Get into Ryman stationery in your High Street. Buy a pack of their 30mm self-adhesive orange discs to use as targets.
Put one disc on each of several sheets of A4 printer paper.
Using a measuring tape, place one target 10 yards from your firing point, one 15 yards, one 20 yards and so on.
Now -
using exactly the equipment and shooting position that you will be using in the field - fire a 3-shot group at each target in succession, nearest to farthest.
The range at which your first bullet strikes
outside a 30mm disc is beyond your maximum field shooting distance. Restrict yourself to closer shots.
maximus otter