x39 for deer?
Depends entirely upon the deer, the rifle, the hunting situation......
The tiny deer I saw in Maryland an Virginia? .22lr oughta do the trick: they could not have weighed 70 lbs soakin' wet...... Really big deer? They migh not decide to give you the perfect broadside shot..... can you pass up poor angled shots?
Using a short barreled AK will cut some velocity, of which the x39 does not have in abundance in the first place...... it needs all it can get...
.... also, will the rifle used be accurate enough for the situation? A 5 inch group off a rest at 100 yards won't cut it under field conditions in many cases .......
....the hunting situation.... are you ambushing deer from a stand at really short range? With good ammo, not a problem. Hunting a hayfield where a 300 yard shot is possible? That's a problem.