44 replies to this topic

[Ambience 327]

I am working on a homemade that will be integrated into the shell of a Double Shot. Rest assured that this is not just a concept thread - I fully intend to build this and already have the shell and some of the materials. I am just hoping to get some comments on how difficult my trigger & valve mechanism will be to build and maintain, to decide if it is worth it to keep the dual-stage functionality rather than just going to a single tank & trigger that will fire both barrels each time. Since I am on a limited budget for this, "try it and see" is not my preferred method!

The image below outlines what I am trying to accomplish for the airtanks and trigger/valve system for this gun.



Basically, the pump will be housed either in the space below the barrels, or below the handgrip, depending on if I can get one to fit inside the shell or not. The pump hose will be split between the two air tanks, and a valve will be attached to each air tank with a two-stage trigger similar to what is already in place on the Double Shot. (If you are unfamiliar with the Double Shot, basically a partial pull will trigger one barrel, allowing a second pull to trigger the second, or a full pull to trigger both at once.)

Since I have not yet tackled any homemade projects yet, I would like any feedback about potential trouble spots with this design, as well as any ideas for something to serve as my air outlet at the end of the system. Basically, after the valve releases the air, it reaches the breech location, where the Double Shot's barrels break away for loading. I am currently considering using the existing outlets from the Double Shot, and just connecting my tubing to that with epoxy or plumber's goop, then using a foam gasket to get a good seal between the outlet and the barrels when they are engaged. (The barrels will be replaced with either nested brass or CPVC, allowing a shell-less rear-loading system that keeps the Double Shot's breakaway loading intact, without the annoying shell ejection.)

Also, the image shows the inlet from the pump to the tanks being on the opposite side from the outlets to the valves. Would it be too much stress on the endcap to have both the inlet and the outlet in the same endcap? That would reduce the amount of tubing required, and make it easier to get the whole assembly to fit into the shell.

Edited by Ambience 327, 27 August 2008 - 10:17 AM.

[Split]

Good ideas. Simple solution: make your dump valves' travel distance different. If one has 1/4" longer travel distance, it will trigger 1/4" later on the trigger pull (for good sound reasons, leading back to you using solid rods to connect giving a push/travel ratio of 1:1 [yes this is under ideal conditions, but any thermodynamic and other changes are negligible]).

Can I make a suggestion? Now I've never used or owned a double shot, but from what I remember it has a spring actuated latch that hooks on to keep the break away barrels closed. Perhaps you could attach two small pieces of brass, 1/16th" greater diameter than that of your barrel to this latch. This way, when the gun is closed, they nest the barrels for an airtight seal, and when you need to break the barrels down, they slide back off of the barrels as you open the latch.

To connect them to the output of your tanks, put some pieces of brass with the same diameter of your barrels for these latch piece to slide along, and connect the air outputs to those.

[Gyrvalcon]

You're going to need a couple check valves before the air tanks, or else you'll dump both tanks when you fire the first shot.

[imaseoulman]

You're going to need a couple check valves before the air tanks, or else you'll dump both tanks when you fire the first shot.

Actually, he only needs one check valve- on the one that fires second.

Ambience-
I see a limiting factor in your air flow between your tanks and dump valves. If that tubing is not at least 1/4" ID, then you won't get enough power out of your blaster. A simple solution for this is to connect the dump valve directly to the tank. Pressure rated tubing with 1/4"+ ID isn't too cheap (but not super expensive either, and for the quantities you need, about 1', you're probably fine).

Also, I know the drawing isn't to scale or even appraoching it, but I see that you have your cable connected in two different places. What you probably want to do is connect them at the same place on your trigger, and make one cable slightly longer than the other.

Do you already have a dump valve picked out? Before choosing one, make sure you can open it with your planned method. Opening dump valves via a wire cable isn't always the easiest thing to do (it takes quite a bit of force).

[Ambience 327]

Good ideas. Simple solution: make your dump valves' travel distance different.

