Winchester currently has a load available, is this the one he is using?

http://www.winchester.com/products/catalog/cfrdetail.aspx?symbol=X25202&cart=MjUtMjAgV2lu Y2hlc3Rlcg==

It only manages 407 ft-lbs at the muzzle. I would say if shots are kept very short, it would probably work. Out at 100 yards it is down to 272 ft-lbs. Personally, I would suggest he finds another rifle to use. But that is my opinion. Others use the 22 hornet for deer, and it is pretty anemic as well, but has more energy at 100 yards than the 25-20 at the muzzle.