Sandbags

[Dust]

http://www.theboxotruth.com/docs/bot7_4.htm

Give it a read.  Stopping a 12 ga slug in less than 6 inches.  Seems like a really good back back stop

[Als69GT]

That is why the military puts 2 to 4 layers of sandbags around the bunkers.

Al

[kiwi]

The only prob I can see is keeping the sand in the bag
after a 100 shots theres going to be a pretty big hole...

Apart from that it would be great..& silent

Pete

[Randino]

A big thick roll of masking tap to reseal the main hole perhaps? I've been using a cardboard box stuffed with shop rags for my lighter airguns, and every so often I reseal the box with a few pieces of tape, just to keep it sturdy. Eventually, I will probably need a new box, but that's doable.

Randy

[Dust]

Been thinking about using some kind of sticky stuff to go gelatiny on it, but wonder if the stuff between the sand would cause it not to work as well.

[bodiej]

what about making a heavy "cake" with some sand and an experimental quantity of white glue?  Could put a backing on it to hang as well..

[Jaymo]

Remember, wet sand is NOWHERE near as efficient at stopping projectiles as dry sand. However, for our purposes of stopping pellets, it'll be great. I've thought about mixing sand with sodium polyacrylate(IIRC), the absorbent in diapers. Once it becomes saturated, it turns into a nice gel.
You could mix your sand between 75-25 and 90-10 with bentonite, kaolin, or fireclay. In other words, greensand like you would use for metal casting.
Enough clay to bind the grains of sand together, without turning it into a brick when dry.