Clash in the clouds crank gun

[ZachBoardyHD]

I've followed what the guide says, I got a crank gun from the patriot from stage 1 Wave 11 and when I place it in the weapons room it doesn't refill its ammo but the rest of the guns do? 

Now I'm onto stage 2, the crank gun isn't in the weapons room anymore, does anybody know where I'm going wrong because all the guide says is to place it in the weapons stands with the other weapons which I have done? 

Thanks