I'd guess Midway's handleing this the same way I and other vendors did in the past (regardless of product). Once they have more than a certain number of backorders they quit taking them until they can catch up. That way customers dont start getting bent out of shape thinking. "CRAP! I backordered that three months ago and havent heard a thing! JERKS!" If that happens Midway not only looses that one order, but any future business from that customer because he feels Midway gave them the shaft.
My money would say the boys at Midway have lost MUCH sleep trying to figure out how to get you / me the ammo we want to buy! Their just caught in the middle along with all the others.
My wife deals in metal sales every day. She and others will tell you while demand is up, & brass, copper, steel, and lead are a little harder and more expensive to get in large quantity these days, the supply of raw materials would NOT cause anything like the bottle neck we're seeing in this industry! Dont believe anyone trying to use raw material availability as an excuse.