It can be a combination of items, heavy gun, cheep carts, shoulder fit , eye sight ..Use half descent quality carts , cheep stuff patterns badly (what I have tried) & will not help you confidence, A heavy older gun will make you ache & the muscles tension wrong, A non comfortable shoulder fit will alter all your shots & try one eye closed , both open on a target 30/35 yds back .
When movement is a target shoot a good yard in front the direction of travel. stand well balanced.
If you can eliminate all the niggles , relax & enjoy, don't shoot too far out ! I seen lads trying