Ambidextrious Bullpup


December 29, 2003, 03:00 AM
Say I had a few million bucks to invest in the development of a rifle.

I want an ambidextrious .308 caliber bullpup semiauto. By "ambidextrious" I don't mean a reversable bolt like the AUG or FAMAS, I want it to eject downward or in some direction that won't hit you in the face, regardless of which shoulder you fire from. (This would solve one of the big beefs many have with bullpups).

I want it to be balanced so all the weight isn't in the stock.

I want it to be sturdy and reliable; able to withstand frozen wind or steamy jungles, and I want it to be tough enough to survive buttstroking someone with enough authority to actually hurt them. (Along those same lines, it would have a bayonet mount).

I want it to have quality iron sights built into the design (probably a carry handle type arrangement, like most bullpups) but also have a sturdy mount for optics. Ideally I'd have an ACOG scope that was mounted in such a way that I could also use the iron sights; a see through mount. A raised cheekpiece would be built into the stock.

I don't want the length of pull to be too excessive; many bullpups seem built for people with ape arms.

Barrel length should be a full 20-22" while keeping the overall length under 40".

The weapon should have provision for mounting a bipod that does NOT hang off of the barrel (like the FAMAS bipod, for example).

SO....! Who else would want one?

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December 29, 2003, 03:32 AM
SO....! Who else would want one?

I'll take one. You payin'?!?!?! :D

tire iron
December 29, 2003, 12:06 PM
I think you pretty well have it covered.

The only thing I would add is a button up by the trigger that was connected to the magazine catch - so one could 'dump' an empty mag with the 'strong' hand while the weak hand goes for a full magazine.

The way other bullpups work these days is one's hand MUST go to the magazine location with the weak hand and manipulate the magazine catch and extract the magazine. This works fine when one has the time to do that - but it not the fastest way to change mags.

Great idea - but I won't hold my breath on this one.


tire iron

December 29, 2003, 12:11 PM
Night, you have got a couple of things standing in your way from a design perspective. (and as you know the behind the scenes you know I've put a bit of time into this thought process!) :)

The crime bill kind of screws up domestic designers because we need to design around existing magazines. Right now the most affordable .308 magazines out there are for the FAL. So if you design something that takes FAL magazines it needs to be a rock and lock kind of system as opposed to the straight in, straight out (AR mag). So you need to have room in the LOP for the long .308 length receiver, and you need the pistol grip far enough forward that you still have room to rock the magazine forward into place.

Downward ejection probably ain't going to happen with a .308 bullpup. You can do forward ejection, but that requires some serious from the ground up design and some super dooper machine time. :p If you were not limited by the crime bill you could design a pan feed or something P90 like that would sit ontop of the action, but then you are dealing with the large size of the .308 round.

My first .308 bullpup prototype was downward ejection. However it was only an 8 shot design. It was based on the M1 Garand action, only flipped upside down. You inserted the En Bloc clip through the bottom of the buttstock, and ejection was downwards. The reason I shelved it was because the line of sight was massively high above the bore. ( take your Garand action out of the stock some time, flip it upside down, and place your cheek above the magwell and you get an idea of what I was seeing). I tell you that you feel really stupid after about 20 hours of coming up with a good trigger pull for an upside down bullpup Garand only to realize that the thing is pretty much useless anyway. :D

So to reach your stated goals your best bet would be forward ejection, and a AR10 style magwell. LOP is still going to be a touch long. Measure a .308 receiver and you can see what I mean. Forward ejection can be achieved through the use of a casing lifter during extraction, then as the bolt travels forward it gets shoved out the front of the action. (like the FN2000)

Now to do this you are going to need to design the action from the ground up. That is where the cash comes in. If you happen to have an extreamly large chunk of money laying around somewhere just let me know and I've got the blueprints around here somewhere. :)

Andrew Wyatt
December 29, 2003, 12:27 PM
What about having the magazine location be 30 degrees from vertical, with two magazine wells. the weapon ejects downward. to change sides, remove the magazine and install it in the other magazine well. alternatively, you could go with a rotary magazine design like the johnson. put the magazine atop the weapon, and feed the strippers through the top or side.

while you're at it, can you build me a mini-14 with a johnson style rotary magazine?

