A guy can't blame wind if he's shooting round groups. Wind doesn't affect drop - if you're stringing horizontally, then sure, it might be wind (or seating depth).
A 10mph full value wind will push my 30-06 pet load about 3/4" at 100yrds. Very easy to change a 0.75MOA group to a 1.0MOA group even in a light 5mph wind if you're not accounting for any drift.
But - again - wind drift is horizontal. If you're shooting 3/4" round groups on good days, and 1.3" round groups on bad days, you can't blame the wind.