That is basically the idea - and is what I was trying to get across with the two different attachment points on the wires. That is also basically how the DS works now - it has two different barbs on the trigger assembly that hit the plunger releases on the two plunger tubes at different times.

Can I make a suggestion?

You can - and I really like it. If I can figure out how to do that without too much extra expense/work, consider that added. The seal between the outlet and the barrels is a primary concern for this gun. I hadn't even considered anything remotely like that. Did that thought come from your work on the Vulcan?

You're going to need a couple check valves before the air tanks, or else you'll dump both tanks when you fire the first shot.

I told myself the same thing when I was describing the idea to my wife later in the day after posting this thread. Thanks for pointing it out though - if I hadn't thought of it, it would have been a real sticking point in the design - probably requiring an extra trip to the hardware store at best (or another week of waiting for a shipment at worst).

Actually, he only needs one check valve- on the one that fires second.

Which was my second thought after realising I'd need check valves.

I see a limiting factor in your air flow between your tanks and dump valves.

Noted. I hadn't considered that. I'm not sure how big my tubing will be yet. It will take some measuring and thought to make that decision. I haven't dabbled much in this stuff yet, so I didn't know you could attach the valve directly to the tank. I will definately consider that when I begin refining my designs.

Do you already have a dump valve picked out? Before choosing one, make sure you can open it with your planned method.

Nope - I want a more finalised design before I start shopping for check valves. I'll need to know things like the amount of space I have available for the valves, where they will sit, etc. I will definately work on the trigger mechanism's feasibility and reliability - I'm not dead set on using wire. One of my main concerns is a fairly easy trigger pull (for a full grown adult anyway). If this thing gets decent ranges, it may become my primary.



Another thought I had was the question of being able to re-pump when only one barrel has been fired. If I am using a bicyle/sports pump, it isn't going to have an OP valve on it - will the check valve ensure that the all of the new air pressure goes only to the depleted pump, or will I need something else to make that work?

[Split]

Actually that thought came from working on my current project. But, like Angel, I find it never helps to talk about them before they're done. You should see it soon enough. Angel actually knows about it. He seemed pretty enthused.

Edited by Splitlip, 29 August 2008 - 07:18 PM.

[imaseoulman]

Another thought I had was the question of being able to re-pump when only one barrel has been fired. If I am using a bicyle/sports pump, it isn't going to have an OP valve on it - will the check valve ensure that the all of the new air pressure goes only to the depleted pump, or will I need something else to make that work?

Not a problem. Here's what will happen:

After firing the first tank the other tank will remain pressurized (because of the check valve). If you don't need to fire again right away and have time to reload the other barrel. Just pump it to the desired pressure. Air won't be forced into the second tank until the pressure of the first tank is equal to it.

Did that make sense? If not, here's a quick example:
Let's say you pump the blaster 12 times and it reaches about 35 psi, and say that's the pressure you want. That pressure will be constant everywhere from the end of the pump (assuming it has a check valve built in, which they pretty much all do) to the start of the dump valve. After you fire the first tank (assuming you have a check valve in place for the second tank) there will be normal pressure (equal to the atmosphere) in every part before the check valve. Everything between the check valve and the second dump valve will still be at 35 psi. Now let's say you pump two times. That will pressurize everything before the check valve to say 12 psi but everything after the check valve stays at 35 psi. No more air can get past the check valve until the pressure behind it equals the pressure in front of it. So let's say you pump four more times and there is now 35 psi throughout the system. Only if you continue to pump will the pressure in the second tank increase. Say you pump twice more and the whole system is now 40 psi.

If that doesn't make sense, then well, I'm not sure how to make any more sense without an animated diagram which I'm not going to do. Point is, you can fire once and pump again (about half the times you did to pump both tanks), reload and fire again.

[imaseoulman]

The single check valve actually gives you an additional firing mode: when both tanks are pressurized, you will have the option to dump one at a time, or both at once, depending on which barrel you choose. Potentially you have an occasional longer-range shot, by giving up the quick second shot.

This would only make a difference if both dump valves went to the same barrel.

