Can't give you a great answer, but I can say RL-22 (a great powder for the caliber) is regarded as pretty sensitive. There needs to be a lot more research done on the subject, but the powder manufacturers aren't going to do it.
Also, many variants of the "same" powder (such as 4831 types) are often different in how they deal with temps. You're right to tell him to be careful. I'd say just load him a ton of rounds so he can sight in there. He should be grateful to reimburse you for a couple of boxes of ammo if he's paying hundreds for the airfare.