[reezo]

As usual (kudos!) I agree with everything that was wrote here. If I might add something:

1) What you are experiencing is very common..but it is not so common to read it blatantly reported on a forum. Some users don't care, others don't notice, others just use full auto and have no idea what trajectory means XD

2) One cause of the problem could be an incorrect hop up rubber placement. Here are two diagrams that might help you understand.

3) You might be experiencing a canting error, or error of cant.
Long explanation: http://www.riflescopelevel.com/cant_errors.html
Short explanation: http://www.arld1.com/impactpointvscantangle.html

4) Your barrel might be bent or pushed by spacers (I'd say this might be more rare..)

 

[reezo]

Wow thanks for the links!! It's the first time I see them!
Especially the second kicks @ss very easy to understand canting!

Wolf

Thanks Wolf! I am going to put this in my database, it's definitely useful. I might rephrase that and make the entire process of tuning etc. more readable..great guides, true!