Please refer to the write up and the Mcmaster list at the bottom of the page for a materials list.
Step one.
Get your Ultimator

And open it up

Step 2.
Take the barrel and spring

And put them aside
Step 3.
Order a 1’ section of 2.5” ID 2.75” OD Polycarbonate tubing, a pack of K14 springs, and a 2” to 1/2” PVC reducing bushing from Mcmaster

Step 4.
Slap a large metal washer in front of the priming-mech to protect the plastic (Ignore the [k26] spring)

Then go ahead and slide on a cut down K14 spring and bolt the plunger head back on
Step 5. Machining the Plunger tube.
First, cut a slot on the top and bottom of the plunger tube, using the stock one as a guide. I did this using my Band-saw.

The slots were 1.25” wide, on both sides, and went down about 1.75”
Then you will need to line up the plunger tube for the 2 holes on each side that secure the plunger tube to the gun

And drill them out with a 3/8” drill bit

I screwed this part up a bit and had to widen the holes.