Low FPS build

[luke213]

So guys I've come into an odd question and yes I can figure this out via trial and error but I figured I'd throw out a question and see if this has ever crossed anyone's mind as well as maybe save me some time etc.

So my son is very young just turned 4, but he's got an interest in airsoft. Now I'm not planning on getting him out playing anytime soon and shooting will be done with me there hands on the gun. But we've been shooting with my guns for the last year off and on and he always takes an interest when I'm hosting a game here.

So I got to thinking about building him a gun, originally it was buying a gun but I quickly went off that. I had planned to buy him a "boys" series gun like the old TM's. But those are not very durable and quite fragile. So I started thinking about building something sized more to him like an M733 or there about but lightweight. Since normally I could just say "here use my stubby M4" but all of my builds are heavy full metal setups and they would be too heavy. So I started thinking about taking a bunch of parts I've got around and building a light weight low FPS build. IE my goal FPS is somewhere between 150-200fps way under what would be considered a normal build. The reason is safety but also making it hurt less at this point. Now using standard parts I can upgrade the spring over time and get it to a level he can actually use it in a game once he's older. And doing it this way I can just change things as needed and it's not a waste as a cheap boys type of gun would be.

So I'm planning on building out a small M4 platform with plastic body likely, more less the lightest body parts I've got around likely front wired with a normal set of handguards for a battery. Then likely take a stock spring and cut it down, do full compression and shimming work like normal. Then likely a stock bucking and a simple barrel setup.

But then that's the question FPS, since my goal is so low has anyone figured out a means to reliably get that low of FPS. I mean I'm shooting for approximately AEP velocity which I know can't be a common thing since I've never thought to do it till now;) I could drop the FPS via compression, but I don't honestly trust that things wouldn't change or swell and all of a sudden it's shooting much hotter than anticipated. So I think doing it via the spring would give a more stable end result.

So I'm curious maybe someone has built out a super low FPS build for very close CQB or something of the like, if so I'd love to hear any tips you have etc. Otherwise I'll just plan on tossing it together based on my plan and post the results once I get it all done. This isn't a quick project since of course my son doesn't "need" this gun anytime soon. We're not to that stage, so it's more of a background project, might even end up being a Christmas present this year depending on time scale when I get around to building it.

Take care!

Luke

[T6e9a]

Thoughts for lightweight immediately went to an Aluminum gearbox shell. Match that with a plastic receiver, and the result is a LOT lighter than ang standard AEG, and the gearbox will be set for life, will never break.
But i sorta doubt you would drop ~$120 on a gearbox shell for such a build, but if lightweight you are going for, its a HUGE step.

For getting consistent FPS, no going to lie, i was thinking of a DSG. With such, just dont use m150+ rated springs. A stock spring or even maybe like an m90 would probably be right where you would want it. With it being so low stress, it will be reliable, dont even need more than a stock motor, so long as you just use say a 8.4 maybe 7.4 battery. And then as you want to increase the joule output/fps, you can just shim in a regular sector gear. Having a half cycle, it will restrict the volume and potential for "unsafe" FPS.

I have a few extra DSG gears and not much on my work bench at the moment, so ill throw one.together with stock parts and see what the output looks like, and if the hop up will work/engage as it should. I'll post back with results.

But those are my thoughts.

[luke213]

That is a great suggestion on the dsg. Your right I'm not likely to go aluminum on the shell. I have no joke like 12+ version 2 gearbox shells sitting in a bag. I bought out a bunch of parts from local guys so this will be a somewhat cheap build. Weight is an issue but not a massive one. I think a plastic body and simple front end and stock will likely be enough. Most of my guns are just heavy builds like my old CA guns everything is heavy and allot of pot metal etc. So I'm thinking non railed front end m733 length outer barrel and I'm still back and forth on whether it will be wired front or rear. Front handguard will give plenty of room for a decent lipo but I hate working on front wired guns.

The DSG though I hadn't even considered. And that's a good idea though it would drive the cost up etc. However that made me come up with another idea which is just short stroking the piston or gear to shorten the cycle. That should allow me to toss in a stock spring then cut teeth until I get close to my fps goal.

Originally I considered shortening the barrel or somehow inducing a compression leak somewhere but short stroking should be super consistent and best of all cheap. I also have a bag of around 40 stock gear sets;) So cutting down a few with some trial and error would be a none issue.

I would still be curious what you find and with what tooth count on the dsg. Since I could use around the same number of teeth and give me a better idea of a starting point.

Thanks allot for the idea though since DSG isn't something I've messed with and didn't exist 10 years ago it's unlikely I'd have thought of that or short stroking without fiddling around a bunch;)

Take care

Luke

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[T6e9a]

DSGs come in 8 and 9 tooth configurations. So you could just short stroke a regular sector gear to that, but with short stroking anything, for reliability, I recommend at least a metal rack piston. And you only have ahort stroke the sector, that way you can use the piston universally no matter what gear/number of teeth.

But yeah, ill get something basic set up and test it some, give you some guidelines/ ideas of what parts might work, teeth count, etc.

[kjones734]

A short stroked piston will work. You could also take a small drill to the piston head to create a air leak, you will have to start out small and go bigger till you find the correct size air leak that gives the desired fps.

Just a idea for safety, maybe you should make his face protection rather difficult to get off, I know little kids dont understand the necessity for face protection and may take it off and hurt him self before you have a chance to stop him.

[luke213]

Good deal I actually knew the 8-9 tooth I just meant to make sure you say which you used for the fps results in your test;)

Likely I'll throw an shs blue in this build unless I come across something in my parts to use instead.

