From some quick googling...

A 53' trailer has an internal volume of 3489 cu-ft.
A 50-cal ammo can with exterior dimensions of 11x7x5.5" has a volume of 423.5 cu-in, or 0.254 cu-ft.

So, you could cram 14,236 50cal cans in a 53' trailer.

The average "full" 50 cal can weight about 35lbs (I recently weighed a bunch for reasons...) => A "full" trailer load of "full" 50cal cans is 498,260 pounds!