Shotgun Design

[Nolo]

I'm working on an advanced shotgun design (and some accompanying rounds, and I wanted some input from all of you shotgun buffs on THR, as you would know the most about them and be able to point out any blatant (or not-so-blatant) mistakes that I may have made. Anyway here goes, pictures first, then technical descriptions:

This is the Werewolf 32mm shotgun. While 32mm sounds huge, it really isn't. The reason that the caliber is 32mm is because I wanted 12-gauge-like performance out of a much shorter shell, and, thus, the shell had to get wider. There are a few other advantages to this arrangement, I believe, such as better patterns (though I suspect that may only be pertinent to hunting and competition shooting, which is not what this weapon is designed to do) and a larger variety of exotic loads. Anyway, the shotgun is a semi-automatic, bullpup configuration weapon with a 12-round 32x44mm magazine. The entire weapon is roughly 600mm long and would be approximately 10 pounds unloaded, I believe. There are loading gates on both sides of the weapon and spent shells are ejected downward. Oversized shells are loaded through the ejection port under the weapon. The shotgun sports four Picatinny-type rails, three short and one full-length. The magazine is mounted overtop the barrel, between the dual cocking/charging handles. A safety has not yet been added to the picture. The weapon is mostly encased in a polymer housing for durability.

This is the basic 32x44mm buckshot shell, designed to simulate a magnum 12 Gauge shell. This version throws 14 triple-ought buckshot balls at roughly 1000 f/s.

This is the extended 32x51mm 000 buckshot round. It will throw 17 000 buckshot balls at roughly 900 f/s.

This is a special loading of the 32x51mm shotgun shell. It was especially designed for close-quarters combat against multiple enemies. The load consists of a rifled cylinder in front of a powder charge. However, the cylinder is diced into 64 small, unevenly weighted fragments. When the shell is fired the cylinder spins as a whole down the barrel thanks to the rifling, then, when the projectile exits the barrel, centrifugal force causes the pieces to separate creating a wide pattern much earlier than normal shells. This allows all the powder to burn in the barrel alongside increased expansion. In addition to the wide spread, the shell contains more lead than usual, further increasing the damage dealt to the target.

This is the concept for a rocket-propelled 32mm explosive fragmentation shell. Think FRAG-12.

Now, I've set out all these designs, but I think there are some problems. For instance, I think that, for some reason, I am throwing too much lead into the air with the shotshells. I have no idea why, as I calculated the volume of the round to be the same as a 3-inch 12 Gauge. Maybe I calculated wrong, I don't know. I also think that they may be going too fast (As far as I know, normal velocity for a 12 Gauge shell is ~1300 f/s), so I slowed them down a bit. I don't know.

Anyway, feel free to tear it all apart and criticize it off of the face of the planet, that's what I put it here for.

Thanks all.

 

[GunTech]

Before you do anything, pick of a copy of Swearengen's "World's Fighting Shotguns".

 

[Nolo]

"Get this book."
"Get that book."
Why don't I just buy every book in the world!?

Thanks.

 

[zinj]

Have you ever shot a shotgun before? I think you need familiarity with the type of gun; its strengths, weaknesses and applications before you jump in an try to improve it.

 

[Nolo]

Yes, zinj, I have shot a shotgun before. It's actually the only type of gun I really own. As well as my favorite type of gun. I've got a Mossberg Maverick 88. Cheap as dirt, that's why. Well, technically my father owns it, but it's mine, and will be legally when I'm 18.

 

[MCgunner]

Bullpups really suck for lefties.

 

[zinj]

OK, here are some criticisms:

1. Don't try to replace the 12 gauge. There is a reason it has dominated the market for over 100 years, and that is because it provides the optimum balance between power and controlability for most people. I'm pretty sure you went to the short and fat round to increase magazine capacity, but you are making the gun harder to load under stress (shorter ammunition doesn't feed as smoothly into a loading gate as longer rounds), removing access to a large supply of already made ammunition and components, and making box magazines more difficult to produce. And you aren't saving that much space either, an unfired 2.75 hull measures around 57mm.

2. 10 pounds unloaded is too much for a shotgun. For a short-barreled autoloader I would shoot for an 8 pound maximum.

3. There is no need for four rails on a shotgun (or a rifle for that matter, but that is another flamewar...). All a shotgun needs is a light mount, a bead or blade type front sight, and maybe a picatinny rail (for a simple reflex type site if using slugs) and folding rear sight. Everything else is fluff. Most situations within a shotguns effective range can be handled by just a bead.

4. There isn't enough gripping area for the forward hand. The gun will be hard to control.

5. Bullpup shotguns have been produced before, and they have pretty much universally been failures. There is a reason why shotguns have stocks shaped like they are, and that is because that particular design minimizes recoil and keeps the gun controlable.

6. If this is a combat shotgun it should have a box magazine. Tube magazines are nice, and quick to reload, but detachable boxes can keep up a much greater rate of fire (at least until the magazines are depleted).