[Ambience 327]

Did that make sense? If not, here's a quick example:

That is what I thought would happen, but I wanted confirmation. That you have supplied, and you have my thanks. So basically the check valve completely solves that issue.



At this point I am thinking put a check valve on one tank, attach the valves directly to the tanks, and use the outlets from the Double Shot's current plunger assembly. Then I just have to make sure any tubing between the valves and the outlets is sufficiently large and pressure-rated, and work on the seal between the outlets and the barrels, and this thing will be ready for production.

Now, if I can just find a two-stage bicycle/sports pump that is small enough to fit in the false "pump action" area underneath the barrel assembly, I'll be all set. (I want two-stage to reduce the total number of pumps to prime the gun - I'm going for maximum efficiency here since the gun will have a built-in break-action breech. It should be fairly practical for a war, especially backed up by a nice NF or Disc-Shot as a side arm.)

[imaseoulman]

One quick comment, the thickness of tubing is no longer an issue if you attach the dump valves directly to the tank. The air rushing out won't be restricted by the tubing (it will be emptying from the tanks) so the limiting factor will be how fast the dump valves can release air. Good luck with the pump!

[Ambience 327]

Duly noted. Thank you for your help imaseoulman - this is the kind of input I was hoping for when I posted the thread. Anything to keep costs down is a good thing, seeing as the only money my wife will let me use for this is money I can earn from Ebay sales. The input I've gotten from you guys will definately help avoid a lot of trial and error style research.

If this thing works as well in the real world as it does in my warped mind, I will really enjoy it. Before the stupid things broke, my two Double Shots were my favorite guns in my arsenal for our indoor wars with the youth group at my church. They are just so comfortable, and the two shots before reloading was great. The only problems I ever had with them were the reload time and the whole shell ejection deal - both of which will be improved with this mod. The ranges were good enough for our indoor wars (mostly stock or simple AR removal guns), but I am starting to take an interest in some of the nearby wars that I've heard mention of on this board, and so I'm going to need something with a little more kick. I figure if I can get something like 80-100 feet flat & accurate with each barrel in single-loaded mode, it will keep me competetive.

Part of the idea is to be able to shotgun load one or both barrels as well - either with streamlines, micro stefans or 1" nano stefans. This will be fairly easy with the break-action breech, and with the power I'm gueesstimating for this thing, I should see a halfway decent range for a shotgun load as well. I'm thinking the ammo holder in the Double Shot's stock will be a great place to keep 1" nanos, and I can carry stefans or streamlines more conventionally (pockets, ammo holders, etc).

[CaptainSlug]

This may be stating the obvious, but you could always just have two triggers and one check valve inbetween the pump and each tank.

[Ambience 327]

I want to keep the single trigger that the Double Shot currently uses. I find it comfortable, and it souldn't be too difficult to make it work - pull ~1/2" for first shot, pull full 1" for 2nd shot. Something like that should work without too much effort.

one check valve inbetween the pump and each tank

You lost me there CS....? What would that accomplish that a single check valve on one tank (after the "T" splitter) wouldn't? Of was that part of the two-trigger idea?

[CaptainSlug]

one check valve inbetween the pump and each tank

You lost me there CS....? What would that accomplish that a single check valve on one tank (after the "T" splitter) wouldn't? Of was that part of the two-trigger idea?

It's part of the two trigger idea because you wouldn't want to have to remember which trigger needs to be pulled first.

[imaseoulman]

Yeah, Slug's right. It would work with only one check valve and two triggers, but you'd have to make sure the check-valve-less (I like that word ) trigger got pulled first.

