Southern Brisbane Nerf Club

Friday, 7 February 2014

Direct Plunger Centurion

Urgh. Centurion... I will curse that word till the day I die. But, at the very least, I've made it suck less.

More after boing.

I wouldn't consider myself an "experienced modder". I dabble. Compared to the other things that modders have done, what I do is amateur by comparison. But, I wasn't about to let the Red Hulk beat me. So I persevered, and with blood, sweat and profanity I successfully converted the Centurion to a direct plunger format.

Firstly, I figured out how to add two springs to the reverse plunger layout. This made the blaster horribly inconvenient to use because the extra two spring (on the back of the plunger) would force the breech closed. Making loading a nuisance. You would have to hold the breech open to load a clip and found that the blaster would try to double load often. The best performance I got from this was 95 feet. Majority of the darts would spin into the ground and the only way the shots could be less accurate would be if the darts shot out of the shoulder stock when I pulled the trigger.

I had also removed the AR and the all the nanny locks then added a second trigger catch spring. The main problem I had with this blaster was ensuring the extra springs stayed in one place as the blaster primed, I solved this but adding a shaft to the end of the plunger tube with a short length of tube in the spring seating to keep everything in place. This worked well in the sense that it did its job. I also worked on the barrel locks to make it removable. Some fishing line holds the dart chamber to the "bolt sled" allowing the chamber to move with the priming handles in both directions.

The result was a noisy, jarring, inconvenient mess of springs and plastic that was less useable than the Centurion in its original layout!

So, I decided to un-mod the Centy simply because it was dangerous in the way I modded it and the kids like playing with it.

Suddenly, a wild light bulb appears...

Now direct plunger conversions have been done before, PsykSG did one, but he also converted the blaster to take regular Elite darts. He also gutted the Centy and replaced the internals, the only Centurion part left was the shell. I wanted the Centy to fire Mega darts. It's a Mega blaster and I want it to fire Mega darts.

I played with several ideas for a PT (plunger tube) replacement, I eventually settled for a women's deodorant can because they are usually long and about the right diameter. I was at K-Mart and found some Hello Kitty deodorant (Vanilla Ice-Cream scented if you want to know). I was excited to learn the diameter was perfect and being metal it would be sturdy too. I used a brick to hold down the button and in about 2 minutes the can was empty. the I poked a pin hole in the top to vent any residual pressure. The I sat the dart chamber end of the PT in some boiling water and gently pried off the end cap. I then cut the "inner-tube" that connects the plunger head and the dart chamber. I cut it at the same height as the end cap and filled the dead space with hot glue. I also removed the rod connecting the chamber and the plunger head.

I used a hacksaw to remove the top and bottom of the can. I didn't use any tool that might've created sparks incase there was any flammable fumes left over. Then I rinsed the tube to remove any residue. I flanged out the end of the can and it fit onto the AR housing nicely. I didn't have any O-rings beg enough for the plunger head so I made my own seal out of craft foam and hot-glued the foam onto the plunger head. The air seal was perfect! I did some tests with the dart chamber attached. I held the plunger tube with one hand and slammed the plunger with the other and the results were promising. When I checked the length of the can-tube though, it was too short. In hindsight, I should've checked the length first.

Removing the Hello Kitty plunger tube was easy enough. but then I was confronted with the issue of not having a PT at all now. Then I realised the answer was sitting in front of me the whole time. There are two things wrong with the Centy's PT. The tapered bit and the slots. The slots where easy to plug up (properly). I wiped out the inside of the PT with a rag and used duct tape to cover the slots from the inside. Then I filled up the slots with hot glue from the outside. Once it was cooled, I trimmed the excess glue off to make it flush with the side of the PT and removed the tape. Then the tapered end. I don't have a drill bit big enough to do this nor was I about to buy one just for this one job. I have a metal 30cm ruler with sharpish edges and used that to shave the inside of the tapered end of the PT until the amount of resistance on the plunger head was tolerable. This was a slow process.

I used hot glue to plug any air leaks I could find and lubed up the inside of the PT liberally and inserted the plunger. I reattached the dart chamber to the AR housing and used rubber cement to improve the seal. I cleaned up the rod on the back end of the plunger tube (originally a stick) to a length of 16mm dowel tapered at one end to allow easy insertion into the orange barrel guide. It is a perfect fit but I still sanded the dowel to make it glide through the guide with ease.

When this was firing the plunger was hitting hard, that's because the end cap attached to the plunger was hitting the PT itself. I remedied this with a ring of black foam that pads it nicely. For this layout to work, the priming direction of the handles needed to be reversed which wasn't hard. I can now calibrate the gearbox easily thanks to my experience with it in the triple spring mod. I still prefer not to though.

Someone else might find a good sized bit of PVC to make a PT out of but I'm happy with it as is for now. The hard work has been done the rest is just tweaking now. I'm still on the hunt for some good barrel material though but 90 minutes at the hardware store returned nothing, so the outlook it not so good :(

Does this mod make a Centurion more attractive to you?

~ Rob


  1. How much was the range/sound/firing etc improved?

  2. Rob, I would look at Aluminium tubing for barrels, they make lots of sizes and it telescopes like brass if you choose the correct wall thickness.


Related Posts Plugin for WordPress, Blogger...