unusual fps from upgraded spring
 

I have a full metal d-boys stock m4 bushmaster stlye AEG. The gun is shooting around 340 fps stock. Today I tried a variety of springs to increase the fps as well as some other little hop ups.

First off I tried a modify s120 spring which i have read to produce around 400 fps. Installed it cronied at 320 fps.
Next I tried another 400 fps spring, same thing around 325 fps. I was thinking i must have done something wrong so i went back to the stock spring and nope, back to 350 fps. The modify s120 is at least one inch longer than the stock spring. I dont know if this matters but i really thought it would put it up to 400fps. I tried a new piston, head, sleeve and that made things worse. Now the nozzle protruded slighly into the hop up and stoped ammo from feeding properly. I have had this box apart about 10 times now and I am feeling dumb as to why with upgraded parts it performs worse. Maybe D-boys just have shitty mechboxs that dont like upgrades.

Any suggestions?
Is the mechbox worth upgrading or should I just build a new one from scratch?
Anyone have a recomendation for a good drop in mech box around 400fps.

Thanks:)

That's really twisted about the weird FPS'. Chrony's ok? Didn't load 0.25's by accident?

Is it a ported cylinder? If it's a full cylinder, the bb might be gone before it reaches top speed.

Of if you have a really long barrel on it...it might not be long enough without a full cylinder...

Stuff like that.

It's ok if the nozzle protrudes a bit, as long as it retracts a bit more before it goes forward...check that it hasn't jumpped off of the tappet plate. A full disassemble and reassemble might change it a hair. Tighten the stock screw.

Or...do what I do now...buy a G&P complete mechbox and just reshim it...LOL!

bad airseal?

hey George....are you maybe putting the upgrade springs in backwards? Modify springs aren't linear so there is a front and back....

the end with the more coils at the rear (seating on the spring guide)

Bad airseal or incorrect cylinder porting. Stronger spring is pushing piston faster but air escaping out cylinder port instead of through nozzle?

thanks guys i think i am going to put it back to stock and keep it as a back up mech box. I am just going to try a couple more things. This problem has frustrated me for 2 days now. thanks for the tips i will try them out and report back.

by just upgrading the spring can air escape out the cylinder port when firing?
how would you solve this. take a tooth off the piston or block part of the port?

Friend of mine had the same problem on his VFC HK 416, and couldn't figure out why he had such a low FPS. He had just replaced his stock spring with a new 1J one, but it would only give him about +-280 FPS. I had him do the timings differently (correctly), and he got 330+ You should try and check this. I know some people don't believe in timing of gears, and some supposedly even proved that gears reset themselves, but this is not the case with any of my 3 gearboxes or my friend's one. You see, it's all about when the nozzle is let forward into it's foremost position and seals up with the hop-up rubber sleeve. At the same moment the piston is released and it starts moving air. Well this is what's supposed to happen, and it didn't happen on my friend's v2 gearbox, or my own v6, without proper timing that is!

Also, for or better airseal between hop-up rubber and the nozzle, get an o-ring (of the proper size) and thread it over the inner barrel, all the way to the hop-up unit. It might be a tight fit, so don't use too thick an o-ring! This will help press the hop-up unit more tightly towards the gearbox, hence giving you a better airseal between nozzle and hop-up rubber.

EDIT: Guys, I'm pretty sure he didn't say anything about swapping inner barrel or cylinder, only the spring. This would mean that the porting should be ok. As long as the spring is placed the right way around, it should be ok. That's if it's an irregular pitch spring!

a dboys spring in my custom G&P mechbox output enough eK to go through the side-bottom of a pop-can. And the dboys nozzle doesn't seal. it makes air gush out the bottom. actually, neither does the piston head. yeah... get a modify cylinder set is all I can recommend really... also the DBoys spring is really really short and very strong, which is how it achieves such high fps. Most springs are about an inch longer.

Poor man's chrono is not really to be trusted, but can give you hints about the speed.

