New build - 10mm bullpup selective fire semi / auto

[evilvet]

Hi all

After a fair bit of experimenting I have a working prototype

• Bullpup form factor
  10mm ammo
  Electronic semi / auto selective fire
  Inbuilt safety

"Moah powah" was not a consideration, this design has a lot of faults and was built to learn from them. Issues I have right now include dead space between the valve and breech, lack of a propper detent to prevent rollout, plus a few other things.

The red-green LED is activated by the pressure switch in the butt plate; pull her in tight, green means single shot, loosen the grip a little and red means auto.

Any comments and advice appreciated.

Build photos are below:

[LovableAirGuns]

WOW nice job. How far can it shoot and have you got any damage pics or videos?

[JDP12]

wow! Very impressive for a beginner... Could you give us some more detail on the way it operates- the electronic parts and the valve?

[evilvet]

WOW nice job. How far can it shoot and have you got any damage pics or videos?

I need to get the tripod sorted out so I can do some video but as far as range, 15-20 metres, at that range impact into timber is enough to shatter the plastic BB's I am using.

[evilvet]

wow! Very impressive for a beginner...

"Electronic" is an overstatement; the butt plate switch actuates the solenoid plunger housed on the breech to create a blockage and prevent more than one round at a time entering the breech. The bi-color LED's were salvaged from a photocopier and were added just for fun.

The valve is controlled by the separate trigger switch, just a standard solenoid valve fed from the shop compressor at 120psi.

[wyz2285]

How do you select between full auto/semi auto?
I´m building a simular gun but shots bbs

[jackssmirkingrevenge]

Brilliant but you can't post something like this without videos, let's see it in action!

[evilvet]

How do you select between full auto/semi auto?
I´m building a simular gun but shots bbs

As I said, the pressure switch in the butt controls a solenoid plunger. If the plunger is in, no rounds can feed from the hopper so it is single shot. When the plunger retracts the hopper can feed freely.
See the photos marked semi and auto.

Two comments on your BB scale project:

I tried for weeks to get a plunger that was fine enough to split between BB's without causing a jam, in the end that's why I went with 10mm ammo.

The other thing I tried was to mount the plunger co-axial with the barrel to reduce the form factor; the right angle plunger looks dumb and is bulky. The problem is that given the straight through flow from valve to muzzle there is no room on the breech to fit the plunger in line. I am making a new breech design that has the air feed from the bottom and the plunger at the rear. Gravity still takes care of the feeding, the plunger just prevents more rounds dropping from the hopper.

That will means a complete rebuild of the receiver / stock etc so a few more nights of CNC before that shows up.

[evilvet]

Video time

http://www.youtube.com/watch?v=svM18ikFwYM

Cheers

[jackssmirkingrevenge]

hehe I don't know whether to be offended or honoured

Good stuff, though the impacts are hard to see - it would be better to have the camera set up closer to the target and have the actual sound of the shots audible in the video. And maybe a slightly harder target, like aluminium sheet from an opened up pint can

[evilvet]

hehe I don't know whether to be offended or honoured

Nicely put

I couldn't resist the target idea once it came to me, no offence intended.
I am going to start on the new build tomorrow night, a much more compact co-axial design and probably using 0.177 rounds if I can resolve the jamming issues I had in prototyping.

[jackssmirkingrevenge]

I couldn't resist the target idea once it came to me, no offence intended.

None taken

I am going to start on the new build tomorrow night, a much more compact co-axial design and probably using 0.177 rounds if I can resolve the jamming issues I had in prototyping.

As suggested earier you should make a few more videos with this build first, successful select fire with an electro-pneumatic is something few members of this forum have achieved.

As to the jamming issue, have you thought of perhaps a rotary interruptor, a coaxial design like the one below or tangential to the barrel?

[evilvet]

I take it you mean a ported cylinder, motor driven at say 100-200 rpm with each cycle allowing one round to drop into the breech ? As the port rotates to <>180 degrees it allows the air feed in. When it returns to <>0 another round drops in and the cycle continues.

Assuming 0.177 rounds and a 4.5mm aperture on a 4.5mm diameter cylinder to minimize blow-by and 100rpm that equates to a 14mm circumference moving at 1.67mm per second so a portal time of about 2.5 seconds.Would a dwell time like that be long enough to allow sufficient air flow to the projectile ? I certainly think so.

Cute and easy to do, I hadn't thought of that but it would work nicely with the mini gun / GAU-2/A mock up I have been thinking about.

The more I think about it the more I like it. A stepper driven from a PIC or just a basic DC motor with PWM driver would work nicely.

Thanks Jack

[jackssmirkingrevenge]

I take it you mean a ported cylinder, motor driven at say 100-200 rpm with each cycle allowing one round to drop into the breech ? As the port rotates to <>180 degrees it allows the air feed in. When it returns to <>0 another round drops in and the cycle continues.

Assuming 0.177 rounds and a 4.5mm aperture on a 4.5mm diameter cylinder to minimize blow-by and 100rpm that equates to a 14mm circumference moving at 1.67mm per second so a portal time of about 2.5 seconds.Would a dwell time like that be long enough to allow sufficient air flow to the projectile ? I certainly think so.

Cute and easy to do, I hadn't thought of that but it would work nicely with the mini gun / GAU-2/A mock up I have been thinking about.

The more I think about it the more I like it. A stepper driven from a PIC or just a basic DC motor with PWM driver would work nicely.

I had made a basic prototype here and performance was pretty crappy, then again it wasn't very well built and I was spinning it fair fast. Rather than constant rotation I was thinking you could have a stepper motor and then have a valve on a separate circuit.

Another option would be to have it tangential to the barrel as in this design:

[mark.f]

Nice video! Nice to find another CCR fan. As to putting the solenoid inline (not exactly coaxial) with the barrel, have you considered an electronically powered blow forward bolt? I can see several advantages (the flow restrictions required to get a normal one to work can be removed, no return spring, more compact sizes possible) so it's not exactly pointless.

Good job nonetheless.