Yup you are right, they are all not the same size. I used to have a CA dust cover and it was larger than a G&P cover.
When you mean bolt, Im guessing FAUX bolt (a metal/steel plate the covers the cylinder and hop up of the gun) right? There are 2 ways that I do:
1. The first is to screw the faux bolt to the plastic arm that is connected to the charging handle. When you pull/release the charging handle, the faux bolt will slide backwards/forwards respectively. However, I find that this method has a drawback: You would need to hold the charging handle back in order to adjust the hop up.
2. Inset the faux bolt so that the tip of the plastic arm of the charging handle is between the 2 raised edges of the faux bolt. When you pull/release the charging handle, it will pull the rear edge causing the faux bolt to be pulled back, and when it is released, it will push the forward edge causing the faux bolt to be pushed forward. This method does not require any screwing or fastening, just simply placing the faux bolt between the plastic arm. I personally like this method because when you gently release the charging handle, sometimes the faux bolt will not be pushed forward completely because it does not have enough force to engage the faux bolt which is tight between the mechbox and the upper receiver. This allows me to adjust the hop up without holding the charging handle back. The faux bolt will only be fully pushed forward when the charging handle is released with the greatest force (most stretched position)
This is the plastic arm that I am referring to:
http://www.airsoftparts.ca/store2/im...lde-arm-m4.JPG