3/4" Copper Full/Semi-auto

[skyjive]

This is my second attempt at an automatic design, the first was cylinder-actuated (its posted here somewhere) and was basically a failure due to a glacial ROF. This design uses a blow-forward bolt instead. Lets start things off with a firing video, five shots at about 70 psi into an old trashcan filled with old sheet to absorb impacts. Once the covering paper is destroyed its kinda hard to see the follow-up shots. This video is with the semi-auto/blowgun attachment in place:

[youtube][/youtube]

The gun has 60" of 3/4" type L chamber and 51" of 3/4" type M barrel. The firing valve is a McMaster 3/" QEV. The gun can be filled through either a Quick-Disconnect setup or a shrader valve for use with CO2 canisters or bike pumps (the former for rapid fire, the latter so I can test it without using up gas). The QEV can be piloted either by a blowgun or a 70 psi pop-off valve, allowing semi or full auto firing characteristics. The rate of fire at full auto is about 1.5 rps, slower with semi because the blowgun drops the pressure lower after firing, requiring longer refill time. The magazine is made of wood and can hold about 15 rounds. The ammo in the video is simply dowel sections wrapped in duct tape, but also usable in this gun are steel-tipped darts (not suitable for firing in my basement into a target 3 feet away!). Why not go outside, you ask?


Some pics:


(almost) the entire gun


Looking down the barrel. The magazine is offset to one side to allow a clear(ish) line of sight and for better support.


The blow forward bolt housing and feed tray (shown without magazine obviously)


Bolt open


Bolt closed


From top: a ruler for scale, a 3/4" steel-tip dart, a shell from the original shell-ejecting design (couldn't make it happen, unfortunately), the blow-forward bolt housing, and the bolt itself.

And finally a video of a couple dry fires to show the bolt operating (yes it can shoot faster):

[youtube][/youtube]

[starman]

It won't win any beauty contests but I like your ingenuity on the thing.

Where are you located, getting that much snow?

[ALIHISGREAT]

the chamber shape is unique!

but kudos for the 'semi-auto' :thumbleft:

[SP00K]

Dang!!













You've got a lot of snow.

[raptorforce]

how does it work what makes the barrel move forward. i would have made mine but home depot was like "o no we have springs there over there but they werent there so i spent 15 minutes looking for something that wasnt there" very cool design maybe ill have mine working soon

[Sticky_Tape]

The air pressure pushes the BOLT forward.

[raptorforce]

The air pressure pushes the BOLT forward.

and this would be done by?

[Floyd]

The air pressure pushes the BOLT forward.

and this would be done by?

http://www.spudfiles.com/forums/6mm-sem ... 10075.html

That link shows a variation of what is being done here.

@Skyjive
Looks great! How long was build/design time? A little polishing would make it better. Maybe get a smaller magazine. I'm liking the shape of the chamber. How is it to hold?

[skyjive]

I live in New England, and we occasionally have massive winter blizzards which provide a convenient excuse to not do anything but build more weaponry. The chamber is shaped that way because my original design called for a vertical magazine under the barrel so I needed to get the chamber out of the way, and then I ran out of money so I couldn't redo it. I've been working on it for a couple weeks and am still fine-tuning it. I might reduce chamber volume for higher ROF and sometimes is mysteriously refuses to pilot, but it works pretty well.

[psycix]

Nicely done on the blow forward bolt!
Cruelly done on the chamber shape!

If I understand it well, you just keep the air feed on while pilotting?
Note that the higher the air feed, the worse the pilotting thus the slower the opening time.
Though I think that the opening of bolt takes up enough time to compensate for the slow opening time of the valve.