crosswind, head and tail winds phil, hence why I keep going back to 10.6 in bis mags, there really is a lot of difference in flight
Read this it might change your mind on light pellets http://www.airgunforum.co.uk/forums/showthread.php/174275-Massive-177-JSB-Pellet-Velocity-Test-0-50-metres
I use to think the same but after trying FAP in .22 and AA express in .177 they knock spots off on other pellets