So you are saying that in fact its a Russian Krupp M-1909 122mm field howitzer? I still think the bore looks too big, and the cradle seems too large to be the 122mm weapon, which had a narrower and shallower cradle; if someone goes there they should try to measure the bore and look at the breech markings (ie. ignore the signs, I sometimes find mistakes at these museums) as that is the only sure fire way to put doubts to rest. This suggested method may be somewhat risky in Iran, however.