Does the manufacturer of the conversion kit recommend a particular brand of .22 ammo?
I've never owned such a kit, but I do have a friend that has one. I can't recall the brand or model, but I do recall him saying that it was ammo specific.
If the manufacturer doesn't recommend any one brand of ammo, buy several boxes of differing brands and weights. Spend some hours on the range experimenting.
Or....just call the manufacturer and run it past them.