good luck and I think you will be pleased with your breech seating accuracy.

35 Caliber wads punched from sheet cork are easy to get past the case mouth and will stay in place inside the case. Push the wads into place with a short rod, just under case mouth diameter. Put a mark on side of the rod to line up with the case mouth at proper seating depth. The 35 caliber cork wad will stay in place against the tapered 32-40 case walls anywhere between the case mouth to just ahead of the powder charge.
While seating a cork wad off the powder is a straight forward task, the worm in the apple, at least in my experience, can best be summed up as erratic accuracy and not worth the effort.

Some powders benefit from the powder being confined. 4100, Enforcer and the old H108 all perform well with a wad placed about .050” off the powder with the case tipped down so the powder slopes at the base of the case. 4227 and 4759 work a little harder with wad down on the powder and in moderate loads with modern barrel steel will do no long-term damage. Some experimentation and consistent loading technique and working with your chronograph is required to see real results.

40 Rod