I had planned to just do the sector. I asked some other people about short stroking in the past since I've not had a reason to do it. And several seemed to think you had to do the piston as well as sector which made zero sense to me. I intended to test doing just a sector gear and see if the results followed my theory. So I'm glad to hear you confirming that. I couldn't figure out a good reason to do both other than more work and ruining a piston that could be used elsewhere if left alone.

Take care

Luke

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[luke213]

On the face protection that's really the main restriction to him playing. Or one of the main ones until I can trust him to have eyepro on and keep it on he's not going to be in any sort of game even with his cousins.

I might do a helmet/eye pro combo we'll see but that's on my list for sure. Right now he's used my shooting glasses but that's just been plinking etc.

Safety though is going to be a priority on eyes and important bits. On other stuff I'm sort of thinking he'll have to learn to tough it out to a degree We were shooting his dart guns the other morning in the house and I started with talk about eye protection and making sure he kept them on. He did pretty well after getting shot in the body with a dart and coming to the conclusion he didn't want to get shot in the eye with one. So he's a pretty sharp kid on that front. However that's also the reason for taking things this direction. If I built this tomorrow he would get to use it when he's ready, rather than when it's done. But being a dad I'm also excited to see him taking an interest in the hobby even at such a young age.

Luke

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[T6e9a]

The thing with just short stroking the piston, is that unless you match it, tooth for tooth the sector, you will likely lock up the gearbox.

And really the only reason to dremmel off excess piston teeth is for builds trying to get as fast as possible, as quick of a piston return, but isnt really applicable.

And im going to start with a 8 tooth DSG and a 3/4 cylinder to start with a medium stock spring, which might put out 330-350 in a standard build and probably a ~300mm barrel. Ill try stock and TBB. See if there is any accuracy diffrrence between the barrels with such low output.

[luke213]

Sweet would love to hear the results. I suspect that this build should honestly be capable of hitting around 50 yards. I theorize that we're around the same velocity of an AEP and I've been able to test those hitting around that range plus or minus a couple yards. Which should make this build functional but also not prone to hurting the person being shot etc.

Likely depending on how this works his cousins will end up needing the same basic build before long etc. But it's an interesting project. Sort of makes me want to build something low fps just to see how it goes for close up. That's actually a feature of the AEP's that I really like. I don't feel bad shooting someone close up with them and I feel less bad if it's even a burst of fire close up. So I'd be curious to hear your results.

Luke

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[T6e9a]

Alright, so I threw the few parts together as stated before. And with a spring that probably would output 370-390, it is putting out 240 consistently with a ~265mm stock barrel.

So my next step is a weaker spring and a 1/2 ported cylinder(or less than 3/4). Once i get it between 150-200, then ill work more so on the hop up and range/accuracy testing.

[luke213]

Good deal man appreciate it. Don't take too much time on my account unless your curious as well;)



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[T6e9a]

I am rather curious if the potential as far as range/ accuracy goes. Sorta on the same idea of TMs being generally low powered compared to what most people want, but still out perform the majority. So long as I dont have much else on my bench, I have some motivation to check into it.
I imagine though, .25s in it would be like running .40+s in a TM haha.

I will see tomorrow and get back with more results.

[luke213]

That's sort of my question too. My typical builds are touching the FPS limits, so if I'm building a normal gun it's typical that I'm right on 400fps, or 550fps for a sniper rifle. Mostly because I like to get the most out of my guns range wise and while FPS isn't everything, FPS combined with the rest of the work makes for a better long range gun.

But I've also encountered guys getting pretty heavy welts and myself getting them from some of the higher FPS builds which are far more common than they were years back. So when I got the AEP I was surprised at the range and accuracy for such a low FPS gun. And of course TM guns in stock form are quite effective out to around 55-60 yards in most cases while still running pretty low FPS by modern standards.

So this project idea started as purely let's build a safer and less dangerous airsoft setup for my son, to me being curious what a low FPS build is actually capable of. I know what higher FPS stuff can generally do, and I'm very familiar with the 270-300FPS range from stock TM stuff, but I'm now wondering what is the lowest FPS I can build that will carry a BB around 50 yards;) Is it 150? More of curiosity than anything else but lower would be safer which would be nice.

I will say BB weight might start being an issue, I know on my AEP I tend to run .25g mostly since I don't keep .2g around anymore. But .25g is pressing the FPS/weight limit quite a bit they are slow at a distance. That said I get allot of close up sub 25 yard kills with that gun, more than most guys would expect. Granted often I'm running a high FPS primary and use a secondary more than allot of guys. But the low FPS doesn't necessarily mean useless either;)

Luke

[T6e9a]

And useless it isn't, but range of usable bb weight is small.

I was finally able to drop the FPS to about 205 with .20s and 185 with .25s.
The current setup:
228mm stock bore barrel
Random stock bucking
1/2 port G&G blue aluminum cylinder
AoE corrected behind piston head on full poly piston(just testing and low stress, so doesnt matter to me right now)
Stock ICS motor
Weakest, complete spring(no coils cut) in my collection
G&G stock plastic hop up

I would probably recommend flat hop for this sort of setup.

It worked beautifully with .20s, but jammed with .25s with the hop needed to have a level trajectory. If i could, i would probably go with as soft of a bucking as i can, just to prevent possible jamming and to grip the bbs best it can. Additonally, a flat hop might work better.
Due to my limited testing range, i would say it can reach past 100' with .20s, but even the slightest wind will carry them way off course.

Its performance definitely suprised me though. The idea should work great for the application.

[Snarf]

For a four year old, I would just say buy one of those "mini" AEGs with a plastic gearbox...but wow did this thread take off! It kind of reminds me of the <1 Joule challenge I saw somewhere (airsofsociety I think). I wonder how much performance you'll be able to squeeze out of that low amount of power. Best of luck on the build(s).