Compression Confusion - Any Ideas?

[E30Adam]

Can anyone shed any light on this please?

V2 gearbox shooting 370fps. When I dismantled it to shim, I removed the piston and cylinder assembly. When I put my finger over the cylinder head nozzle (air nozzle removed) and pushed the piston in, there was no resistance at all which told me the compression was poor. So.. I stripped the gun again and switched out the O-ring on the piston head for a better one. I performed the same test blocking the cylinder head nozzle with my finger and pushing the cylinder in. This time, superb compression, no air leaks and a very solid feel to the piston.

So my thoughts are that better compression should be a more efficient system and more power?? Wrong, I lost 40fps, the gun was now shooting 330fps. Nothing else changed at all and when I swapped the o-ring back, it chrono'd at 370 again.

Can anyone explain this because it makes no sense to me, am I missing something here?

Thanks in advance.

[RitchieTheBrit]

Re: Compression Confusion - Any Ideas?

Did you push the piston home quickly? Not sure how much you know about the inner workings, but the piston expands outward as air is forced into the bleed holes, creating a tight seal against the cylinder.

A lightly lubricated o-ring with good expansion performs better than an over-snug o-ring in my experience.

I found that stretching an o-ring across an old cylinder, gently heating it with a hair drier while intermittently applying silicone oil works wonders, especially for new rings. I think the combination of stretching it and oiling then heating it creates larger pores in the material that the oil can sent soak into, leaving it softer and more pliable. I'll give it one last dose of oil, and leave it overnight on the cylinder. Then simply regrease and refit.

[E30Adam]

Re: Compression Confusion - Any Ideas?

Cheers Ritchie!!

I know a fair bit about the workings and I realised the vents expand the O-ring. There didn't seem to be any compression even when pushing the piston in quickly. The gun shoots beautifully with the original o-ring, I was just interested to learn what was happening here. Perhaps the newer O-ring was a bit too snug. I'll try stretching, heating and applying the silicone oil as you suggest.

Thanks for your input :-)

[RitchieTheBrit]

Re: Compression Confusion - Any Ideas?

It could be, does the new ring have good compression when you slowly slide it in? It's a bit strange, because sometimes o-rings defy common logic!

When I started tinkering, I thought that a ring with good compression when slowly slid to battery would be more effective than a slightly loose one, but that's not always the case ha!

[Figjam]

Re: Compression Confusion - Any Ideas?

What happens to the FPS when you put the old o-ring back in?

[jonny lovegrove]

Re: Compression Confusion - Any Ideas?

What happens to the FPS when you put the old o-ring back in?

Nothing else changed at all and when I swapped the o-ring back, it chrono'd at 370 again.

[E30Adam]

Re: Compression Confusion - Any Ideas?

Yeah the new ring has fantastic compression weather pushing the cylinder in slowly or quickly. It certainly seems to defy logic.

Yeah when I put the original o-ring back in, the fps returned to 370

[Figjam]

Re: Compression Confusion - Any Ideas?

Thanks Jonny. Derp moment there.

So yeah, if the old 0-ring gives you better FPS, then there is a problem with the new one. My guess would be that by being so tight, it actually resists the spring. Possible trouble arising from this would have to include at the top of the list a risk of pre-engagement.

[RitchieTheBrit]

Re: Compression Confusion - Any Ideas?

Figjam is totally correct. Did you apply any kind of lubricant?

[E30Adam]

Re: Compression Confusion - Any Ideas?

Yeah I gave it a good covering of silicone lube.

[RitchieTheBrit]

Re: Compression Confusion - Any Ideas?

Was it a squeeze getting it into the cylinder?

All this talk of lube and squeezing in... We could publish these threads. The 50 Shades fan girls eat this stuff up!

[E30Adam]

Re: Compression Confusion - Any Ideas?

No, not at all. The cylinder moved pretty freely too, no noticeable resistance. I couldn't figure it out because it defies logic so I just swapped back to the old o-ring and put it down to being a mystery. It bugs me not knowing the reasons for what happened.

A friend of mine said the compression might be too good, therefore creating a back pressure so the spring has a harder time pushing the cylinder forward which kinda makes sense. He's not from an Airsoft background, just his thoughts on the matter!

[dave38x]

Re: Compression Confusion - Any Ideas?

A friend of mine said the compression might be too good, therefore creating a back pressure so the spring has a harder time pushing the cylinder forward which kinda makes sense. He's not from an Airsoft background, just his thoughts on the matter!

Doesn't make sense at all! The higher the pressure in the cylinder, the higher the FPS, simples The only time this sort of "back pressure" occurs (when really it's just the air not being displaced out of the cylinder resulting in the pressure of the gas in the cylinder and the load exerted by the spring achieving equilibrium) is when you have a jam and a BB is stuck in the hop unit.