If you had been hitting these geese and not bringing ?em down then the finger of blame would point to your cartridges not being up to the job.
Instead, missing them cleanly suggests you are not dialling in enough forward allowance.
Remember that greylags ? and every other goose come to that ? fly a lot faster than you imagine.
A wildfowl guide once told me a goose travels about 10 or 12ft with every beat of its wings so you need to get those gun muzzles further in front than you would when, say, shooting a pheasant over the same distance.
There isn?t a knack as such to shooting geese but it definitely helps to concentrate hard on the head of the bird, and ignore its wide body ? the only sure way to get clean kills is to hit them in the head or neck.
And the final thing to remember is distance.
A goose is a big bird and often appears to be within range when it isn?t.
If in any doubt, don?t shoot.