I know there aren't very many of these left, but I decided to make a writeup anyway.
Diagram of parts
Start with your stock SM500.
Remove the round orange pieces which reside where I have circled.
I used my dremel and just cut them off, but it can also be done with a pocketknife and patience.
Next unscrew the yellow pieces on the handle.
Then remove all of the screws. Don't forget the ones the yellow piece were covering.
Take off the shell and take a good look at the trigger assembly.
Now, take the pump and tank assembly out. Be carefull not to lose any springs.
Cut the barrel off where the orange muzzle piece ends and set aside the pump and tank.
Now remove the white plastic from the muzzle by any means necessary.
I made parallel cuts with my dremel and pried off the bits.
Take out the spring and peg thing. Then drill out the inside of the muzzle.
To this. (mine isn't quite done)
Make sure your barrel materiel fits snugly.
Get that tank piece back out and cut the white barrel so it is flush with the purple shell.
Put the muzzle piece on the barrel, then put in your barrel materiel as far as possible. Pull out the muzzle.
Now you know the distance between the back of the muzzle and the front of the tank.
Then wrap e-tape around the exposed barrel piece until it is flush with the back of the muzzle.
After cutting off any excess tape, jam the muzzle into the white barrel piece. It should be tight.
Wrap a bit of tape around the outside of the white tube so it will be snug with the shell.
Put everything back together.
There you go.
I get similar ranges to an AT2K
WARNING: Do not plug the pump. It is very easy to damage the valve beyond repair.
Thanks to Nerfer34 for parting with this rarity.
Edited by bobafan, 20 January 2008 - 11:20 PM.