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Wacky Breechloading Launcher

Posted: Wed Sep 14, 2016 6:25 pm
by Dig_Gil
Developing from my last original post about coaxial launcher concerns, I've came up with an interesting concept I want to share. I'm not sure I will ever build anything practical out of it, but I'm interested to know your impressions.
Maybe It's an idea that makes possible my pipe-dream of a full-auto marble launching bullpup airgun... Maybe it's too complex to construct and get working...

Here's a sketch of the shooting sequence:
Shooting Sequence Sketch
Shooting Sequence Sketch
It's an oversimplification to explain the concept.
Here's the details:
It's a Coax design, obviously. It uses the Chamber pressure to open into the Barrel.
If you look closely, the Barrel is flared. It has a lot of upsides: better flow, less jamming when loading a ball and easier to seal properly without sticking into the Main Piston's orifice.
Green little streaks are the rubber Seals and O-Rings.
There's a tall tube filled with balls/marbles which works as a magazine.
Red part is the Main Piston which is pushed by Chamber pressure.
The Barrel is kept sealed by the Main Piston being locked in place (see blue Latches).
Blue Latches are the tiny pieces in the bottom of each drawing with an axle each. One of them is connected to a trigger and the other is unlocked by the Bolt when it reaches the end of its travel forward.
Bolt is the orange part that drives within the Main Piston. Although I call it a "Bolt", it's more akin to a bolt carrier/striker/actual bolt hybrid in a firearm. The only thing it doesn't do is interacting with a locking surface but the trigger's. It isn't supposed to be affected by the Chamber's pressure, most of the time at least. Because of this fact a manual handle can be used to manually cycle the feeding in case the last round jams or didn't load properly. Kinda like a firearms bolt handle!
Lastly, the blue bars behind the Main Piston and Bolt are Springs. They simply push forward. Their combined force should be larger than the force exerted by the chamber pressure. The Bolt's Spring should be too strong as to stop a person from manually cycling it if needed.

I imagine the manual feeding be accomplished by rotating the Bolt using its handle. The Bolt will twist the Main Piston in such a way it exposes the two Balls contained within to an cut-out on the side of the Receiver. If there are no Balls there, you could insert them now.

The magazine would be a spring-loaded horizontal tube (unlike what's drawn) with marbles which at Stage 1 drop into an antechamber in the Main Piston and the channel space within. They are kept from rolling away by spring wire or a loose o-ring. Maybe I could design it without the antechamber, but I like it being there.

At Stage 2, the trigger is pulled and the Bolt is let off to push through the first marble in its way. The marble is pushed into the Barrel. The Bolt hits the Main Piston's Latch unlocking it.
If the Marble is too large or unevenly shaped it won't fit in the barrel and jam the Bolt. The jammed Bolt is unable to trip the Main Piston so it won't shoot. By this time, the user can pull the handle to recock the Bolt and proceed to manual feeding (or, in this case reject the marble).

Chamber pressure pushes the Main Piston away along with the Bolt because it is in the way. Air rushes into the Barrel, pushing the marble along. Now here's a problem I recognized in this concept: Originally I thought the Main Piston would mechanically push the Bolt all the way back, but I can't figure how that's geometrically possible. I wanted to know if it was possible for the Chamber pressure to push the Bolt the last half way of travel before running out of enough pressure. Assuming that to be the case, the Bolt would eventually be caught by its Latch. The Chamber pressure would drop enough for the Main Piston Spring to return the Main Piston, sealing the barrel again. We're now back to Stage 1.

To guarantee that pressure in the Chamber drops low enough for proper cycling, a Choke is used to delay the filling of the Chamber. Maybe, in a needlessly complicated variation of this design, one could have the Main Piston to lock the Regulator closed, but I digress.
To enable automatic shooting, the Regulator's piston could have a linkage that trips the Bolt's Latch, so that when desired pressure is reached in the Chamber, the Regulator shuts down and pulls the trigger at the same time.

