What do you plan to do with it when it's completed? As far as ammo, I would just shoot supers out of it for now until you get your suppressor, then play around with the subs. For break-in and plinking I would get some cheap (for 300BLK) FMJs like these:
http://www.midwayusa.com/product/183...ProductFinding
or these
http://www.midwayusa.com/product/528...ProductFinding
For deer/hog hunting rounds the Barnes 110gr VOR-TX is hard to beat:
http://www.midwayusa.com/product/430...ProductFinding