Building dummies without loading dies.
Something I learned through trial and error.
Super Glue is too brittle.
Clean brass. Sizing brass is not necessary for rounds not intended to be chambered in a firearm.
For Boxer primed cases. Use a socket as a base. Use a thin steel punch and punch out the fired primer. Lee makes a nice tools for .22 and 30 caliber cases. Berdan primers must be drilled out, unless you have a way to force the primer out hydraulically.
With the help of a matchstick or toothpick, smear RTV-any color- inside the case neck.
Insert an appropriate projectile into the case neck to the proper depth, rotating to obtain even sealant distribution.
Wipe off excess sealant with a paper towel.
Lay the cartridge down on your work bench, horizontally. Standing case vertically runs the risk that the bullet will slide into the case cavity.
Allow RTV to cure for 24 hours.
Finished demo cartridge.
Note: Using fired, unsized cases, these may not chamber in your gun.
Note2: In the interest of domestic tranquility, Don't get RTV on the kitchen table.