mine has a velocity adjuster... but it's hidden
um... disclaimer: i'm not sure if all aci mavericks were built with a velocity adjuster. not all of the pmi trracers have them.
take your bolt out, look down the front (as though you're looking down the barrel) and if your gun is like mine you should see a hexagon in there. there's like a tunnel that goes from the front of the bolt to the back. and this hex thing goes like around the tunnel if you can see what i'm saying. anyway find an allen key that fits, insert down the front of the bolt and i think turning clockwize will increase your velocity and conter-clockwize will decrease.
more, possibly incorrect, explanation: on the sides of the bolt there are two holes where the thumbscrews go that attatch the pump to the bolt. if you look in those holes you should see brass colored threading. when you turn the velocity adjuster, you're um turning that threading and essentially making the bolt a little longer in back, or a little shorter. when you make it longer, it preloads the mainspring so the hammer will strike harder, increacing the velocity. when you make it shorter you lessen the load on the mainspring, so the hammer will not strike so hard.
a guy at the shop told me that pump players would try to make their guns shoot harder by pointing them down when they cock so it would draw liquid co2 into the gun. so maybe if you tilt the gun up when you cock, it will lower the velocity.
another guy at the shop said that as a last resort, you can remove the mainspring and cut it shorter to lower the velocity. but do this little by little, because you can always cut off more, but i doubt you can un-cut it.
my maverick seems to have extremely inconsistant velocity, so it may be hard to notice the effects of a slight velocity change.
i'm confused about alot of the little nuances of how this paintball gun operates. but i think i have the basic idea.
^^ really long. but i hope it helps
EDIT: ok now i'm thinkin not all the mavericks had velocity adjust.