December 29, 2003, 01:29 PM
Offset magazine, eject downward to side of magazine.
Their you go, ambidextrous. Needs some R&D.

Trigger? Why not use an "electronic" trigger that creates a charge in the same way fireplace lighters work when you pull their triggers? Just find a way to route that to the primer through the firing pin and boom. Instant lock time with the trigger however you want it. Of course, it would be semi and you would have to worry about grounding out and water.

I thought of a good trigger linkage a long time ago involving R/C car ball joints, and plastic end caps. Almost NO play if you used metal ball joints and the captured them with a nut. Also, trigger could by adjusted by turning the tie rod connected to both caps and making it shorter or longer, thus the amount of pull required would be shorter.

I know you have absolutely no idea what im talking about.
It makes sense in my head, all of it!

December 29, 2003, 01:48 PM
I like the idea of a ball-jointed trigger linkage setup with a turnbuckle thrown in for adjustment. The pivot points have to be tight, though or the whole setup will be sloppy.

Why not a 7.62x51 version of FN's F2000? It ejects spent cases forward, so it would be equally friendly to all.

Andrew Wyatt
December 29, 2003, 02:06 PM
forward ejection = evil.

if you have a stoppage, you have to dissassemble the gun to clear it.

December 29, 2003, 02:22 PM
Is there any reason you couldn't, as was suggested, put a downward ejection port right next to the magazine well? (The mag well'd be funneled so you wounldn't be trying to stuff the fresh magazine into the ejection port during a quick reload).

The weapon would have to be a little bit wider, but it wouldn't matter any, really.

Take the M249 SAW, for instance. When using the M16 magazines (assuming it works), it feeds from the lower left and ejects to the lower right. You could probably rotate both the magazine and the ejection so they're vertical. It'd require a well-designed ejector, though.

George Hill
December 29, 2003, 02:22 PM
Other ways to look at it... Instead of a pan style mag system like a P-90 or a Lewis... why not a rotary mag like a Calico or Bizon? (just use flat nosed bullets instead of sharp points)
Hmmm... then you would have that high sight problem that Correia already mentioned with his inverted M1 system.

To be truthful, I really don't see the advantage of requiring a down eject.
Just make the bolt and ejector reversable. Simple. Done. There is no need to make it more complicated than it has to be. The best gun designs are not the more clever ones, but the most elegantly simple.

Andrew Wyatt
December 29, 2003, 02:34 PM
Other ways to look at it... Instead of a pan style mag system like a P-90 or a Lewis... why not a rotary mag like a Calico or Bizon? (just use flat nosed bullets instead of sharp points) you don't have to use flat pointed bullets. Calico made a couple models of 5.56mm assault rifles.

George Hill
December 29, 2003, 02:45 PM
I did not know that.

December 29, 2003, 03:01 PM
These are all great theories, the hard part is making them work. :)

Andrew, the only reason you would have to take the gun apart to clear a malfunction on forward eject is because it was designed that way. It isn't any weirder than side ejection, it just isn't what we are used to. But since there are only 2 designs on earth that do this, and none of us have ever seen either it is all pretty much conjecture. If the receiver is designed in a matter that the ejection port is reachable then it will be clearable.

Downward ejection with angled mag insertion, I've thought about it a lot, but I think what kills you is that during the extraction and ejection it is going to be really easy for the shell casing to bounce back into the action instead of down and out. Same reason you just don't have some sort of cover over the ejection port of an existing right ejection bullpup. I imagine that an ejector design could be made that would work, but I can't visualize exactly how.

Andrew Wyatt
December 29, 2003, 03:08 PM
I don't see what you're getting at, larry. the ejection port would be open to the air and there'd be a straight path to the ground. My idea was to have the magazine on the top of the gun. thving the magazine at an angle on the bottom would probably be better, since you'd only need one mag well.

December 29, 2003, 03:16 PM
Well, George, I'd be quite content with a side-ejecting bullpup that could be reversed for lefties. The trouble with those occurs in those few instances where it's handy to fire from the off shoulder, such as when you're laying prone behind cover, say a wall.