7. Back to the 32mm ammunition: if those drawings are generally to scale, your wads are far too small. They would probably take most of the powder space if they were made to proper scale.

8. The "frag" shotshell doesn't seem to do anything that buckshot doesn't, except it will probably give a horrendous pattern and the fragments will quickly lose power as they spin through the air, sapping energy.

9. The place you have described mounting the safety seems to be an ergonomic nightmare.

10. Not to be a jerk, but it seems like you drew this gun first and then tried to describe it. You haven't stated how it is operated (recoil, gas?) or how any of the other internals work.

I have some more criticisms I may post later, but these are the ones that jumped into my head.

If you are really serious about create a shotgun you need to recognize three key aspects that dominate design:

1. Recoil and how to minimize it. Despite all of the hype about magnums and super magnums, the 9 pellet 00 buckshot load at 1300FPS and 1oz rifled slug at 1600FPS provide all the power one can use and still remain controllable. Even so, these are pretty stout loads and a design needs to mitigate recoil.

2. Simplicity is god. Anyone can make something complex, but it takes a genious to make something simple. Simple things are more reliable, easier to use, and easier to produce. There is a reason pump shotguns are still so universally popular today.

3. Don't try to make a shotgun into somthing it is not. As shotgun is ideal for ranges inside fifty yards, 100 with slugs. It should not try to be a sniper rifle, or an artillery piece, or a machine gun. Again, pump shotguns are so popular because they are made for a purpose, and they do that purpose well.

 

[Nolo]

I'll respond point-by-point.
1. The basic load for this weapon would be 44mm long, which saves 13mm (I think that may even be too long). Also, I'm not too worried about box magazines. A shotgun, to me, is a different weapon than a rifle, and I think that it is better suited to tubular magazines, which was the whole point of this design: to reduce the overall length of a tube-fed shotgun.
2. I based the weight of of an unloaded AA-12 shotgun. Maybe I was wrong in doing so. But I figured a similar composition, action and basic function, which is why I did it.
3. You're probably right. That's just how this picture turned out.
4. I worked and worked on that. I think you're still right. It was one of my big problems with the design.
5. I don't see any fundamental reason why bullpup shotguns have to fail, which is why I went ahead. But yeah, all the ones that I know of sucked.
6. Again, I kinda designed this weapon specifically for a tubular magazine, whether that was the wrong direction or not, I don't really know, but that was the course I took. I would like to point out that having this be a payload weapon was a large part of that decision. As in, I wanted to be able to easily load exotic grenade, rocket, transmitter, etc. rounds without having to interfere with the magazine.
7. I don't understand why the wads are "too small". Why do you need the dead space? This is an honest question. There's probably a really good reason for it, and it would explain a few discrepancies, but I don't know the reason and so I engineered it out.
8. The concept for the "frag" shell was to have extreme patterns at very short ranges. Maybe it doesn't do anything a regular shot load does, but oh well.
9. I never described mounting the safety, I don't think.
10. No, it's cool. I actually did all the internals first, then designed the package around it. The weapon uses essentially the same action as the Benelli Super 90, which is a kinda weird form of gas-operation. That's not to say there might not still be some issues there, there usually is until about the third draft of the design.

All three of your last points are duly noted, thank you.

Thank you very much, zinj, that was very helpful.

 

[PumpactionPimp]

shot gun crazy

where can I find a short barreled shotgun aka doubble barelled "coach gun"
for real cheep (prefered W/hammers) stoeger is too expensive?

 

[zinj]

Well, I guess I'll do the bulleted list thing again:

1. Again, I would say if you want high capacity use a box magazine. You said this is going to be a "payload gun," well making the shells that short means that the payload is going to have to be short as well (hell, it might be wider than it is long!), and that will give you poor aerodynamics and can easily lead to tumbling.

2. I wouldn't base anything in a design on the AA-12. Essentially it is a large, impractical, fully automatic toy.

3&4: Well, we agree on something!

5. This isn't my area of expertise, but I conjecture that a shotgun recoils less with drop in the stock for the same reason "Plowhandle" single action revolvers kick less, namely that some recoil energy is converted to muzzle flip. While trying to eliminate muzzle flip is nice on a small bore rifle, in a paradoxical it way helps keep a heavy recoiling shotgun more controlable.

6. I think we are going back to "A shotgun is a shotgun, not anything else." A tool that does many things often does them all equally poorly. If you want to make a weapon to launch payloads don't try to make it a shotgun. Again, these ultra-short shells you have would make producing payloads a bear. It isn't like a payload weapon needs a high capacity anyway.

And if you are making a payload weapon don't try to make it semi-automatic. It won't be able to cycle all of the different loads you would shoot out of it.

7. If you cut apart a shotgun shell you will notice that there are two parts to the wad, a shotcup and an over-powder wad. In these diagrams you only have the shotcup. Off the top of my head I can say that an over-powder wad is needed to seal the bore and cushion the shot against acceleration (to prevent them from getting deformed and blowing the pattern).

