I haven't been to the Knob Creek Range, but I had a lot of opportunities to go through rounds with Uncle Sam's canoe clube (U.S. Navy). 

 

I would offer this rule of thumb for shooters considering a Class III (transferrable) weapon.

 

1.  If your Class III weapon is magazine fed, buy your ammo by the case.

2.  If your Class III weapon is belt fed, buy your ammo by the pallet.

3.  If your Class III weapon is a Mini-gun, buy your ammo by the pallets loaded in the back of a 5-ton truck.  (Minis have a maximum cyclic rate of 6,000 rounds/minute or 100 rounds/second.)