Hi Rich,
I did some comparing on-line and Solvarr's ammo can is a SAW can, the regular .50 cal cans are a bit smaller. I don't know how this would effect the forge performance. The only thing I can think of is the smaller can has a smaller cubic volume (remember the 350 cubic inches for one burner?) - could this possibly be too much heat for the refractory to handle??? More experienced people than me would know. If people are interested, I have found quite a few SAW .50 cal cans on ebay - some entries are even for multiple cans 2, 3, 4 ... 96 (someone is selling a skid of 96 ammo boxes for over $300.00).
Hope this helps.
aeneas