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!
Step 2: The Target and Collector
Make sure that the box you're using is weak enough to be penetrated by the airsoft gun/slingshot.
When filling up the middle make sure to use the weakest stuff at the front, if you pack something hard up against the box nothing will be able to penetrate.
Basically you want the BBs to penetrate the first few layers so they get stuck, but not to penetrate through the entire box.
Ideally, the top picture is what you want.
Step 3: Target
This is more important if you're using a slingshot, it doesn't really happen with an airsoft gun.
Draw circles on it so you can pretend it's a professional target!
Step 4: Shoot!
In my case, if I aimed too high I would probably smash my neighbour's window,
but as you can probably tell from the photo, that's a shamefully close distance to miss...