Whoa, dogie..... Charley nailed it..........
When I read the OP's first post and saw the reference to using pistol powders for fire forming, my mind immediately took a left turn and all I saw was someone forming 17 HH brass from 22 Hornet brass which is what I was referring to with my reference of using 9.0 grains of Unique when I formed hard to find 17 HH brass from 22 Hornet brass several years ago. My bad.
If you already have 17 HH brass, trim the length if needed, load the brass up with a good stiff load of an appropriate rifle powder topped with your chosen bullet and pushed by a scarce primer to make it all happen, and go kill something.
You can buy a box of factory ammo and shoot it in your rifle and the shoulder might move 0.002" simply based on your rifle chamber. And neither you or what you kilt will know the difference. Don't overthink things. You completely drove this old man with apparently poor reading comprehension into the ditch doing so.
Sheesh......
-BCB