You don't have to worry about catching big beaver in Comstock Cages.  Pictured above is a 61 pound beaver taken in a 12x12x36, the largest beaver taken in the smaller Comstock Beaver Cage Trap to date.  Information and pictures acquired from others using traps with the same size opening, 12x12, indicate that this is not an unusual occurrence, but to be expected.  I have also seen a picture with a 58 and 64 pound beaver in cages of this size.  Though the traps are only 36 inches long, it took a 44 inch long beaver!  

This is another 66 pound beaver taken in a standard 12x18 Comstock Beaver Cage Trap.  One trapper in Massachusetts claims to have caught dozens of 60 pound beaver, some 70 pound beaver and even a couple of 80 pound beaver in untrapped areas in the Comstock Swim Through Beaver Cage Traps.