Hop up unit
 

My ak gbb feeds multiple bb's and at random 2-3 come out of the barrel in one trigger pull on the same cycle, and full auto is even worse. They also get forced down into the receiver and cause jams with internal parts, any Idea why this happens.
Thanks Guys

Coast Recon you may want to post that in the doctors corner section.

I am interested in getting one of these with an NPAS kit. From what I have read in my initial research they have decent externals which will hold up. As far as the internals go what will I have to replace so far I have:

Bolt
Bolt carrier
Hammer
Hop-up

I was also wondering if placing a rubber pad to soften the return blow would affect the firing at all considering it forces the bolt to rest a distance from its normal position.