In Utah years ago the DOC Rented Model '94 Winchesters in .30-30 from Gallenson's, a local pawn shop and sporting goods retailer in Salt Lake City. They reserved a group of guns for the DOC that they would not sell. They were used for several executions over the years. I don't know if they still have an agreement with DOC.
In reality, do either gun or caliber matter so long as they are adequate? The Model '94s were used because of their simplicity of use since the shooters selected for an execution were not necessarily particularly familiar with firearms, and the caliber was adequate. As I recall the firing squad consisted of 10 shooters. I do not know how the shooters were selected, but I do know they were not volunteers or prison employees.
And old tale ......Some were loaded with blanks.....So no really knew if thay had a blank or a bullet.....So the tale goes......All the rifles were pre-loaded so no shooter knew what their rifle contained......Is this fact or fiction???