Archer sells a wood box that takes Duct Seal ( you can get duct seal at loew's or or the depot it is in the elect dept 6 bars cost about 12 bucks it never gets hard and one thickness will stop a round that goes through a 1 inch pine board ) I built mine out of Oak just like the one in Archer add , I tried the metal ones they sell in K mart and they bend out of shape after a rew rds. My wood trap with duct seal is about 3 years and has had thousands of pellets shot into it I have to replace the duct seal every once in a while but it still keeps working. ) I have shot B30 , B21 , RWS 48's as well as many other magnum rifles with out them going through the target, in a 10 M setting. Howie1a