Need opinions/advice on a bb gun design

[gpopovic]

Hello!
I’m new here, I’ve been reading the forum for a while now, and would like some opinions/advice on my design. It’s sorta reverse engineered BB76, I like it, but can’t get it in my part of the world, so after looking at some pics of it disassembled, I came up with my own version. I’m familiar with repairing cheap plastic bb guns, cause my son regularly breaks them 
I would like some advice on whether or not this would work, have I overlooked something etc, any help would be very appreciated!
I have some more designs done, but this one has the best chance of actually being made real.

Thanks in advance!

Goran
bb76 based idea by Goran P, on Flickr[/img]

[cammyd32]

Would it work? yes, it's a tried and tested mechanism, similar to most spring air guns.
If you're really interested in the mechanics of it, it's worth a visit to this website,(the more useful links are about half way down the page)

The theory is sound, It is however, as I have found out the hard way, quite difficult to pull off in reality, especially without access to machining equipment. If you do, great, it's a simple and effective design, otherwise, it's certainly possible, but I found making a lightweight, low friction but good sealing piston is quite a challenge out of botched parts.
Also what is often overlooked is a good sealing detent for the barrel, one of these can boost power for a springer quite considerably.

One point I also think is worth mentioning is be careful with build quality, and don't overdo it with the spring, a badly made springer can be quite dangerous (strong compressed spring very near face) especially if this is going to be your kid using it.

There are quite a few examples of people who have pulled it off successfully, both machined and non-machined, I'm sure I can find them somewhere if you are interested.

But otherwise, yes, if you have the build skills then it's a good design, and as you have drawn it will work.

[gpopovic]

Thanks a lot! It's for me actually, the measurements on the pic are completely off, I scaled down the drawing to export it as a jpeg. It's supposed to be 1350mm long.

I didn't intend to use any plastic bb gun parts, repairing then just gave me the idea. In my photostream you can find a before/after pic of a cheap bb rifle that we have bought broken, so I made a new wooden stock for it, got rid of all the not needed external stuff, changed the barrel and filled the hollow halves of the action with hot glue for some more rigidity. There's also a wooden Colt Walker with plastic springs What is left is to do is to make all new trigger group out of alu and swap the original plastic bits. Spring was untouched, but I think the rifle looks a bit better than it's original state

bb upgrade by Goran P, on Flickr

I make guitars, so making everything but the piston and it's syringe like counterpart is no problem. I have an option of getting them machined out of aluminium by the nearby shop, and the piston head could perhaps be from large medical syringe, easy to get and cheap to replace?

The other option is to epoxy the syringe body into a close fitting tube, and make a new "nose" and the smaller tube to put the piston head onto. I should be able to pull that off in my shop.

Any thoughts?

Thanks again!

[gpopovic]

I have a weird little gun almost finished, alu 10x2mm barrel, steel pipe reservoir, schrader valves both for filling and shooting. Stock is a piece of cherry, oiled, then waxed. I did some checkering by hand, first try. Action is made out of acrylic, bolt seals the barrel. It's basically a larger version of simple launchers I've seen on the youtube. I need to glue the schraders in the tube using epoxy and I think it's done.
airsoft pcp rifle by Goran P, on Flickr[/img]

[cammyd32]

Picture hasn't shown, sounds good though, have you got another link?

With regards to making the piston, a modified whole medical syringe would work, and would be cheap to replace, but I always found them difficult to work with as they aren't exactly designed with structural rigidity in mind. (eg quite fragile + hard to attach reliably to things)

Machining the piston and cylinder would probably yield the best results, both in look and in function, you can buy o-rings cheaply on ebay, and designing a groove for them isn't hard with the right know how, also means you can cheaply and quickly replace the rings if you need to change them, most high end bb springers have machined pistons with o-rings in this format.

My advice would be to completely try and avoid using 'cast' epoxy for the piston, if you do the friction with the walls will be too great, also solid epoxy can add up on the weight quite a bit.

By the way, great work on some of the things you have made, I used to repair cheap bb guns from second hand shops and sell them on, so I see the amount of work that you've put into some of those.
Also that airsoft pcp rifle looks good, is that what you were talking about in your previous post? If so it looks really good.

[gpopovic]

Thanks for the advice, I'll try to get the cylinder and piston machined, probably aluminium. O-rings are easy to buy here, and cheap, so no problem there. My idea for the syringe was to epoxy the syringe cylinder into a close fitting pipe, still might play with that a bit. Then i could substitute the syringe piston for another alu -pipe, just using the rubber head.