If I were to build this, maybe I'd lock the Main Piston by using a tilting block, like the SVT-40 or FNFAL rifles. The Bolt would be latched by a trigger group similar to a crossbow's and actuated by bicycle cable. The Magazine would be a fixed, top-feeding, tube. Maybe a en-block clip could be designed for it. It would be cool if it had an hopper like the Krag–Jørgensen rifle, but I don't really understand how it works.

After rough optimistic measurements, I think this breech system would require about 120 millimeters of length which is great. Maybe the length could be reduced further by using a spring-loaded arm like in the Webley semi-auto pistols. May the Main Piston could be attached to a sleeve inside the Chamber and be pushed by a spring embracing the Barrel. Similar to what some pistols do. Maybe the Bolt could be a hollow tube containing its own spring. Etc. Etc....

For now... That's all folks!

Re: Wacky Breechloading Launcher

Posted: Thu Sep 15, 2016 11:41 am
by mrfoo
I've been considering something very similar.

Re: Wacky Breechloading Launcher

Posted: Fri Sep 16, 2016 4:50 am
by Doodmens
Nice, I think this is a very elegant design. Curious to see how it will perform. Hooking up the trigger cocking to the regulator piston something I hadn't thought of before...

Re: Wacky Breechloading Launcher

Posted: Fri Sep 16, 2016 9:50 am
by Dig_Gil
Doodmens wrote:Nice, I think this is a very elegant design. Curious to see how it will perform. Hooking up the trigger cocking to the regulator piston something I hadn't thought of before...
I'm glad you like it. I think it was Leonardo daVinci who said that true sophistication is simplicity. I waste a lot of time with complex designs of inventions which could very well work if babysitted enough, but I keep throwing them away in search of an holistic, "do-no-more-than-required" kind of solution.

I still wonder, myself, if the recoiling of the Bolt would work in practice, given that the Main Piston can't push it all the way. Maybe some of the Chamber pressure could push it too, but it would be less than ideal if there was a substantial amount of pressure venting through the magazine port and rattling all the marbles or maybe injuring the user. Maybe, with proper tuning, the acceleration of the Main Piston could be transmitted to the Bolt so that it completes its travel by inertia/recoil alone.

Re: Wacky Breechloading Launcher

Posted: Fri Sep 16, 2016 3:39 pm
by Doodmens
I must agree with DaVinci then :)

You should throw some math at it to see under what circumstances it would work. I wonder though, what do you exactly mean by choke? Something to time when the air enters the chamber, but how? (if not manually)

Re: Wacky Breechloading Launcher

Posted: Fri Sep 16, 2016 5:52 pm
by Dig_Gil
A choke is simply a narrow passage were air purposefully leaks in very slowly. There are industrial valves which do this, but it can be simply accomplished by forcing the air through tight passage, or a pinched tube.

Re: Wacky Breechloading Launcher

Posted: Sun Oct 30, 2016 7:35 am
by Dig_Gil
So, I've been away, thinking about this concept further from time to time. Most difficult was to optimize it geometrically and come up with ways to regulate and trigger it in the correct sequence. I wonder what those guys posting about cartridged projectiles with in-built pressure chambers think of this :twisted: .
Advanced Co-Axial Airgun Concept
Advanced Co-Axial Airgun Concept
Because it has many moving parts it's a difficult build, specially at the Feeding Stage when the gasket of the bolt rubs against the Bolt Carrier's interior, which might result in much friction and stickiness.
To ease things up, this new design is self-regulating (somewhat). The Bolt Carrier features double o-rings to isolated the Reservoir from atmospheric pressure, but also a single gasket which seals against a narrower section of the Chamber whenever the Bolt Carrier is pushed fully rearwards (due pressure in the Chamber). I imagine that instead of using different sizes of tube to make the Chamber, there would be cuts in the Chamber walls where required for air to loop past the gasket.

