I have the same gun and have had the same problem.
I just ordered this hop up
http://www.x-fire.org/sw_m24/chamber...4_chamber.html
Be carefull as there are two Aps-2 models. make sure to get the snow wolf one.It's currently in shipping but I will let you know how it goes.
Tho hop on this gun is NOTORIOUSLY a pain in the ass so I wouldnt be surprised if that's your problem.i have read about people having luck shimming the sides of the hop up arm so if you don't want to pay for the pdi you could try that. You may want to toss a tightbore In There as well, a good thing about the pdi hop up is you can use any aeg cut barrel so it makes replacing it that much easier.