If they're smaller than his girth, you should either increase the rat size slightly, or stick closer to a 5-7 day schedule. Also, why are you moving him to another tub to feed? Wouldn't leaving him in his enclosure solve the problem of him striking at you on feeding day? There are dozens of threads on this forum where the general consensus is to debunk the myth of feed-related cage aggression and point out the minimal risk of substrate ingestion causing impaction.