Honestly, I would say scrap the MR5.
I own and have used with FSR:
Milsig Paradigm Pro
And used on an outdoor gun range a buddy's DAM against all of these. The 468 after I put a reg on it, is pretty accurate, but the best, shot-shot velocity consistency, and total accuracy, is my BT Tracer by FAR. I made up a little side mounting sten like mag for it. It takes cocker threads, is closed bolt, and would be easy enough to put a reg onto for further velocity improvement.
I lowered my MR5's spring strength, adjusted the pressure with a plamer reg, have a barrel/breach adapter for it so I can use other spyder threaded barrels, but it still kicks quite a bit when shooting and has lots of moving parts and the rounds don't sit in a breach. It's just not that great of a platform to be using for such a precise set of tests, in my opinion.
If you want, I can mail you out my Trracer. The mag system can be a bit tricky at first but its nothing an engineer can't figure out. You can also have it right side up too and remove the variable of the round not being fired/seated properly each time due to the open bolt aspect of the MR5. I'm not using it much anymore so if you want, and think it will help as I do, I can send it your way.
Also you'll need to get the centrifuge thing going too. I don't think the tapping is cutting it. I've got a game in a few weeks in Houston I'll be going to, but after that I can send the centrifuge out too if you want. You'll just need a cordless drill to spin it.