I used to get a lot from simply shooting at a small spot.

5-10mm will do, on a white background.

Depending on the type of shooting, there is often a small amount of movement, so a bit of timing comes into it.

I used to find I could centre better on a spot, or pellet hole, than I could on a ruddy great bull (cant always see the cross hairs clearly).

It also means your zero and grouping ability shows up pretty quickly as well.

It also means that teh fall of shot is easilly seen.

Perhaps just take a shot, then try and single hole the things, it will also show up any change of technique if you are using a springer, and above all it is bone simple.

You will soon see the group sizes come down