Seems like you have 400 spine arrows to bare shaft tune with right now. I would go that route and not worry about spine calculators. A 3 Rivers field point test kit would be a good idea.
I just enjoy the process of working on my shot in the off season. I usually hunt stands where shots are under 20 so I can usually shoot well enough for that range. I do keep a compound dialed in for the times when I'm not feeling so confident.
One arrow practice. I always have a small game/stumping arrow and will often shoot it from stand at a leaf or something right before I climb down. In short, try to prepare as much as possible for a likely shot scenario. I shoot groups during the summer, but switch to one arrow at a time right...
I ran 50gr of powder for my son in my .45 cal Knight. .40 call 200gr Hornady XTP in a sabot. I bought a wood stock to put on it can cut 2" off the butt. He was clay pigeon accurate at 50 yards with a makeshift bipod.
He was 9 at the time.:
I'd say 50gr with a 200-250 bullet would be good...
I have a cheap tripod and a cobbled together holder for my phone that I use to film myself. The thing that I noticed when I was in a real slump was that I was creeping forward before releasing the shot. I was able to see the arrow inching forward from the shelf by just a bit when in slow-mo...