There is nothing outside of your gun that will affect that, and i doubt its a sight problem, Usually, due to the poor quality of those AEGs, before shooting them you have to check some stuff, (clean the mechbox (too much grease), change the hopup rubber (wich is in most case a POS) and ya sometime you'll have to realign your inner barrel...)
We were there before you so we know what's wrong with those AEGs...
But if you start with a good platform (CA, VFC, Star, G&G...(at least JG)) you wont have that kind of problem... (I didnt mention TM because you usually need alot of upgrades to get them to shoot well and because they are expensive)
Sorry Airsoft is an expensive sport....
"A workout isn't easy, but neither is being fat, make the right choice"