NYLES , when you buy and Encore pistol frame the same steps are taken with your "White sheet" as if you were to buy say a Glock. If your buying from say an online shop you will be treated just like if you were buying any other pistol when you get to your FFL to fill out the paper work.
I have an Encore pistol in 308 that I don't use very often and its the frame that I'm building up for my son , I have two barrels for it now one 22lr and one in 250 Ackley improved. both are 18" and both have the muzzel threaded 1/2"-28tpi so if the 250 needs a brake I can screw one on and the 22 is threaded for a suppressor so I can use it for animal control
