Southern Brisbane Nerf Club

Tuesday, 3 September 2013

MEGA Centurion, an epic quest for knowledge

Esteemed members of the NIC. I come before you today, a broken man. I ventured on a journey of enlightenment, of knowledge, of modification. My quest begins, in the barren red wastelands of the Centurion and ends with the realisation of a horrible truth!

I set forth on my epic journey not knowing what peril lies ahead, all I knew was, this is something I must do.

Before entering the wastelands, I was confronted with the thirty warriors guarding it's boarders (the screws). They were no match for my might! Then I went toe to toe with the mighty titan himself... The barrel extension. A harrowing battle that seemed to last an age. As evenly matched as we were, I emerged victorious, but not without injury.

Once the titan had fallen, the gates to the temple opened. Oh the wonders that lay within. I set straight to work removing the barrel locks. Only to discover that there were barrel locks in the barrel itself, they too, were easily defeated.

Deeper I ventured, to the plunger, located in uncharted catacombs. It was difficult to remove but not impossible. The guardians of Air Restrictor (3 screws) fell with little effort. And then, there it was. The Air Restrictor. Bigger than any before it but easy to remove.

Now. The plunger. The centre of many a story. Upon inspection, I found it to be sealed shut (acetone glued). And then, the vents. Four slots cut into the side of the plunger tube, I gazed into the abyss, and saw what appeared to be a Longhshot sized spring. The inner tube of half the diameter of the outer tube, this allows room for the internally mounted spring, but it also meant, there was room for one more... this was my goal!

I searched the perimeter for a way in, but none could be found. The vents, too small for any man. But I'd come this far, I've fought and bled for this moment. How can I turn back now when I'm so close to my goal! I must see, I must know, what is inside! Hacksaw in hand, I contemplate what I'm about do. Do I potentially destroy this blaster in the search of knowledge? In the Search of modification?

"Yes" I say to myself, carefully I start cutting and before long, it opens. And there in all it's glory, was the plunger. The source of the Centurion's power! I was amazed at the fact that the plunger head made a perfect seal against the inner side of the plunger tube. The internal spring was undoubtedly a method employed to prevent spring replacement. Inside the inner tube, I noticed a rod connecting the plunger head and the AR mount at the other end. I removed the screws in each, but alas, more acetone.

I was soon to discover, the true horror that lay within the bowels of the Centurion.

I turned my attention to the vents in the tube, surely, plugging them would improve performance? I drew the plunger back to where the vents are and something caught my attention that I didn't notice before. The O ring, didn't seem to be pressed as hard against the inner side of the plunger as it was in it's resting position. I looked into the plunger tube through the hole I made and then realised the horrible truth.


What does that mean? It means that the internal diameter of the tube is wider near the dart chamber than it is at the resting spot for the plunger. So plugging up the vents will not improve performance, in fact, plugging them might decrease performance (I'll explain later). I've observed the plunger head as I moved it up and down the tube and have ascertained that the "compression zone" is only 25mm (one inch) in length at the bottom end of the plunger. This was discovered to be true with some testing after I had put the plunger tube back together. I plugged the vents temporarily with some play-dough and aluminium tape, and found that the resistance from the compressed air started when the plunger was in the same position as when it wasn't plugged.

At the front end of the plunger tube, where the inner tube enters, there are some air holes, but the holes can't be plugged because of where they are positioned. These air holes are part of the entrance hole for the inner tube. So plugging them would increase the friction on the inner tube.

Why the vents then? Why would plugging them decrease performance? Well, it's all to do with fluid dynamics and how the plunger compresses air.

With a normal plunger, the air starts to be compressed as soon as the plunger starts accelerating and before the plunger is going as fast as it could be, the dart has left the chamber and the AR does it's thing. But with the Centurion, the air is being compressed when the plunger is going as fast has it can go, giving the MEGA dart a decent punch of air to launch it. This is why the Centurion has the padding inside, there is not enough time for the AR to do it's thing. The AR is there to protect the blaster from dry-firing more than to reduce the air delivered to the dart. However, removing the AR would reduce the resistance the air experiences on it's way to the dart.

To make sure the plunger head is going as fast as it can when it gets to the compression zone, the air resistance needs to be reduced. This is what the vents in the tube are for, to vent any prematurely compressed air or turbulent air from the tube, reducing the air resistance on the plunger and thus ensuring the head hits the compression zone AFAP (As Fast As Possible). The tube tapers out towards the AR end to reduce drag. Blocking the air holes or the vents would increase the air resistance the plunger head experiences, slowing it down on it's way to the compression zone. Thus, reducing range slightly. However, there have been reports of range increases with plugging the vents, but, I'll leave it to you whether to do it or not.

So, the Centurion, effectively has a 25mm plunger tube. And without making your own, it's the one you're stuck with. There are direct plunger, brass breech kits available that will fire Elite darts, but, what you're really doing is turning it into a Longshot with a brass beech aren't you? It would only be a Centurion in appearance. If that were the case then, why buy a Centurion at all?

~ Rob

1 comment:

  1. That would explain why i only gained a few metres range after plugging the PT. Time to open it back up then. Thanks for doing this, i wasnt going to cut open a US version, but i'm glad you sacrificed one.


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