Other than that though...

In any case a lot of countries seem to make the bullpup work. Singapore, Australia, Austria, the UK, China, and France, to name a few.

December 29, 2003, 03:21 PM
Andrew, I'm confused, if you are talking top feed with a traditional magazine (like a BREN) then you can't have a cheek weld.

I was thinking something like this. Imagine an inverted V. This is the gun, viewed from the rear. The point of the V is the action. One leg is the magazine, the other leg is the ejection path.

If you have the magazine on the left side with downward to the right ejection your are going to have the magazine turned into your body when you take up your stance. If you rotate the V until the magazine doesn't hit you in the body then your are starting to eject more and more out the side, which is what you are trying to avoid. If you design the gun to deflect the shells downward then I'm afraid that it would be easy to bounce casings back into the action.

December 29, 2003, 03:23 PM
Correia, is there any reason, as was suggested, that a configuration couldn't be worked where the magazine would feed vertically into a well, and the ejection would be downward directly to the side of the well? I mean, surely it's not IMPOSSIBLE to design this? (Don't have the R&D resources, obviously, but still)

December 29, 2003, 03:24 PM
Make it eject downwards toward the user, and have the cases deflected by a shell deflector. Bam, it ejects forward by ejecting backwards. Kinda like an AR turned sideways.

December 29, 2003, 03:59 PM
I've been working on a design for a commercially-viable bullpup deer rifle for a while now, and this is what I've decided:

1. I thought of the inverted V configuration, but I ruled it out because the spent cases will hit your arms and burn them. Point your rifly and note where the path of the cases goes.

2. If you plan on using 20 or 30-round mags (or whatever) the mag needs to protrude from the bottom of the rifle vertically. They are heavy when full, and you can't simply add weight to the other side of the rifle to balance it because they get lighter as you empty them.

3. The only way to manufacture these cheaply enough to sell requires a design that eliminates a lot of the machining used in most guns.

Any way you slice it, it is tough proposition, even before you start talking about the trigger linkage, which must be as good as the other (cheaper) traditional rifles on the rack if you want to sell it at all.

Andrew Wyatt
December 29, 2003, 04:05 PM
Andrew, I'm confused, if you are talking top feed with a traditional magazine (like a BREN) then you can't have a cheek weld.

Imagine a bren with the magazine entering the weapon at the 10 o clock position. or the 2 o clock position.

December 29, 2003, 04:10 PM
Knife sniper, and those forward flying cases under the gun are going to go where? Picture where your hand and arm are holding the pistol grip please. :)

Night, if it is possible it needs to come from somebody a whole lot smarter than me. Try to visualize it with me. Say the mag is vertical on the left, on the right, parrallel to the mag is the ejection port. The spent casing will need to extract, be moved to the right, then shoved downward, all while not bouncing around and causing a malfunction. This would have to be a pretty well controlled action to accomplish this. If you watch a regular action it is a pretty violent and straight forward system.

I imgine that it could be done, but it would be a complex system, and great care would have to be taken to get it to work reliably. That calls for some serious $. :)

December 29, 2003, 04:12 PM
Andy, that would preclude a cheek weld, or at best make the gun so that it couldn't be used ambidextrously and thereby defeat the purpose of making it downward ejecting.

Andrew Wyatt
December 29, 2003, 04:59 PM
hence the two magazine wells. if you really feel you neeed to switch sides, just move the magazine to the other well.

Badger Arms
December 29, 2003, 05:18 PM
The Steyr ACR is already an ambidexterous bullpup. It does have bottom ejection, but uses a ringfire ignition system and a unique breaching system. I think it fires from the open bolt of necessity, but I could be wrong. Just to give you an idea of the layout, though, the magazine has to be far to the rear in order for it to work properly. One thing that annoys me with my Ithaca 37 is that casings are thrown forcefully, and I do mean FORCEFULLY against my leg and foot when I eject them. Not bad with empties, but can bruise with live rounds. I'd imagine that if ejection force were not controlled, injuries can occur with a bottom-eject semi-auto.

