Since you bought the gun, and paid for all the work, I wouldn't think it would be painful at all, for him.
Is this his only gun? If he is one of "those" (few who post on this sight will fall into the catagory of "one gun only" people) I doubt he would hurt anything with occasional, non magnum steel loads, especially through the IC barrel.
On the barrel flats, you can find information about the guns level of proof. I'm just guessing, but, I'll bet you find the number 900 and a stamp that says 70. This would indicate 2 3/4" chambers, and pretty typical non magnum European level of proof. 76 and 1000 would be a 3" gun, likely a better candidate, for hot steel loads, but, I believe 3" guns came later than this one. Remember, the pressure sneaks up on those fast steel loads, and that is a concern on older guns, double guns, and light guns-your brother's gun falls into all three catagories, so caution is warranted, even if it wasn't much money
Good luck. Somtimes an old double is a money pit, but, sometimes a few bucks spent on an old one makes up for a fine shooter, and there is satisfaction in bringing a piece of machinery back to a good looking and useful condition.
Best,
Ted
