[NWPilgrim]

Basically it is a gamble on your friend's part if he chooses not to trim the brass. Most rifles are probably not cut to minimum dimensions so if the neck extends past max case length a little bit it probably will not get wedged in the leade with the bullet causing the excessive pressure HiBC mentioned. But, specs are there for a reason.

You should not count on your rifle having a longer than minimum cut chamber/throat. Either measure it with a chamber casting, or trim to specifications. Forging ahead beyond specifications with no actual data about his rifle is gambling, and every time he reloads those cases and the neck gets longer his odds get slimmer. The sad thing is he may well get away with it once or twice, but eventually the necks will get too long and cause excessive pressure. But the first couple of see-I-told-you-it's-safe experiences will encourage him to keep ignoring reloading directions.

If that is his attitude I would never shoot his reloads in his or your rifle, I would not let him shoot his reloads in your rifle, and I would stand back a bit when he shoots them in his own rifle. Time is not on his side.