BACH – Bolt Action Cartridge Hybrid

[LCTChamp]

Oh you said you were considering making something like this so I thought you were referring to a hybrid.

Back on topic: If you could possibly make the cartridge a little bit longer then that would increase power.

[sputnick]

noted, Im really looking forward to making something like this, i was thinking something like 1 inch chamber by maybe 3-4 inches, then a barrel of about 3/4 or 1/2 inch, most likely 1/2 inch to get a better ratio, but i am definitely going to copy your idea of the stock, but iv decided the best idea for the mechanical punch is going to be a bolt that slams forward to slam the cartridge against the barrel

[Lentamentalisk]

Daccel, this looks incredible. One quick question. You mentioned an integral suppressor, but I don't exactly see anything, so am I assuming correctly that the barrel diameter is actually substantially smaller than what it looks?

The general rule of thumb for hybrids, is that [chamber volume]x[mix number]>[barrel volume], though far more important is to experiment around on HGDT. Make sure to take full advantage of the "Sensitivity" function, to see how important each individual factor is.

edit: another important note. Having a consistent, strong burst disk, is incredibly important for hybrids. The maximum pressure that they can get is limited by the burst pressure of the disk. In order to get stronger burst disks, try using aluminum tape, the kind that David Davini (sp?) uses on his pneumatic cartridges. Also, try laminating foil with tape, and other such things. Water bottle caps have been used, and all kinds of things. Just experiment around, testing all of their burst pressures, and how cleanly they burst, until you find something perfect for your desired pressure.

[daccel]

sputnick - If you search for pneumatic cartridge, you will find it has already been discussed. I'm sure those threads will have enough info to get you started.

lctchamp - Unfortunately for making a longer cartridge, the barrel is epoxied in place and I would also have to cut the breech larger. I think I will leave things as is just tweaking to maximize the potential and expand my hybrid knowledge. And instead integrate any major changes into the next design.

Lentamentalisk - Yes, the outside tube acts as the receiver for the bolt and cartridge and the front part of it forms the outside of the suppressor - see specs in original post. I used tape to center the barrel then epoxied it in place. The volume of chamber, barrel and suppressor are 1.1, 4.6 and 3.5 cu in, respectively.

Great tip about the sensitivity function, I hadn't seen that before.

Also a good point about the burst disk strength, like I said I noticed a huge difference moving to the aluminum can disk. I will try layering that and see how many it will burst.

[sputnick]

I know there are many discussions, and I already have a good idea what i am doing, I am just commenting on what changes i am making.

[mega_swordman]

Congratulations on getting it to work, I have a few questions though. Would you mind posting a close up of the bolt itself? I can hear the cartridge snapping into the bolt but an not sure what exactly is happening there.

Also, why did you decide to drill holes at the epoxy fittings? Do they serve any purpose?

Thanks.

[jackssmirkingrevenge]

omg it works! very nicely done

Now let's see a working extractor/ejector on the bolt

[Lentamentalisk]

Wow, JSR, you are living proof that no matter how awesome you make something, you can never keep people impressed for more than a few minutes...

[jackssmirkingrevenge]

Wow, JSR, you are living proof that no matter how awesome you make something, you can never keep people impressed for more than a few minutes...

That's truer as time goes by and directly proportional to your knowledge in the relevant field. The sun has gone from big fiery sky god to annoying source of UV radiation in a matter of centuries.

In this case, I am genuinely impressed by what daccel has done so far, but why should I encourage him to rest on his laurels when the design has so much more potential?

[starman]

daccel, very nice work on this hybrid project...inspiring indeed.

Do some calculations with HGDT. You'll find you don't necessarily have to use terribly high psi rated burst disks to get great performance. You'll get some more performance but at a cost of diminishing returns

[daccel]

Thanks guys.

The sound isn't actually the cartridge snapping into the bolt, but the breech. I left it slightly smaller than the cartridge so it couldn't just fall out. The bolt is quite basic so far, but here's a pic anyway.

The holes are to increase the strength of the epoxy joint. I hydro tested a similar chamber and it failed at 3300 psi, but held with the holes drilled. Figured I might as well play it safe.

Easy Jack - extractor/ejector is in the works. I wanted to focus on the loud stuff while I have a rural test site visiting my parents. Don't think firing a hybrid in my apartment in the city would be much appreciated . And after seeing success with this the dream of an auto cartridge is a bit closer...

[jackssmirkingrevenge]

And after seeing success with this the dream of an auto cartridge is a bit closer...

Indeed, making a semi/auto direct blowback design would actually be much simpler to conjure up than bolt action. All you need is a spring loaded bolt behind the cart with an off-centre projection that would tip the cart out to one side once it's clear of the breech, as I had done with my combustion cartridge.

[ALIHISGREAT]

How did you cut out that bolt and receiver Daccel? a dremel?

[daccel]

I think on very low mixes, the inverse is probably true, but when you start trying to contain high mixes and have to basically replicate a firearm bolt and lugs, then absolutely. The more I think about it, the more it makes sense to leave a single shot cannon to the pneumatic realm because consistency and subsequently accuracy would be much easier to achieve that route, whereas an auto usually isn't intended for the same level of accuracy. Unless you're going for raw power, then have at'r.

The downside to an auto hybrid cartridge is the time involved in making and charging multiple cartridges, though this would be clearly offset by the sheer cool factor . And if anyone has an airsoft shell they want to donate to that project...

But I will try to get an extractor working on this so I can call it complete.

The cut on the bolt was a chop saw. For the receiver I drilled out the bulk of it and then finished it by eye using a rotozip bit in a drill press. In retrospect, it would have made sense to make the straight cuts on the receiver with the saw. Sometimes I miss the obvious . But I don't see any reason you couldn't do it with a dremel or drill, it would just take longer. A carbide bit would make life easier.

[Lentamentalisk]

Just a thought for fueling many cartriges at once, is that you could make some sort of fueling station, involving a high pressure storage tank, (ie: old CO2 tank or the likes), a regulator, and female shrader valve (maybe just a press on one like they have at gas stations?). Fill the storage tank with the correct mix, dial the reglator to the correct mix, and then just in cartridges, one at a time, to fill them up nice and quick. A CO2 tank could handle a high mix explosion fairly easily, as CO2 can often get up to 1200psi when it gets hot, so as long as you stick below 15x in the storage chamber (remember it will have to be substantially higher than what you intend to use the carts at, because the pressure will keep on dropping) you should be fine.