On some of my projects I didn't worry about that because I know my gun well enough to know which trigger to pull, but it's always better to not have to worry about firing order. As far as check valves, I don't think I mentioned it, but if you're looking to save money, this is probably your best option:

mcmaster.com part# 7757K11 $3.23

other useful parts:
barbed tees (pack of 10) 5463K353 $7.37

barbed connector (pack of 10) 5463K333 $4.74

tubing 5233K52 $.10/ft

instant tube fitting 9087K61 $2.14

If you're just going for cheap, there are some barbed fittings available slightly cheaper, and they usually get the job done just fine, but occasionally I've had minor problems with them (nothing that a zip-tie couldn't fix).
Cheaper barbed tees 5116K13 $3.22 (pack of 10)
Cheaper barbed connector 5116k18 $2.37 (pack of 10)
These should do the job just fine.

Good luck getting all of this put together. I'll be interested to see how you fit it all together!

[Ambience 327]

Unless I attached both tanks to one barrel, I don't see how that would be an option in any case...?


The only way (with my airtank set-up) that I could achieve that would be to not have the check valve, and only pull the trigger partially (for a single tank to go). Then all of the pressure in both tanks would go out the single barrel. But that would make it impossible to do the semi-auto firing that I'm after in the first place.

Edited by Ambience 327, 12 August 2008 - 06:05 AM.

[Ambience 327]

Ok - now I see what you are saying. It just wasn't clicking in my head. Now it has.

It is definately worth considering, but I think I really want to stick with the single, two-stage trigger system as-is. It will be easier to engineer, easier to use (in my opinion anyway), and if I can squeeze 80+ feet out of each barrel, it will be powerful enough for me. The additional power provided by the second tank just isn't all that desirable to me - it doesn't fit my playstyle.

Rather than taking long-range pot shots, I'd rather rush, or be rushed. I just find that more fun - the thrill factor makes it worth spending money on this hobby. I can see me keeping one barrel shotgun-loaded with nano stefans (the 2nd barrel in the sequence) while keeping the other (primary) barrel single-loaded. That way, I can pop of a single shot, re-load and re-pump as time allows, and keep the shotgun barrel loaded for rush/anti-rush duty. Pair that with a Nitefinder or Disc Shot sidearm, and I think I'd have all the firepower I'd need to suit my play.

[Ambience 327]

Double-Posting to bump and get a response to some new questions.


I have done a lot of work on paper, in my head, and on the McMaster Carr website (thanks for the links imaseoulman, a lot of those items will probably become a part of this project) and I think I have the design mostly completed now.

I do have a few additional questions right now:

1) Probably the most important: I have yet to find a valve suitable for my needs. I need something moderately inexpensive (I have to buy two of them), it needs to be able to be actuated by either cables/wires/fishing line, a solid trigger bar, or something similar - I don't want the valve actuators showing outside the gun. (I want it to look like a normal Double Shot for the most part - the only thing showing will be the pump handle as I can't hide that.) It also needs to be fairly small - maybe 1" or slightly larger in diameter, and not too much longer. If you know of any valves that meet these requirements, please share your information with me.

2) How do I connect the tubing to my air tanks? Should I use barbed connectors or maybe instant fittings and just epoxy/goop those into a pre-drilled hole in the endcap? If there is a better way, please share. (I'm hoping to have the inlet tubing and the outlet valve connected to the same end of the airtank if possible, though it isn't completely necessary - but it will mean less bending of the tubing.)

3) On a related note, how do I connect the valve directly to the tank? Do I just make a hole the proper size and epoxy/goop the thing in there, or is it more complicated than that? (The answer to this may rely a bit on the answer to question # 1.)

Edited by Ambience 327, 15 August 2008 - 01:51 PM.

[Draconis]

You know, this whole project sounds like something that would work very nicely with two Big Salvo blast chambers and a modified trigger assemblyfrom either a BS (only have to buy and destroy one gun), or a SMDTG.

[Ambience 327]

The Big Salvo isn't the cheapest gun though. I think I can get all of the parts I need for less than the price of two BS's, and definately less than the cost of two BS's and a SMDTG.

Also, I really want to see what I can do with homemade internals. I'd rather do a bit of engineering here than just integrate some parts from other guns into it. It will feel more like my own handiwork then, rather than just a modification of somebody else's work. Not to mention the fact that BS's are prone to leakage and inconsitancy. I want something moderately powerful, but ultimately reliable. I think I can achieve this with PVC or CPVC airtanks, a few valves and some tubing - lovingly crafted together into my own dream gun.

