Some of the Guys are making 20 VT as well as 17s out of Factory Remington .221 Fireball brass. There's a LOT of it going up for sale now that the Guys have had stashed away.
Or, make it from LC 5.56 or .223. More work intensive but a fun project if you don't mind the extra work.
As far as the .204 in a Striker? WILD recoil from a shorter barrel that may turn you off. Had one and wasn't too pleased because of that.
Lots of options out there. My first choice would be the .221 Fireball. (one of my favorite calibers) Next would be the 20 VT. Will take a 20 caliber barrel to get there.
And remember, it's a "Savage" and you can make it into just about any caliber you can think of. What's not to love about that??