The problem was that my garden was getting littered with plastic BBs from the airsoft gun and steel ball bearings from the slingshot.
The slingshot ammo is very difficult to find once it falls in the grass, but it's the first thing the lawnmower will go over!
So I needed a target that would collect the ammo as well.
This is very easy to make, the only materials I needed were knex and some rubbish from the recycle bin.
Step 1: Building the frame
Be aware that if your slingshot is as powerful as mine it will easily destroy the pieces, so only use if you don't mind breaking a few pieces or you're confident of your accuracy!