An oddball shotgun idea

K

Krakerjax

Inactive
Salutations!

I come here seeking help with a rather odd brainchild I've been entertaining in my head. The thing is, i'm not sure if this is even the right place to post it, but as this seems to be a well educated gun forum, I figure it would be worth a shot.

My plan is basic. I want to build a shotgun. But not a traditional hunting one, it's for paintball. The problem is, regular paintball mechanic's don't apply as well as I'd hoped. See, I want this to be as close to a shotgun as possible, give or take a few adjustments for personal tastes and functionality. To do that, I need a clear understanding of how a pump action functions, which is why I'm here. Throughout the internet I've found bits and pieces of shotgun mechanisms. How the ejection port works here, how the trigger works there, but never all of it in one place that clearly explains everything I'm hoping to understand.

I know it's incredibly irrelevant to what is normally discussed here, but it seems that a gun enthusiast forum is the best place to seek information.

So, can someone provide some pictures or diagram of some sort that fully explains each step of a pump action mechanism, from the loading of the shell to it's ejection after the gun is racked please? :)
 
First, while it seems simple, a pump action shotgun is a pretty complex mechanism, and the idea of trying to build one from scratch gives me the willies.

Basically, when the gun is closed, the bolt is locked into the receiver. This can be done in a number of ways but is necessary to resist the backward pressure in thousands of pounds when the powder in the shell ignites. After the gun fires, the pump action moves an action bar backward, first unlocking the bolt, then picking it up and moving it to the rear. This action also cocks the hammer (internal or external) which has to be fitted with a disconnector so it will remain cocked even if the trigger is not released.

Then the action bar releases the magazine shell stop, releasing a fresh shell onto the carrier. When the foreend is moved forward, it moves the action bar forward, raises the carrier, and then picks up the bolt and moves it forward to push the fresh shell into the chamber. The last action relocks the bolt. In all this, the mechanism must make sure that the hammer cannot be released or cannot fire the round before the bolt is fully locked, no matter what the shooter does with the trigger.

Not simple.

Jim
 
a paintball shotgun? I imagine if it was easy it would have already been done. if it was something I had to have It'd be along the lines of a beanbag gun with pellets contained in a pre perforated ziploc or something
 
I saw a really cool air soft high end shotgun, that had 3-4 6mm barrels down the larger bored shotgun... the pellets loaded in tubes similar to loading tube mag guns, & the air soft shotgun fired the 3-4 pellets out of each barrel ( simulating buckshot )... it was realistic in weight & function... I'd think this would be a better starting point than a real shotgun ???
 
I have no idea how to do it... but as a guidepost for people who may have such know-how:
Normal paintballs are .68 cal, there are .54 cal available but not common.
The generally accepted safe fps is 150-300.
A remote air tank and line would probably be used.

FYI, I'm pretty sure just making it would be illegal. the BATFE considers paintball markers 'firearms' in the sense that you cannot make silencers for them or make your own without proper licenses/permits. Again, others here know more but I think what you want to make might qualify as an "Any Other Weapon" and require some sort of tax stamp. With ball bearings and significantly higher pressure it would be a very dangerous thing.

(per my very limited understanding of NFA laws...I stick to the legal stuff)
 
Jim, to be fair, I grew up as the son of a watchmaker. This is really more fascinating than complicated for me. Also, thanks for the explanation, that'll make it tons easier to convert it into a pneumatic system than it would be if I was just looking at some pictures.

Renfield, half the reason I'm doing this is because it hasn't been done yet! Its unique, and thus gives me a unique advantage while playing. Also, the shell it'll use is fairly simple, at least in theory. It's basically a regular shotshell, only instead of a primer, it's got wads that provide an air seal, so when the gun is fired, it pushes the wad and paint out all at once.

The only real complication I'll have with this in the long run is a matter of shells. I either have to keep collecting them when I've finished, or find an easy and painless method of producing them :(

Magnum, airsoft is fun, but its really easy to cheat in. You can't really pretend you didn't get shot when you get hit by the equivalent of buckshot in paint. Plus, my friends all play paintball!
 
I used to wonder why somebody hadn't used the 870 pump shotgun design as a basis for launching 40mm Grenades, if I die and go to Heaven I want one :D
 
SDC, exactly like that, only not at all.

That gun is basically the inspiration for doing this. I was looking for paintball shotguns and came upon the one shown in your link. I was quickly disappointed to find it was really just a fancy pump gun that shot 1 ball at a time. I wanted 5 or 6 at a time at the least, even if they had to be smaller caliber.