If somebody else wants to tackle a similar project with BS parts, fine with me - but I'd rather do it this way!

[CaptainSlug]

1) Probably the most important: I have yet to find a valve suitable for my needs.

And you're not going to. Valves are expensive and they generally are not designed for the kinds of flow rates you need for a project like this. Even the cheapest dump valves start at $10-$20 each.

2) How do I connect the tubing to my air tanks?

Barbed fittings will be cheapest.

3) On a related note, how do I connect the valve directly to the tank?

A threaded pipe nipple.

Edited by CaptainSlug, 15 August 2008 - 09:32 PM.

[Galaxy613]

The Big Salvo isn't the cheapest gun though. I think I can get all of the parts I need for less than the price of two BS's, and definately less than the cost of two BS's and a SMDTG...

You'll think so, but you'll be wrong. I was pretty shocked myself to see them going for $6.80 Almost makes me want to buy one. Or two.

[Shadow 92]

Here's a quick design I came up with. It's made mostly of PVC and hardware that you can get from Lowes or Home Depot. The trigger is a simple delay trigger, where when you pull it, it dumps the air tank to the right and if you pull it more, it dumps the air tank to left. The picture should explain most of the stuff.

[Ambience 327]

For various reasons, I am re-thinking my original stance of not wanting to use a Big Salvo or other air gun for this project. One of the main reasons was that I was misunderstanding the way the BS worked. I am now thinking of using a Big Salvo's internals to get what I am after for this gun. Another reason is that I have been told that guns with homemade parts may not be allowed at major wars. However, I need to know a few things first:

1) How big is each Big Salvo blast chamber? I need to know the length & diameter of the large cylinders that make up the chamber - to see if they would fit inside the Double Shot's available space (hopefully without losing the ammo storage compartment in the back). I am thinking I might need to stagger them to make it work, but a good idea of the space involved would help me determine if this is worth pursuing further.

2) Is it possible to modify the BS's trigger assembly to only fire off two blast chambers? I am still a bit uncertain as to how the trigger on this thing actually functions, so I don't really know how to accomplish this feat.


What I am hoping now is that I can squeeze two BS blast chambers into the Double-Shot's handle/stock area without affecting the external looks of the gun or removing the ammo storage compartment. I plan to run tubing from the blast chambers to the Double Shot's air outlet assembly, possibly incorporating the nested brass idea that Splitlip suggested.

The best part about this is, if I can get it working with the Big Salvo parts, then due to the fact that the Big Salvo has four blast chambers, I can make a second one of these if I can get my hands on a second Big Salvo trigger. With people making those Marvelous Salvos, that might not be too tall an order! (I'd want to get one working well before looking into a second one though.)

[Draconis]

1) How big is each Big Salvo blast chamber? I need to know the length & diameter of the large cylinders that make up the chamber - to see if they would fit inside the Double Shot's available space (hopefully without losing the ammo storage compartment in the back). I am thinking I might need to stagger them to make it work, but a good idea of the space involved would help me determine if this is worth pursuing further.

1.5" in diameter by 4" long. Including the hose nipple, but not including the barrel.

2) Is it possible to modify the BS's trigger assembly to only fire off two blast chambers? I am still a bit uncertain as to how the trigger on this thing actually functions, so I don't really know how to accomplish this feat.

You should be able to. It's mostly just a pipe with one end sealed by a rod with an o-ring on it, four hose nipples coming off of it, and the air inlet on the other end.

What I am hoping now is that I can squeeze two BS blast chambers into the Double-Shot's handle/stock area without affecting the external looks of the gun or removing the ammo storage compartment. I plan to run tubing from the blast chambers to the Double Shot's air outlet assembly, possibly incorporating the nested brass idea that Splitlip suggested.

Sorry, haven't had a DS open, but from the outside, it looks feasible.