Yes it is POSSIBLE to make a passable .25 Stevens from .17 WMR, but it's a PITA and my experiment, for which I had much enthusiasm, has been on back burner all winter.  The Winchester (brand) .17 WMR brass is so brittle that expanding it gives me  a dreadfully poor yield.  I shelved it before I did more than a few fire-for-function.  

By shortening up and making .25 Short it should do much better, but the Short in a Long chamber isn't going to be very accurate.    

I bought one box of Hornady, and another of American Eagle, in hopes that one might be easier to form, but haven't even opened them.  

Another disappointment is that the .17 brass is thicker and harder than the original stuff.  My Stevens "boys' rifles" will not fire it.  Hammer blow too weak.  A Model 44 will fire it, though.  If that outside hammer is as heavy as it looks, it should do it too.  But it's all just speculation until he has the rifle in hand.

Over the winter I played around with adapters for the .32 Long rimfire.  One thing I quickly learned is that using Ramset charges in the 1 an 2 power ratings is OK, but 3 is more than the adapters can stand.  Using 4 and 5 power level in a .25 Stevens rifle may be too much, IMHO.  

All for now.

Phil

Body diameter of a new .25 Stevens cartridge is .277, rim .337, so they'll be a bit loose, but they'll fit.

The body diameter of these .17 rimfires I've been playing with measures .268, which is probably no coincidence.

well, what did it turn out to be?
inquiring minds want to know.

Aaron