Clever, I ain't. Tenacious, yes.

On your compression tool. All mine are re-worked M die plugs.  Get one smaller, slip fit in the case then turn the base flat.  No lathe you can probably flatten it with a file in a drill press, or mail it to one of us with a lathe . 

Chris’s lee collet die method is similar to old factory loads that used a cantlure rolled into the brass to prevent the bullet slipping with less than a case full of powder, common in .38 special loads.  Important in a Revolver, the bullet has to stay in place on recoil until it’s turn. SS rifle not as critical. You still want it fixed, about thumb pressure fixed. 

More than one way to skim a cat.

Boats

Red Cent wrote on Jan 5^th, 2018 at 5:25pm:


     I don't do much case neck manipulation when making up ammo, either breech seat, or seat in un-sized cases, so don't feel that I have  concentricity problems, but....
     When expanding necks up to a larger size, I use a section of expander the ID of the existing neck as a pilot, then a taper up to another cylindrical section of perhaps 0.035" larger, etc.   With a properly-made plug of several steps, one can take a 30-30 up to 38-55 (or a 30-40 to 40-60) in one stroke, and keep everything straight and centered.
     Properly made, an expander plug with a guiding cylindrical section could be of help, but, since life is short,  FIRST be sure there is a problem, before you set out to fix it!!   

CHRIS
RGChristensen