The airseal problem isn't due to to nozzle itself, but because the v2 hop-ups rarely provides enough pressure against the gearbox to provide good enough airseal between the nozzle and hop-up rubber sleeve.

The piston head isn't supposed to provide the airseal (between the cylinder and piston head), but the o-ring on it is. Simply getting a better o-ring for the pistonhead, or maybe an x-ring can make a huge difference.

the pop-can thing is accurate to about +/- 30-40 fps, either way, it's much higher than what he's getting. Also, a bad air nozzle will have a big effect because of the amount of air escaping the bottom of the nozzle. An o-ring nozzle should cure the problem. The nozzle opening also is responsible for making a seal around the BB to propel it. A hop-up spring that is slightly too weak shouldn't create such a big problem. Because the spring is still there, it pushes the hop-up unit against the mechbox with sufficient force. Well, most springs do anyways. If not, it can always be streched out slightly.

uhh the pop can is in accurate. if you put a hole in it its about 300+ fps any other test is basicaly useless. someone did the 400 fps test with a 330 fps gun and completed the test successfuly.

Just stop right now. There is NO such thing as gear timing.

O.o... for the can test most of mine came in the 30fps range... But then again I always use new pepsi cans with .2g BBs. Although the confirmation chronoing is done at a game probably under different conditions.
gear timing doesn't exist. Think about it, the tab to pull back the tappet is attached to a specific spot on the sector gear. so when the sector gear turns a full cycle, so does that tab, it's completely irrelevant to the position of the other 2 gears.

POP can chrony is useless and will never give you an accurate FPS.

Gear timing is a myth.

Your problem lies with air sealing. Maybe D-Boys mech boxes have an issue with air sealing and they compensate with a stronger stock spring in comparison to let's say TM? I would take the D-Boys spring and put it into a TM mech box and see what FPS it gives. You may find that the D-Boys spring in a TM will give you over 400 FPS.

Just a theory, as I have no experience with D-Boys, however I have plenty of experience overall.

Pop can chrony = bad
Gear timing = just plain wrong (sorry, no personal offense meant)

If the AEG reliably shoots 330 with one spring and there aren't wild deviations between shots...then simply dropping in a stiff spring should result in a higher velocity.

Things that mess with this are:
1. You screw something up with the previously good airseal (but George swapped back to his "old" spring and got the original results)
2. You have an extremely long inner barrel for the cylinder that you're using
3. You have a short barrel for the cylinder that you're using.

While the Dboys stuff is utter junk and not worth the $10 of savings vs. good parts...once it's working, it should continue to work.

A stiffer spring will not alter the nozzle to hopup fit (although this can vary between assemblies...especially if you're not consistant with tightening the stock screw).

It's really odd, because if he's using the stock inner barrel length and it's a ported cylinder...simply dropping in a s120 should net a 60+ fps increase. 30-40 if it's a really sloppy setup.

On a non-linear spring the tight pack of coils go at the back. On a Modify S120 spring, IIRC it looks more like a linear spring (at least the two I have left are not easily identifiable as non-linear). I strongly suggest you try a Modify S110. Depending on the rest of your setup....that should put you between 360-390.

Or....put it aside as a backup...but a G&P complete mechbox. Sure it costs $200 or so...but 2-3-4 evenings struggling with a problem mechbox that you end up with little to no confidence in, sure makes it seem worthwhile.

