After a bit of thought and measuring, we decided it could just (with legs out the roller door) be done in the workshop at home, so cue building a bullet trap!
Very nice! DIY is definitely the way to go, was looking up prices for gongs recently and decided that you could buy several wheelbarrow loads of past-their-best spuds for the price of one of those, and they're much more satisfying to shoot.
Some time ago I was in a supermarket in deepest redneckistan, USA, buying a trolley load of watermelons. The checkout operator looked at the melons and said "Going shooting, huh?". She then gave us advice on the best ammunition types to use for melons, which was generally 5.56 which stops in the melon, the 7.62 just goes straight through without much effect.