8. Spread is really overhyped. The reason that buckshot's spread is so effective is not because it makes it easier to hit the target, but rather because the multiple projectiles increase the chance of hitting a vital system.

9. I must have been half-asleep last night, I misread the magazine location as that the safety would be mounted "overtop the barrel, between the dual cocking/charging handles."

10. The Benelli action doesn't work well at all with heavy guns (this is why their M4 is gas operated). Recoil actions in general are rather finicky with what they cycle (and I say this as a Browning Auto-5 lover), a modern gas action is far more versatile.

I also this your feeding system is overcomplex. Instead of mounting the barrel under the mag and trying to have two feeding ports to make it ambidextrous, I would just do something similar to the Ithaca design (mag under barrel, split carrier drops down from bolt to eject empty and load fresh shell). I'd imagine trying to feed a shell down from a magazine while not simultaneously ejecting it could get over-complex.

 

[Nolo]

1. A box magazine is fine, but I think there's something to be said for the ease of refreshability that a tube magazine has. And the payload rounds wouldn't be as short, as they would be loaded directly into the breech.
2. Oh, it wasn't based on the AA-12, just a weight estimate.
3&4 is okay.
5. You may be right. In fact, you probably are right.
6. You're correct, but I think that a shotgun that has a larger bore for the same power get better performance anyway, no?
7. I know. I have no idea why the over-powder wads weren't extended.
8. Nice point.
9. Hahahaha! Oh, that's funny! I'd never put a safety there!
10. Hmmmm... Internals redesign, here I come!
True... Thank you for all the input, zinj.

 

[Bad Penny 03]

"Rifling" on wadding will not do anything.
Foster slugs with rifling on them are mostly for looks.
In practice they really don't make the slug spin that much, if at all.
The squared off pieces of lead , much like a brush load or old fashioned cubic shot, will do more to open up the pattern than any rifling on a slug or in this case the wadding of a shot load.
Firing shot through a rifled barrel produces a donut like pattern. Something I would avoid in my combat shotgun.
You'd be better off with a duckbill choke.

Short wads tend to flip over in the bore breaking the gas seal reducing an already low chamber pressure. This can cause your load to sound like a 40mm blooper, throwing lead down range at less than ideal velocities.
One of my favorite loads, the Remington 3in magnum #4 lead buckshot load (41pellets) doesn't seem to have this problem. This would be a good place to start for ideas.

32mm would be a problem.
The increased volume of the larger bore would necessitate an entirely different powder. Keeping the pressure safe through the burn cycle , while still maintaining chamber pressure high enough to create the desired velocity and not make recoil less than ideal would be an R&D PITA.

Maybe this one should stay in the realms of HALO and comic books.

 

[Nolo]

The 32mm Frag shell doesn't have a wadding. It is just a rifled, diced cylinder.
Otherwise, good points. I'm working on a 12 Gauge shotgun now.

 

[Bad Penny 03]

Yeah, I didn't mean it like that...

 

[MAX100]

You probably have a great future ahead. You are trying to hard. Keep your design simple, compact, lightweight, easy to disassemble and low cost to produce. Try to keep the retail cost of your shotgun design around $600. Stay with 12ga shells. There is plenty of time later on to adapt your design to a new shot shell.

If you do a pistol grip design make it a free pistol grip not a thumbhole type.

How many times have we all seen a great design that was very simple, and made you say, "I should of thought of that". The simple ones are the ones that last.

Bullpup designs look cool but they are blocky and wide vertical. Unless you can meet the above criteria it will be dead in the water. No one will want to manufacture it.

Look at the AK47, simple, easy and low cost to produce, can adapt it to many calibers, even shot shells.

If you can meet the above criteria you may find your design in the hands of the US military one day.

GC

 

[The Deer Hunter]

10. No, it's cool. I actually did all the internals first, then designed the package around it. The weapon uses essentially the same action as the Benelli Super 90, which is a kinda weird form of gas-operation. That's not to say there might not still be some issues there, there usually is until about the third draft of the design.

My M1-S90 works solely on recoil...Well, at least mine does...Along with not using gas, the bolt has a buffer tube that extends into the stock.

Also about the 32mm, 12 GA can keep things cheep(in terms of ammo...)

You make it clear that you want a tube fed weapon, the Neostead shotgun has a unique loading system you might find interesting. The side by side magazine tubes flip up at an angle so you can reload faster.

Neostead:
http://world.guns.ru/shotgun/sh08-e.htm

Its still wicked cool looking.

 

[Nolo]

Yeah, I didn't mean it like that...

Not sure what you mean.
I will change the wads.
I think I'm going back to 12 Gauge, anyway. It was a novel idea, but it didn't work out.
Thank you, MAX100.
The Deer Hunter, I'm sorry, I meant the M1014, not the Super 90. It was a misprint.