Yes, the pic was supposed to be of the PCP rifle, don't know what went wrong - thanks for the kind words. I've been making things for a long time, but most of airsoft related stuff started with my son breaking his cheap bb AK - I had nothing to lose, so I took it apart, took some photos to be able to put it back together, and it still works to this day. Then I remembered my old Zastava air rifle I once had, got the bug and started putting back together all the broken bb guns I could find...and I'm supposed to be building guitars

[gpopovic]

Did some more drawing, and came up with this - I had to change the shape of the lever a lot to get it right, and also not to change the overall shape of the action. I did stretch the action a bit to get a lower pivot point for the lever, but I don't think it is that readily visible?
https://flic.kr/p/ssjJS2

I plan to make the action out of plastic acrylic sheets, produced near by, which are easily welded together with CA. They come in many thicknesses, so I can get really nice, machined-like results. The bond is really strong, I've made 3 actions for cap guns this way.
Her's the first one, based on the Remington RB:
uros puskica by Goran P, on Flickr

I have a winchester-shaped stock blank out of cherry, cut oversize which could become a part of this project.

So the mission is to make a technical drawing of the piston and the cylinder, and see what would the cost of the machining be? If OK, I would order 2, and probably make both

I made an attempt at shaping a 8mm round stock steel into a lever, which is promising - we have an anvil in the yard for some reason so I pounded it in the shape roughly, did the sharp bends in the vice, and flattened it where needed, then thicknessed it more accurately with a file. Looks nice enough, it just needs one weld to close the loop, and some hardening. Pic to follow.

[gpopovic]

Another revision - realised that the trigger is upside down



Broke the piston/cylinder parts down, going shopping soon, so I need a shopping list. I will solder the parts together and try at least, to do the lathe work on the drill press. Still choosing between the round ring and the square one, probably square one.

Anyway, here's the sorta exploded view, preview and the actual mechanics of it.

I intend to start making it soon, so comments are more than welcome, stop me in time if you see any mistakes

Thanks!

[Doodmens]

That looks very professional! I really like the stock you carved, I'm also going to try carve one soon but I think it won't nearly come out as good as yours... do you just use a chisel or also some other fancy (power)tools? On the gun, I'm way too noobish to say anything about the correctness of what you drew, sorry for that. I haven't dared to do anything DIY piston related yet. Looking forward to see more updates!

[gpopovic]

Thanks a lot!
When you start the carve, just ask me if you need any details on what I did here. I might have a few pics of the process...
Regarding the tools, nothing fancy really, I've cut the outline with a jigsaw, and the inleting was routed first, fine tuned with chisels.
Outside was carved with half round and flat wood rasps, then rasps for metal, they leave a nice finish, scrapers and finally, sandpaper of various grits.

Checkering is scalpel first for the lines, triangular curved small file second, kinda slow and unprecise, but it worked. Oiled and waxed. The wood is cherry, btw.

[Brian the brain]

That, to me, is the best stock I've seen so far.
The checkering really puts it in another level!

Врло лепо!!

[gpopovic]

Hvala puno

Thanks a lot Brian! I've been looking at your rifles for a few weeks now, hoping to make something simillar at some point. What I don't understand is how do you refill a coaxial valve for multiple shots? Is there another valve somewhere that I can't see that when opened, refils the coax? Thanks!

[gpopovic]

Found a few pics of the making of the stock...it was first a springer, but the finished rifle was to hard to cock without a lever, so I reused the still-in-the-rough stock for a PCP with really small modifications. The tube and the piston are still around, waiting for a better idea ...

kundak pravljenje by Goran P, on Flickr

[Doodmens]

Really cool! Thanks for posting. I hope to come close to your skill level in woodworking one day
I guess it takes just a lot of practice and patience

[gpopovic]

Thanks a lot! It's not hard really, nor that time consuming. Start with a nice piece of wood, sand the outline nicely when you cut the shape out, use the squareness of the blank to route the inleting using the routers rail guide, and shape all the round parts of the stock one facette at a time with a rough rasps.

Scraper is in the pic, spare scalpel blade where you can use a screwdriver to turn the burr in the vice. It takes care of the rough rasp marks quickly, and then its metal files, sandpaper...etc.