What is the proper primer to use for reloading Rio trap loads. The win 209 primers I have on hand fit very loose and will not work.

There are only 2 primers that I know will fit. An OEM Rio R209 primer (loading data below), and the Fiocchi Fio 616. I load and use (interchangeably) the Rio R209's, and the Fio 616, even though some say that the Rio R209 is hotter.

Construction of the Rio primers: http://www.rioammo.com/primers.html
Reloading data for the Rio primers: http://www.rioammo.com/resources/PrimerReloadData.pdf

If you are reloading the Rio shotshells, make sure to pick a powder, amount of powder, and a wad selection as to keep the lip of the wads' powder cup off of the top edge of the inordinately tall base wad.

You may have to cut some test slits in a few loads to determine whether or not you have the lip of the power cup sufficiently off of the top lip of the base wad. If it's not, it will look like this (canted/cocked, and hung up):


A proper wad application (20.0 grains of Hodgdon's Clays with a Claybuster CB-6100 wad) will look like this:


BTW, there is no need to totally destroy the shell after cutting inspection test slots in them, - I simply push the lifted plastic sliver back down, load, shoot, then toss the hull. That is of course, if you are using the low-brass blue ones pictured in the first photo.

Thanks for the info, everything I needed to know!