In the quest for accuracy with cast bullets it appears that breech seating is of tremendous advantage.

It also seems that breech seating is done with single-shot rifles.

Has anyone done it or seen a breech-seater for, say, a Remington 700 or 40x?

I have read of this being done. Got a friend with a lathe? The machinist turned a solid brass case on the lathe .050" short on the neck length, and then drilled it thru with a 1/4" bit. Then he turned a section of drill rod to that same neck diameter for the .050" mentioned. The rest of the rod was turned to .245 and cut the length of the solid case minus .050". The inside of the dummy case was also tapped, and a headless hexhead screw screwed in flush. The idea was to create a dummy solid case that with a hex head inserted into the rear could have the "plunger" on the front moved back and forth to allow for adjusting breech-seating depth into the chamber throat. You still have to gently place the bullet into the throat area and ease the solid brass dummy case in behind it with the bolt as you close it. The advantage in single shot rifles and Schuetzen shooting is to create a slight "interference fit" and so seal the bullet in the barrel. A lot of these rifles have no leade or throating.
Hope this helps.

Rich
DRSS

Thanks, Rich!

Lots of little pieces of this puzzle I'm chasing. I'll post more when I get to the building/testing stage. Still in the thinking and planning phase.