I miss my raptor.. thing was a beast..lol..
it could be any number of things from something as already said the velocity it outta whack to a bumper that is missing or out of place , or even the spring itself is really bad/ or not the right one (if someone else has owned it or screwing with it ANYTHING is possible)
open up a light colored towel and start breaking the marker down, as you do it lay the parts out on the towel in the same position they would be in the marker and as you would see them in the exploded view of the manual/diagram
that will give you a much better idea idea of what you could be missing or what needs to be replaced..
clean and inspect all the parts you have while comparing to the diagram..
lightly lube all areas needed and start reassembly ..
if you have issues after that you can always send it to me and Ill fix it for nothing provided you pay shipping both ways and any needed parts..