This new launcher is quite complex and requires two latching/locking systems. I left these underdeveloped and the drawing only shows the one which is active at each stage because they overlap and it would be confusing to look at.

The first locking system holds the Bolt open while the Chamber is emptying from air. As pressure falls below the Carrier Spring force, the Carrier will travel forward. At the end of travel it should trip the Bolt hold-open. The Bolt drives a bullet into the barrel and the second latch locks it there so that it doesn't move as the Chamber fills up again. Because Chamber pressure pushes the Carrier around, it will travel fully rearwards where it trips the second latch which is also held by the manual Trigger. Keeping the Trigger pressed allows full-auto function. To ensure it will only shoot when Chamber Pressure is high enough, there should be a very short regulator-strong spring (not represented) at the tip of the guide rod. The guide rod is then connected to a sear to trip the locking device.

From the represented springs, the Bolt spring is the strongest: it acts both as buffer during recoil and is required to slow down the travel of the Bolt Carrier to manageable levels. Mainly it works to return the bolt forwards, so it might have to be stronger than the Action Spring, although, geometrically speaking, maybe not.

The Action Spring launches the bolt backwards very quickly to discharge the Chamber into the Barrel. I figured out this action method, because I calculated the force acted upon the Bolt Carrier to be insanely large ( given a 16mm bullet) for the locking system to handle. So, the Bolt Carrier is alway seating against a solid surface and the Bolt is pushed open, not by pressure (directly at least) but by spring force which can be adjusted. In theory the stronger the spring, the better, as long as the locking surfaces can handle it.

The Bolt Carrier spring only requires to beat friction and as such is the weakest. It should push the Bolt Carrier forwards when it is safe to expose the chamber to bullet pathways.

I'm trying to keep this post short. If you want details, you know what to do...

Re: Wacky Breechloading Launcher

Posted: Sun Oct 30, 2016 8:13 pm
by mobile chernobyl
Interesting concept - Double spool using one to control chamber flow - It would probably work as you would expect, provided you calculate your surface areas to achieve the balanced/unbalanced effect you desire. It is pretty complicated for sure though - take a look at for some ideas on similar spool and spool within a spool ideas used in paintball!

Your idea reminds me of this marker - not the same for many reasons, but achieves a similar action with both nested spools: ... _15fps.gif

Re: Wacky Breechloading Launcher

Posted: Mon Oct 31, 2016 10:17 am
by sharpshooter
Holy cow!! SO many animations! You guys are not helping me avoid buying a lathe.

Re: Wacky Breechloading Launcher

Posted: Mon Oct 31, 2016 2:52 pm
by mrfoo
Give in to your interior machinist...

Re: Wacky Breechloading Launcher

Posted: Tue Aug 01, 2017 5:24 am
by Dig_Gil
So, I had a someone PM me about this launcher, so I went to iterate over it again. This new version is more compact, can work with simpler lockwork (although in the drawing is simplified) and at last it has some means of manual extraction.

The drawing doesn't feature the self-regulation feature because I wanted to make it simpler and clearer, but it's the same as the last design. If you were to build this, you might want to have an external, factory-made regulator for more reliability anyway.

Some choke into the pressurized chamber must be in place to tune the timing of the carrier or the feeding will jam.

If you want to access the bullet chamber, for extraction or single-shot reloading, you can have a handle on the carrier, push and rotate it like a bolt action rifle, so that it is as if in the "Feeding State", and use the cut out ahead of the magazine to look inside. The carrier could have sort of a in-built lever to work as extractor, which usually is spring-loaded to pull the bullet into alignment with the barrel, but can be manually operated to aid at pushing the bullet through the cut-out. Otherwise... you know... use gravity.

This is probably the last iteration of this layout that I'll make. I've started moving on to a different feeding mechanism which, although not as clever as this one, it's probably better overall as it can use exactly the same lockwork on proved firearms.