The BR family is annoying (at best) to get feeding in most actions, and the Tempest being built to feed standard diameter cases from an AW doesn't make it any easier. Then you add in the fact that the AWs are welded, so it's harder to make kits for them for the short BR-family cases, and you get a real pain in the ass.
It CAN be done, but I'd personally stick with the Creedmoor case family for a Tempest. Plus there's that whole extra 100FPS speed advantage.
Edit:
HRD also makes a kit with replacement spring and follower.