Guys, Being new to this I thought I would take a stab at building my own breech seaters since I'm too cheap to buy one. These will be for my Pedersoli 45-70 RB. After a lot of reading I came up with two versions. The first is not a new idea, just a different twist on the plugged case "model". I cut three pieces of 7/16" dowel and marked accordingly. The first one labeled "seater"; is cut approx 1/4" short of the case mouth and will use to initially seat the bullet into the throat (I didn't like the idea of dropping the bullet in, most probably not straight either; this gives me a better case at a better alignment). The other two pieces of dowel are cut +1/8" and 1/4" beyond the case mouth. After I initially seat the bullet, I'll remove the case and seater dowel and replace with either one of the other two to seat the bullet home. Now in the 45-70 case, I can use #10 washers under the the dowel and the case to get varying seating depths. pic 1 shows these.
Version 2 breech seater is shown in pics 2 & 3. The "Ram-er" is a aluminum binding post from ACE hardware  that is 1-1/2' long and internally threaded at 8-32. I cut a 7/16" dowel 1-1/2" long and epoxied that into the case, let it set for 24hrs. I then drilled a 13/64" hole from the primer hole for the entire length of the dowel epoxied in the case with my drill press. This acts as a guide sleeve for the aluminum binding post. I then took a 8-32x12" threaded rod, inserted thru the case and dowel sleeve and screwed on the binding post. Added some 8-32 nuts with a lock washer to act as a stop that can be adjusted to any seating depth. Added on a handle with a shorter aluminum binding post and it's complete. I've seated a couple throw aways and seems to work fine. The only remaining work item is to put some bends in the rod to clear the Rolling Block trigger since there's not a straight shot into the bore. Very cheap and functional.

Creative and budget-savvy; but----the small diameter shaft might also flex, especially with a dogleg bend, and could result in a slightly tilted bullet entering the rifling.   Most of the "push-seaters" use a heavier more rigid rod.