I am going to try my g&p box today with the s120 then the d-boys spring. this will narrow it down if its a hop-up airleak issue. Then I will try my d-boys box in my g&p to see how that works. At least I am lucky to have a bunch of m-4's so I can do some testing with various parts. Thanks everyone i will let you know tonight what happens.
George

I knew I was in for it when I wrote the whole gear timing part, but seeing as I spent so much time just narrowing down the problem, and comming to just that conclusion, I thought it was worth mentioning. It was the case on my friend's v2 gearbox (VFC HK 416), where he first got +-280 FPS on his new Systema 1J spring, and then when setting the gear timing differently (and only gear timing I might add) getting 330-340 FPS. We did this cause we both suspected that the nozzle was being pulled back before the piston slammed into the cylinder head. I also had huge problems getting my Echo1 P90 gearbox firing the BBs properly. It would not propel the first BB, but instead shoot two at a time every single time o.0 When test firing the gearbox outside the gun, it became apparent that the nozzle didn't position correctly. If any1 think it's an airseal problem, or that I changed multiple things at a time, save yourself the trouble. I was spending half a day just trying out different gear timings, and finally it would fire correctly. Now it shoots consistently 360-370 FPS, sadly way more than I want from the gun, so I needed to cut the spring a little.

The nozzle to hop-up seal was merely a side note, because it's a classic thing with the AR-15 series of guns. It will of course not fix this problem mentioned by George, but it's worth mentioning to everyone that cared to buy an Armalite. Please note that it's not for sealing between the hop-up unit and the gearbox, but the nozzle and the hop-up rubber sleeve. Buying and airseal nozzle might not give much of a performance jump, of course all depending on the quality of George's dboys nozzle.

What's wrong with having an AEG that shoots ~350fps? Seriously, it's pointless to upgrade to 400fps, and most often than not, will hinder performance out of most AEGs. Some will benefit large, most are very happy in the 350-370fps (w/0.20g BBs) range, even when using 0.28g BBs.

Good point! Besides there are restrictions too. Over here in Norway there's a maximum of 350 for full auto, and you should try to be careful when playing. You're also not allowed to use more than 300 FPs indoors, meaning that you can't enter a building without drawing your secondary. I'm more than happy around 1J, or 330ish, which I see many overseas playsites have set as their max limit (overseas meaning at your side ;)).

EDIT: Fixing all the possible airseal-leaks can quite possibly get the gun a lot higher on the FPS alone. That way you can actually get a weaker spring and make the gearbox last a lot longer. This is espcially the case with v2 gearboxes, that really need the relief it can get.

I think it's just that putting a 400fps+ spring in a mechbox and having it only shoot 350 creates damage and a drop in rps that can be avoided by fixing the air seals

Echo?

So heres where I am so far. I dissasembled another long m4 today to try this s120 spring. came out at 390 fps w/.20's so its not the spring.
Next I installed the g&p mechbox into the d-boys gun with the d-boys barrel and hop up. =390 fps.
so its not the hop up or barrel. Great seal in the hopup as i have allready checked it for leaks.

Next I installed the back to stock d-boys mechbox into the g&p AEG and it shoots 350 fps. Same readings as with the d-boys barrel and hop up.

I then installed a modify s120 in the stock d-boys mech box and got around 330fps in both G&P and d-boys guns.

So far i have narrowed it down to being some issue with the d-boys mechbox with a longer spring. Can't see how as it makes no sense at all. I think i will leave the d-boys mechbox stock spring in and just instal bushings and shim it.

As far as wanting higher fps, I use .28 ammo at our outdoor field and found that extra 50 fps gives me a small advantage in range. My G&P is fully done up and can handle 400 fps with no issues. I use it on semi auto only and run it more as a countersniper setup.

I agree that 350 fps is usually enough and I use many other guns shooting at that fps for most applications.
I am going to do a little research on d-boys and see if other players have done setups on thier mechboxs. I will post back

You know that once I set up my CA M24 to shoot around 340fps using 0.20g BBs, and when tweaking the hop up I was able to get my 0.30g BBs out to around 280-300ft rather easily. Just saying, fps helps but can actually reduce the range if too high. Currently I have it set up for around 400fps and am really happy with the way it shoots the 0.36g BBs for range and consistancy. And my MP5SD I recently downgraded to 360fps from 400fps since at 400fps it sucked using 0.28g BBs, but is much happier sitting at 360fps, same as my MP5A5 when it shot the same (which now sits at around 300-330fps, have to check it again).