What you will need is:
thick walled PETG
PVC
1/2 inch FBR
dremel
plumbers goop/epoxy
hot glue
hot glue gun
ruler
screwdriver
Now lets get started.
First you are going to want to open your gun up and throw away the barrel and air restricter parts. You are also going to want to through away this part.

Now you need a barrel. So cut off a 4 1/2" segment of PETG and goop or epoxy it onto the plunger tube. It should go right over the nub on the end of the plunger. To make sure that the barrel is strait befor you glue use a little bit of hot glue to hold the barrel on strait when the goop or epoxy is drying.
While your barrel is drying it is time to work on the shell of the gun. You are going to need to dremel out the notches in the shell in the places shown below.

The next step is to put ammo holders on the gun. You are going to want to cut a 2 1/2" and a 2 1/4" pice of PETG. Now hot glue the larger of the two pieces into the top ammo holder spot. Then glue the smaller piece into the lower ammo holder. Now cut two 1 1/4" piece of FBR and shove them into the ammo holders. This way the darts don't go to deep into the gun on accident. It should look like this.

Now that your barrel is done drying you are going to want to cut a 4 1/2" section of PVC. Now dremel the inside of the PVC a little so the PVC can slide over your newly added plumbers goop. Once the PVC fits, hot glue it to the plunger so it will stay in place.
The next step is to dremel the back ring on the plunger tube. Dremel it to look like this.

Now you are ready to glue your plunger tube into place. This will help increase ranges because now the plunger head can do it's full range of motion in the plunger tube. You are going to want to hot glue it into this spot.

Next you are going to want to increase the seal on the plunger head. To do this put a few layers of e-tape under the o-ring. Make sure you wash the plunger head before doing this or the e-tape won't stick.
Now you are going to want to replace the spring. I used a RF20 spring with a stretched out NF spring over it. If you do the same spring configuration you are gong to want to stretch the NF spring to be this long so it wont rattle in the gun so much.

Top: RF20 spring
Bottom: NF spring
It won't rattle now because when they are on the plunger rod the RF20 spring is stopped by the plunger heads teeth and the NF spring overlaps the teeth.

Now your done just lube up the plunger tube and put everything together.
The ranges I got with this gun are about 75ft.
Thank you.