The final product will look something like this:

Heres what you need:
1. regular bic pen
2. paperclip
3. hacksaw
4. round file or dremel
5. epoxy (dosnt have to be super strong)
6. 1/2'' Cpvc
7. E tape
8. crossfire nerf blaster
9. hot glue
first, open it up and take out the barrel (mine is already cpvc'd). wrap the end of some 1/2'' cpvc in electrical tape until it fits loosley in the inverted plunger. then cut out a ring of E tape, leaving some at the end. then take out the tape you cut and replace it with the O ring that was on the original barrel. when you are done, it should look like this:

next, cut the orange tip off of the barrel. dremel or file it out so that the /1/2'' cpvc fits snugly.

then, epoxy (i was lazy and used hot glue. NOT a good idea) the barrel into the orange ring. make sure you mark it so that it fits well with the plunger.

now that your barrel is done, lets move on to the plunger.
my first idea was to use some small copper pipe that i had lying around for the priming rod. I then realized that doing that would make the plunger weight much more than needed, not to mention, a pain in the ass to put on. the priming rod that i ended up making was out of a bic pen.
first, take the insides out of your ordinary bic pen

then, put it on the back of the inverted plunger, and mark where the sides of the pen are on the X. then, get your hacksaw and cut next to those marks so that the bic pen fits inside the grooves (my first idea was to drill a hole in the middle of the X that would fit the pen perfectly. Yes, i am a dumbass.)

next, epoxy the pen in the grooves.

also, if your catch on the plunger already started to crack, put some epoxy over that too

since my epoxy was weakass, the priming handle fell off after a few shots. to fix that, i drilled a tiny hole near the base of the priming handle and stuck a part of a paperclip through and hotglued it there. this will also increase spring compression a little bit.

your plunger is complete! now we have to make the hole in the back of the shell, which is actually a real bitch because of that little groove in the back. just file out where the bic pen will stick through, and make sure it does not rub against the sides.

heres another

Now just lube it up, put everything back together and you got yourself a Nitefire!
the internals:

once again, the completed blaster

Ranges are around 40 ft with a rubberband on the back
Note: DO NOT cut your barrel like i did. the gun looks really cool when you dont see the barrel sticking out, but it shoots downward. i later fixed this
oh, and also, i apologize for the blurry pics. my camera wasnt working very well.
Well, what do you think?