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Increasing Gas Gun Performance with Acetone?!?


renegadecow

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Ever get gummy o-rings? Somehow your valves don't open as quick and you get sluggish shots? Ever have o-rings dislodge/come unseated even after just replacing them with better ones?

The o-rings you find in gas guns be it NBB or GBB are more often than not made of Buna-N (aka nitrile) with a 70 durometer (hardness). Now for whatever reason like age or relative temperature these o-rings can soften up leading to malfunctions mentioned above. Up until now my only recourse in fixing them would be outright replacing them. Using a higher durometer would probably mean getting rid of said problem forever, but sometimes it's not easy finding 90 durometer of the size you need, especially in small quantities. So I set out in finding a way to harden o-rings just enough so they'll be usable again and perhaps even improve on their performance. Sound like I'm selling Viagra? I'm sure Fireknife thinks so.

 

Now for the science part. There's really only one way to make an o-ring harder and that is to reduce the mount of elastomers it has. But that is usually dictated from when the o-rings are being made in its primordial goo state, not when they're already formed and possibly used in your gun. Extreme heat can be used to evaporate some of the elastomers out of a formed o-ring, but will almost always mean damaging the surface of the material which would lead to leaks. So I figured why not dissolve the elastomers out of them?

Buna-N is one of the most used types of o-rings because of their resistance to a wide range of chemicals. For that reason they're used in our gas guns which are powered by HFC134a, propane, HPA or CO2. One such chemical they are not compatible with is acetone. It will literally eat up Buna-N. So why am I suggesting it as a fix? It's all in the time of exposure.

Leave an o-ring in a tub of acetone and you probably won't find it there anymore a couple hours later. 30 minutes and it will bloat up like noodles with cracks all over the surface. 5 minutes and it would soak up the acetone and release some of its elastomers through osmosis. Magic!

 

The procedure:

Find a small container that can withstand acetone and can fit your o-ring (I used the plastic container for camera film). Put in as much acetone (mines 80% nail polish remover) as you need to completely immerse the o-rings (about 1/4 to 1/2 full for 1-5 small o-rings). Put in your o-rings, replace the cap and swish the contents around a bit then leave for 5 minutes. Do not leave them for more than 10 as they will be completely ruined. After the elapsed time, open your container and fish out the o-rings and let dry. At this point they will still be bloated out some 15-20% in volume having still soaked the acetone. It will take about 30 minutes to an hour before they shrink back down to original size. But the difference now is that they've lost some of their elastomers while in the solution and are slightly harder.

Other than fixing my guns which have had o-rings dislodge, I find that they also slightly improve the output on guns that are still working. As some of you may not know, when it comes to gas guns the power output is dictated by the speed of the valve opening and its volume to allow flow. On a gummier o-ring, as the valve begins to open from being pushed by knocker/hammer the pressure of the gas pushing against the valve will want to keep it closed. It deforms a little enough to keep a seal until the valve has opened wide enough that the elasticity of the o-ring can't hold it closed anymore and it opens fully. With a harder o-ring, the valve opens more readily as there is less flex on the o-ring to keep it closed.

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