BACH – Bolt Action Cartridge Hybrid

[daccel]

This started as a pneumatic cartridge, but I caught the hybrid bug and it evolved to this.

Most of the design is based off ideas already on spudfiles. My goal was to merge aesthetics and utility, and I think it came together nicely.

Specs:

Fuel: Propane/air
Nx: TBD
Ignition: #0 steel wool fuse, 9v battery
Burst disk: TBD
Receiver: 1” aluminum tubing
Bolt: ¾” type L copper, two steel lugs inc. handle
Chamber: 1.1” cu – ¾” type L copper, cross drilled at epoxied fittings
Barrel: .54 caliber – ½” x 20” type L copper
Sound suppression: Integral – 3.5” cu with ¼” x 8 porting @ 1.5” from tip
Ammo: 3/8 ball bearing glued in ¼” steel nipple (.535” dia.)

Haven’t tested it yet, still have to build the fuel meter, then I should be able to get some video up.

Excuse the ghetto tape, I dropped it and cracked the stock and didn’t want to put more energy into that until I test it out.

[ckman]

VEry VEry nice I love it looks nice and sleek

[skyjive]

Looks great, the bolt action looks very cleanly done

[STHORNE]

very nice, but i would suggest a more reliable form of ignition. Perhaps a bbq spark lighter or even a little piezo from a long-nozed lighter?

Again, nice work.

[starman]

Looks really promising. Have you worked out how you're going to hold and seal your burst disk? Also for a chamber this small your fueling will be a challenge...but not impossible.

Please keep us posted on your progess with this cannon!..

[jackssmirkingrevenge]

Certainly looks like it has potential, does the bolt action extract and eject the spent cartridge too?

[daccel]

Thanks, yeah it better work after all that effort!

I chose that form of ignition because of reading about spark gaps having to get smaller and smaller with higher mixtures, and it didn't sound fun having to fiddle with that. The trigger is spring loaded with a switch, and lights the steel wool every time, so so far it appears reliable. I attach enough to the end of the schrader that there are multiple ignition points which is also a bonus. I'm not sure on battery life or delay to ignition with a mix in there, we'll have to see.

The burst disk will be held in the 3/8 (drilled out) flare fitting, see cartridge picture above. There is about 3/32 of a lip left, hopefully that will be enough to hold the disk. If necessary I can insert an o-ring. Fueling is worrying me because as you said it's such a small chamber. I have 0-30 & 200psi gauges, hopefully that gives enough accuracy.

The bolt doesn't extract the cartridge yet. There is a gap between the head of the hex bushing and the copper pipe I left for this, though. Played a bit today with trying to get a peice of metal shaped like this --^ off the end of the bolt that would grab the groove in the cartridge, but no luck. I'm sure it's doable, just ran out of patience for now, but it's still on the list.

Edit: I forgot to mention, if it wasn't apparent... the schrader/fuse holder touches a contact in the center of the bolt. There is a wire running from this through a slit in the bottom of the bolt to the trigger. The other lead connects directly to the aluminum which in turn makes contact with the outside of the cartridge to complete the circuit. The battery is housed in the butt and the wires run through a hole drilled from there to the trigger.

[jon_89]

Looks good. You could use a syringe for metering.

[clide]

That is really slick, looking forward to seeing it work.

[frankrede]

Looks good. You could use a syringe for metering.

I don't believe that would work....

[Copperboy]

Wow, this was a nice cannon on a booring saturday morning like this! Beatiful! Really hope the metering isn't a problem... can't wait for more!

[psycix]

Nice!
How many cartridges are you going to make?
And how will they hold the burst disk.

[ALIHISGREAT]

Looking good so far, i've always wanted a bolt action hybrid cartridge cannon... i'd like to see how this turns out

[daccel]

Well, another day closer but still no finale. Ran out of light at the end of the day.

Got the fueling together - hopefully I don't run out of propane . I can just use the mix calculator in HGDT right, post fuel inj and post air inj?

The burst disk was being difficult, but I finally managed to get it to seal by putting an o-ring in. It's just layers of aluminum foil.

The ignition was also a problem. The wire through the bolt was getting caught on the lug and pulling apart. I have a solution with using a spring inside the bolt to carry the current, but for now I'll just have an external switch to keep things simple until I can get it to fire consistently.

Man, it feels like it's been so close for the past couple days! But I think I have most of the major stuff out of the way now, hopefully tomorrow is more rewarding.

[ALIHISGREAT]

i think one layer of aluminium should suffice for such a small disc... be sure to test the burst pressure at some point.

and how exactly are you planning to fuel??