A similar problem I had to SVD (atoz).
For about 70m the BBs flying straight, then rise and continued to stand up for more than 110-120m until fall.
What I did that he did and vindicareassassin in the topic "THE Holy Grail of building your DMR AEG" and specifically to cleaning of the rubber HOPUP from the lump.
http://www.airsoftsniperforum.com/phpBB/phpBB3/viewtopic.php?t=889
The raising of BBs stopped, and now shot is a straight line as far as has energy.
I hope to help
Dulas
For about 70m the BBs flying straight, then rise and continued to stand up for more than 110-120m until fall.
What I did that he did and vindicareassassin in the topic "THE Holy Grail of building your DMR AEG" and specifically to cleaning of the rubber HOPUP from the lump.
http://www.airsoftsniperforum.com/phpBB/phpBB3/viewtopic.php?t=889
The raising of BBs stopped, and now shot is a straight line as far as has energy.
I hope to help
Dulas