KJW CO2 Magazines: FPS Lower than Green Gas

[Algy]

Hey there, I'm currently experiencing a problem with my KJW 1911/MEU CO2 magazines (who isn't?). As the title suggests my CO2 magazines are somewhat underpowered compared to the gas magazines I have.

I am using .25g bbs and have found that the gas magazines shoot between 275-280fps, whereas the CO2 magazines are only putting out around 210-230fps. The blow-back of the CO2 is much more powerful, so I don't doubt that enough CO2 is being released in sufficient quantities, but it would seem that the bb is receiving less pressure than it should.

Could this be something to do with the floating valve closing too soon? Any other ideas/solutions would be greatly appreciated.

[NonEx]

Yeah, probably the force of the CO2 closes off the floating valve early as mentioned. Try taking out the floating valve and stretch the spring a little bit to make it harder to close. Or remove material on the floating valve piece itself, from the rear.

 

Strange though as that model should be ready to go on CO2. I haven't chronoed mine though so maybe it's the same for mine.

[Algy]

If I stretched out the floating valve spring do you think I would see a drop in fps when using the gas magazines?

Also, my MEU is the red nozzle version, so CO2 is fine, though I have put a few thousand bbs through it.

[NonEx]

I can't say, it should be the oposite though, if the spring is harder, the valve closes later, more gas on the BB should mean more FPS.

[Korppi]

The meu should shoot something around 325fps (~1J with 0.2g bb) with co2 mags. Installing a magazine shim (Lees Precision Engineering) could/would boost the fps closer to 1,3J.

 

Do you have several mags with all the same problem? Are they the new or old profile mags?

[Algy]

So I think the problem has been solved. As NonEx suggested, I stretched out the floating-valve spring a little and the fps jumped from around the 220fps mark to 300-320fps (on CO2). Gas consumption seems to have gone up a bit, but I think the spring will settle again soon, so that should remedy itself.

Thanks for the advice NonEx, much obliged.

 

@Korppi: Yeah it was all the CO2 mags (old style), and I had already installed magazine shims. I'm starting to think that CO2/Green Gas pistols aren't such a great idea, as the two gases behave so differently it's difficult for one pistol to properly accommodate both.

[NonEx]

I think this is the first time I got something right with GBB troubleshooting, yay for me !

 

Glad it worked!

 

Out of curiousity, what happened to the green gas FPS ?

[Algy]

When using the gas magazines the first shot comes out at about 290-300fps (using 2.5g), but the last shot (can get around 18 shots out of one fill now) is around 265fps. I imagine that as the floating-valve spring compresses over time, this will go down again which is a good thing because I suspect I over-streched the spring a little.

 

The thing is, had I never chronographed the pistol I wouldn't have known there was a problem, when I take the pistol to skirmishes the pistol perform pretty well even with the low fps that using the CO2 magazines caused. Over shorter ranges (the pistol is my secondary) I suppose fps makes less of a noticeable difference, but still it was really bugging me because it shooting so low clearly wasn't right. Thanks again NonEx, now I know who to pester if I have any more problems!

 

@Korppi: Thanks for letting me know what the CO2 fps should have been, I looked around on the internet a bit and got a few different figures, and yours fits in the middle, so would seem accurate.