Originally Posted by kalnaren
Hop-up changes. You will probably need to do minor adjustments depending on atmospheric conditions, and when one cleans the barrel it's usually a really good idea to dial it off. M16-style hop-ups are also known to not hold their position.
Hop-up isn't static. Get used to playing with it.
Mostly due to inner barrel wobble, and having no solid connections in it's design.
There is a reason any MP5 will outshoot any Armalite for accuracy, MP5 hop up unit and inner barrel is held solid in three places............. all Armalites are held in place by a loose tongue and groove joint between the hop up unit and the breech of the outer barrel, and a small spring. I've never seen one shoot less than 2inches at 30ft distance, so don't get your hopes up about it being a tack driver.