Should I use a piston cup or an O-ring config?

[Matthias]

Well, I am considering getting an EdGi upgrade piston for my BAR 10 but his uses a piston cup like the aps 2 and I was just wondering if this was inferior to the O ring design that TM uses, also, it does not come with an airbrake, so which would be the better choice? I tried searching but there doesnt seem to be anything addressing this.

[Stealthbomber]

A cup seal will always offer a better seal than an O-ring.

 

On the down side, however, the edges of the cup seal will catch on any holes in the cyclinder and wear quickly. If you have any cylinder vents then it's probably wiser to go with an O-ring.

 

Bit random but I tried fitting an air-brake on my L96 and found I couldn't really get it to make much difference.

I built one for an AEG and it worked very well (so well that I got rid of it because the gun sounded like an electric drill!) so you can assume I was doing it right.

 

I think the reason the air-brake wasn't as useful was because, at the higher power, the brake was stopping air venting out the nozzle so, instead, it was forcing its way past the O-ring and so the piston still wasn't slowing down.

Maybe a new O-ring or different piston head would solve the problem but, I dunno, I kinda like the muzzle crack so I decided to leave it alone.

[Matthias]

Care to tell me how you made the one for the AEG?

[Stealthbomber]

Care to tell me how you made the one for the AEG?

<{POST_SNAPBACK}>

As per the instructions on the Daedalus Devgru website. Can't recall the URL.

 

Basically, you smash up a VHS tape and steal the small teflon roller that will fall out.

You then drill a 3.5mm hole right through your piston head and countersink as well.

Slide a 15mm (or thereabouts) M3 screw through the piston, from the back (difficult) and put a nut onto the front of the piston.

The nut should tighten down into the countersunk area when you tighten the screw leaving you with a normal looking piston and head with about 10mm of M3 thread sticking out the front.

 

You now need to thread the teflon roller from the VHS tape M3.

Do this either with a tap or by screwing an M3 screw into in.

Now cut the head off the M3 screw, stick it in an electric drill, attach the roller to it, and (with the drill running) use wet & dry to taper the roller so it fits neatly into the hole in your cylinder head.

 

You will also need to cut the roller down to a suitable length of maybe 10mm

 

This is the key part. Too tight and it'll jam. Too loose and it won't work. Too long and it'll cause the gun to lose power. Too short and it won't work. This can take several goes to get right and create a pile of smashed VHS tapes.

 

Once you've got the roller tapered so it fits the cylinder head, unscrew it from the drill and screw it onto the front of your piston.

 

You're done.

 

The idea is that, when the gun fires, the piston cannot slam into the cylinder head any more.

Instead, the air-brake plugs the hole in the cylinder head and the piston is cushioned by the air remaining in front of the cylinder. Because the seal isn't perfect this air will leak away in a fraction of a second and the piston will complete it's travel, but won't slam into the cylinder head like it used to.

 

That's the theory.

Like I say, I couldn't get it to work on the L96. Not sure why but, as I said, I suspect it was plugging the cylinder head and the air was squeezing past the O-ring instead.

Must admit, I can't recall if I ported the piston on my L96 so maybe it'd work with a ported piston.