Since you took your barrel off your 15-22 it is of course chambered. I hope this isn't too simple of an answer, but the chamber is cut in the breech end of the barrel for whatever cartridge the firearm uses...in your case the 22 long rifle. I am a bit puzzled why a gunsmith could not tell that a barrel has been chambered, unless I misunderstand your question, and why he would care since I assume that you were having the muzzle end threaded? If this explanation isn't clear please post again, and we'll help you out.
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