But to be fair, it looks cool.

To help people understand whats going on;

The reloading mechanism is simple, taken straight out of a pump action rifle, only slightly modified. From the tube above the barrel, a shell is pushed foward by spring. When the pump is pulled backwards, the shell is pushed onto a rack, which is being lowered by the movement of the pump. Simultaneously, the previous shell would be ejected by spring loaded latch located to the side of the ejection port, which would be opened with the movement of the pump. When the pump is moved foward the shell is pulled foward and down into the "firing lane", where the bolt quickly follows and locks it into place.

On the pneumatic side of things, it gets a little bit iffy. For a paintball gun to work, it needs to maintain a constant air seal. This poses a problem when intergrating with regular gun mechanics, because they don't require one. To accommodate this, a few creative adjustments had to be made. For starters, the bolt no longer had to house a firing pin, instead it would be a hollow tube with a cup seal fitted at the end of it to maintain it's seal for the durations necessary, along with 2 O rings. There would also be no hammer, instead it would be a simple valve body fitted with 2 cup seals and O rings on each end.

When the pump is in it's rest position, the bolt will be at the far end of it's throw, resting against what will eventually be a shell. The valve body will be adjacent to the bolt, maintaining its seal by means of a cup valve and a powerful spring keeping it in position. At this point, the air pressure would be against the valve. When the pump is pulled back, the bolt is pushed back, forcing the valve body with it, until it reaches the edge of it's throw, where it's locked in place by the trigger mechanism. The seal is now maintained by the force of the cup valve and spring on the locked body. When the trigger is pulled, the valve body is released, temporarily undoing the seal, allowing air to flow through the bolt to the shell, hopefully completing a shot, and then resealing itself by the power of the spring, effectively resetting it for the next cycle.


I've run it over in my head hundreds of times. There are things I understand in theory, but not in action, which is why I'm here. Hopefully, you can answer the multiple questions I'll have as I move foward :)
 
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can't say I have, though they seem to certainly have the knowledge I want to be looking for!


Thanks very much for the tip
 
If I'm not mistaken, a pump gun is normally loaded through the bottom, by a trap door sort of contraption, correct? I'm looking to reverse this and make mine top loaded. So below is my best attempt at explaining what I understand and what I think I need to do, hopefully you folks can offer some helpful advice.

From what understand, when a gun is first pulled back, the action bar on the bottom allows a shell to slide on top of it, and as the pump moves, the bar is raised by a small face riding along the contour of the action bar, which normally has a hump on the bottom of it, towards the back. My thoughts are if I mirror the action bar, and instead put the hump towards the front, as the pump moves back, the bar would be lowered correct? Thus allowing my shell to be prepped and lowered, preparing it for when the pump is moved foward.

When the pump is moved foward, I think a small lip normally pushes the shell up the action bar, into the chamber, where it's ready to be fired(I'm pretty sure the action bar then falls back down and allows a new shell to slide onto it). I figure this is something I can use essentially the same way. Simply putting a small arm along the pump bar would allow for the shell to be prevented from moving too far backwards, and provides a simple way to push it foward when the time comes.

The ejection I understand is a small port on the side of the gun that opens with the pump, and has a spring loaded flip arm that pops out when the gun is cocked, effectively ejecting the shell. I feel this can be duplicated and modified to fit the purposes in my gun.


Hopefully, some of you can decipher my post and offer some technical advice about my postion! Also, I'm sorry if you can't understand it too well, I'm not terribly good at explaining things that I understand only in my head. I'll try and get some neat pictures up soon!

P.S Would anybody happen to have some available information on how old-school brass shells were produced? It's highly relevant at the moment =p
 
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Why not just buy a used pump shotgun and some dummy ammo and study it? There is no point in trying to figure out how one works by looking at pictures and posting a lot of questions.

(No, the shell does not rest on the action bar; it never touches the action bar. Read what I wrote.)

Jim
 
If you're planning on firing MULTIPLE paintballs with each shot, that raises a new problem in regards to safety; you'd need some way of making sure that no more and no less than a specific number of pellets are loaded each time. Since you're allowing only a specific amount of propellant gas to be released each time, if you fired a shot that pushed only 1 pellet instead of (for example, 3), that would push the single pellet to a dangerous velocity (usually past 300 fps for a .68 paintball).
 
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