NPAS for Open Bolt WE Scar
 

Has anyone come across a good YouTube video on how to install the NPAS in an OB Scar. I found a pictorial write-up and it references cutting something off the valve spring but its not clear on exactly what to cut. I'm thinking that its the little curly tail on the end of the spring. Can anyone confirm this? Also, the pictorial says not to trim the prongs but other sources say to trim. I believe that trimming the prongs is supposed to allow extra space for the new valve to move within to increase the range of fps settings. Anyone know for sure whether the tabs have to be cut and how much? A good video would really help. Anyone who has done the conversion interested in walking us noobs through it? Thanks for any help. Link to pictorial instructions below. Sorry, not sure if this will end up being an active link or just text but I suppose you can copy and paste into browser window.

http://forums.zeroin.co.uk/showthrea...28open-bolt%29

You don't even actually need to cut it, that's just so you can adjust it without taking the whole thing appart. But yeah, don't take any loops off, you just need the path between the spring clear, so your tool can get to the adjustment screw on the NPAS.

In reality, I think the NPAS is crap, and if you want less FPS AND improved gas efficiency (which the NPAS won't giva ya), I recommend switching the floating valve spring (the spring you wanna cut). Most TM compatible pistol floating valve springs will do the trick.

What FPS do you want/need your gun shooting at?


Fox.

Thanks Fox. The gun is shooting about 460. I need it to shoot at the typical range limits of 350 or 400. I'm a little new to this (you may have guessed) so not sure what you mean by "TM compatible pistol floating valve spring". I thought this was the only way to adjust the fps of GBBR's. Looking to do what works best. So any input is greatly appreciated. So, just to be clear, in the photo of the spring there is the little curly tail at the end of the spring. That is what needs to be nipped off but it is just so the tool can get in. If the little tail is not in the way of the opening then it doesn't need to be cut? What about the shaving of the lugs on. Also, if you want to elaborate the method you mentioned I'm very interested. What do you mean by "increasing gas efficiency"? Man, this is a great place to learn.

The "float valve" and "floating valve spring" are these bits
http://tapatalk.com/mu/6d9c850e-6811-1a6e.jpg

They are very, very similar to what's used in a lot of gas blow back pistols. It's the NPAS (negative pressure adjustment system) airsoft wizard magic that makes these things work. There's a great informational writeup somewhere on Redwolf...and the link is somewhere in the forum.

In short...this spring/valve controls where the gas from the mag goes. If the valve is open, the gas goes down the barrel (pushing the BB). If the valve closes, the gas pressure is trapped and the nozzle (plastic black housing that you stuff all this into) expands and drives the bolt back. Cool...

By altering the weight of the valve, the stiffness of the spring and how close/far the valve sits relative to its closed position....you can alter the FPS of the BB. Essentially you're fiddling with the timing and choking off the system.

The RA NPAS allows you to adjust the FPS without taking the whole thing apart over and over by sticking a "screwdriver" down the tip of the nozzle to lengthen/shorten the floatvalve, making it sit closer/further away from its closed position. To do so...if there's a bent "leg" on the float valve spring (and there is on many of them)...you typically nip it off so you can get your adjustment tool down the nozzle.

The lugs are there to stand the base of the float valve off of the nozzle body. As long as gas can get behind the valve to push it forward...you're good. Also...as long as there's physically room in the nozzle for the float valve (and shaving the nubs would make more room) you're good.

Re. gas efficiency...I think that he's relating things to the weight of the valve. The heavier the valve, the "slower" it moves and the more gas that is wasted. You can alter the timing by changing the spring tension. However, it's trial and error and does not allow for any adjustments for temperature.

As temp goes up, so does the FPS of your gas rifle. You need to be aware of that and it's up to you to stay in check with your game limits...adjusting as need be.

Thanks m102404. That is a great explanation. Understanding the theory behind this makes it much easier to understand and the procedure makes sense. I lover tinkering and one of the things I am really looking forward to is tinkering and modding the guns. But, by the same token I don't want to break anything on these very expensive "toys" and be worse off than when I started. This is a great community and a great source for information. Thanks so much for your time. I'm sure others will get a lot out of this as well.

Yeah, that's a very good explanation.

I run a very custom SCAR, and I've tried most of the stuff out there for it; I again didn't find the NPAS to my liking. But try it, if it gets ya where you want consistently, you're good to go.

Be careful though, since you will want to change your bucking (hop up rubber), and the air seal on the stock one is horrible, we're talking a 60-90 FPS difference from that one to the Falcon, Nine Ball, or Modify. Although it might be different since you have the Canadian version of the gun, and not sure what tweaks WE made on those to get 'em shooting that hot OOtB.


Fox.

Not sure of what they did inside but they added an extended barrel with a suppressor on it for looks. Pretty sure that reverting back to standard barrel, which came in the box as well, would probably cut the MV by 20 to 30 fps. Once I get it apart to do the NPAS I will check out the hop up. I read somewhere, think it was this thread, that adding teflon tape improved the air seal. Is that a good idea or do you see that coming loose and getting jammed in the works?

I used to do that, but it really doesn't work well enough, or forever to warrant doing it. It might not even improve FPS at all with a good bucking.

Get the Falcon open bolt bucking (clear). Great air seal and accuracy, and quite cheap. Might want to give the Modify VSR-10 bucking a shot, too.


Fox.

Thank you for the continued input. Are there any other reasonable upgrades that I should consider doing now (while doing the NPAS) and while I have the gun open (not to say it can't be opened again) but stuff I could be doing like Fox's suggestion about the bucking. What about part 027? I understand it is a common failure. RATech has a replacement part at about $70. Is it worth doing now? If the stock one fails, what are the possible repercussions?

If you have the money and want a pretty much "Workhorse AEG"-reliable gun, you gotta get the following:

- TSC Part #66
- RA-TECH Part #27
- GunsModify full Steel Bolt set
- RA-TECH full steel triggerset
- Whatever aftermarket inner/bucking combination suits your needs.
- Use the WE VN Style M16 GAS (never use CO2 on this gun, it's CRAP) mags, which are more consistent, gas efficient, reliable, less prone to leaks and hold more gas.
- Properly grease the gun and oil the mags

That amounts to TONS of research and trial n' error.


Fox.

Wow. Lots to think about. I have part 66 and 27 on order. I also went with the Modify VSR hop up. Will probably change out the internals as I grow more confident with my gun smithing abilities. Thank you all for your help.

got a question, how do you guys fix the double feeding issue of the open bolt system?

For me it was stretching the recoil spring so the bolt didnt bounce back and pick up a second bb.

Gen 2 M4/M16/SCAR/PDW magazine soon gents.

http://airsoftbuddy.com/member/52976/eshop/IMG_8220.JPG
http://airsoftbuddy.com/member/52976/eshop/IMG_8224.JPG
http://airsoftbuddy.com/member/52976/eshop/IMG_8230.JPG

From AirsoftBuddy.

Less leaks?