A common burning barrel, with cinder block blocking the lower air intake "ports".
If a guy's really worried about minor upward dispersal of small odds and ends at LOW velocities, a screen on top.
Get a HOT fire going and a good bed of coals going.
Have your tramp ammo packed in a coupla' layers of WET cardboard.
Stoke the fire and toss the box in on top,...stay away from the drum for the next hour or two,...
The show will be singularly unexciting, indeed BORING.
GTC