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Rocket Valve O-ring Mod

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#1 failsmith

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Posted 09 December 2013 - 05:25 PM

WHAT: This is a guide on how to increase your GBB's efficiency in about ten minutes for very little money. I've seen other guides on other forums about this mod, but I haven't seen any here.
The idea is to disassemble the replica, add a small o-ring around the rocket valve, and re-assemble.

WHY: The o-ring helps provide a better seal between the rocket valve and the inside of the nozzle, so that less of the gas is wasted on each shot. This mod provides a crisper, more powerful blowback*,  better efficiency*, and possibly better FPS*.
(*Working on getting a chronograph to test these hypotheses and get real concrete data. Results of these tests will be posted in a follow up post to this one.)

HOW: Here is a step-by-step walkthrough of how to do the mod. I'll be using my USP (NS2 version), but I believe this will work on other GBB's as well (I haven't tried it in any other models, so I can't guarantee this).
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First remove your magazine, pull back the slide and make sure there is no bb in the barrel, and all that good safety stuff. Remove the slide from the lower receiver. (I'm assuming you know how to disassemble your replica. There are many guides on youtube and on this forum for each individual replica, look for one of those if you're having trouble. http://www.kwausa.co...p?showtopic=575)
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Remove the barrel/outer barrel/ hop-up unit, and the return spring and spring guide.
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Unscrew the blowback unit from the slide. (You'll see a flathead screw here, but yours may be an allen key bolt, I replaced the screw on mine.) you may need to gently pry the BBU up away from the slide to get it out.
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The nozzle is held in place by two small springs. Pop one end off of each spring, and remove the nozzle from the rest of the BBU
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Inside the nozzle is the rocket valve, a small silver colored piece held in place by a stud.Posted Image Use a small allen key to push the stud through the other side. (Watch for the rocket valve, it may pop out.)
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Now, take a #5 danco o-ring, which can be purchased at home depot in the plumbing section.
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Put it around the end of the rocket valve.
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Place the valve, with o-ring, back inside the nozzle, being careful that the skinny end of the rocket valve ends up inside the spring.
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Now use a small screwdriver or something to hold the rocket valve back inside the nozzle so you can replace the stud you pushed out earlier. (I don't have a picture for this step, this part is tricky to photograph.)

Reassemble the blowback unit, replace the screw (sometimes it can be hard to line the rear sight up correctly). Replace the barrel/hop unit/return spring assembly in the slide, and place the slide back on to the lower receiver.

Fill a mag with gas and test her out!

From what I can tell it seems like I'm getting better blowback, and more shots out of a magazine.
In my next post, I'll do a side by side comparison, measuring shots per magazine and FPS, with and without the o-ring installed. I'll post all my data so I can actually measure the increase in efficiency.

If you decide to try this, post your results! It would be nice to have a collection of concrete data gathered from different people using different set-ups to see how it works out.
Good luck!
-Failsmith

#2 failsmith

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Posted 10 December 2013 - 08:56 AM

Currently getting 40-45 shots out of one magazine in 38 degree weather with a swollen bucking. New bucking is in the mail, will do a proper test once it's installed. Haven't removed the o-ring to test fire, but I remember having trouble firing all 25 bb's in weather like this.

#3 SR105

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Posted 13 December 2013 - 05:15 PM

Any difference in the FPS after the mod?

#4 gcw360

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Posted 13 December 2013 - 05:47 PM

View PostSR105, on 13 December 2013 - 05:15 PM, said:

Any difference in the FPS after the mod?
I'm thinking it might have gone up.  Why, because it compresses the spring to add tension.  Just a guess though.





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