December 29, 2003, 05:35 PM
Now, if the ACR were to be up-calibered they might be on to something.

Dunno how a flechette round would perform compared to a regular spitzer bullet, though.

December 29, 2003, 08:11 PM
The ACR was sooo promising... :(

December 31, 2003, 02:05 PM
Anyone remember the Bushmaster ARM pistol? It handily solved the ambidextrous ejection port issue by having a rear receiver that could pivot left or right, ejecting out of a port that would be exactly opposite of the magazine well. Right handed shooters pivot the magazine well to the left, where it is braced across their arm, and the ejection port is at a 45 degree angle to the right. Left handers have it exactly opposite. The big problems involve running the gas system to the rear, figuring out where to mount the sights, and heat buildup. The ARM was intened as a PDW, so the less than ideal sights were no big issue. Modern materials and heat shielding should be able to mitigate the heat issues for the user. The Gwinn Bushmasters I've seen functioned well enough, but anyone who's seen reliability issues with the rotating reciever please post.

Building this design into a carbine would be a fairly simple feat. Add an indexable buttplate (if necessary). Extend the bbl to move the blast away from the users face and increase terminal ballistics. Add a foregrip/trigger guard ala the P90 or Tavor to facilitate a two hand hold, not to mention serve as a platform for lights, toys, etc. One could mount the front sight on the now extended BBL to improve sight radius, and incorporate apperture sights (though sight adjustments will be a trick). Trigger will still, more than likely, suck.

December 31, 2003, 04:25 PM
If I were to design a bullpup from scratch I would design it to NOT EJECT.

I would use casless ammo and have the bolt group integral to the magazine. A recoil delayed blowback setup would be excellent. No ejection port, no dirt getting in my action, no weak feed lips. Just one rugged polymer box magazine with at least 50 rounds of ammo. It would load from the top and double as a cheek piece.

Since the bolt group is removed with every mag change there would be no danger of overheating. Preferably the magazine would be a one-time use disposable package lubed and sealed at the factory. The bolt group then only have to work for a very short operational life, and could thus be made of cast alloy for low cost and lightness. As we don't have brass, further weight saving can be realized.

December 31, 2003, 05:32 PM
Gabe , how do you deal with a misfire? Change bolt and mags? What happens when dirt gets into your perfect sealed magazines (because it still will).

January 1, 2004, 12:02 AM
Gabe , how do you deal with a misfire? Change bolt and mags? What happens when dirt gets into your perfect sealed magazines (because it still will).
Obviously there would have to be an unloading port. It could be a pretty simple spring-loaded trapdoor, not unlike the M16's ejection port cover, except it would remain closed unless unloading. The caseless G11 had a similar door.

I wouldn't feel comfortable putting my face against a disposeable breech block.

January 1, 2004, 01:16 AM it to not eject.

Just to follow this thought a little...what if you left a large resevoir in the stock to catch the brass, say, 2 mag's worth, and rig it such that it popped open and dumped the brass all at once when changing mags?

My initial thought would be problems with spent brass clogging, and clearing "normal" jams would be made more difficult by the enclosed mechanism, but since we're thinking outside the box, I figured I'd throw in my .02

January 1, 2004, 02:05 AM
Gabe , how do you deal with a misfire? Change bolt and mags? What happens when dirt gets into your perfect sealed magazines (because it still will).

Destructo6 has the answer much along my line of thinking. Simple misfire can be cleared with a special port.

I have a great deal of confidence in modern container sealing technology. Besides it takes quite a bit of dirt to jam the action. With caseless ammo you also need some way to protect the powder. Historically we protected cartridges individually, so why not do it as a package? My proposal isn't technically caseless, the magazine itself *IS* the case.

Think about it, what typically goes wrong in a rifle? It's the magazine and bolt group. By taking these out there's practically nothing that can mechanically go wrong with the rifle itself. If the weapon is FUBARed due to extreme contamination of the magazine, dump the mag and pop in a new one. This must be far more preferable to doing field gunsmithing.

January 1, 2004, 02:14 AM
I wouldn't feel comfortable putting my face against a disposeable breech block.

I was thinking we can vent the gases through the unloading port in an emergency. With a disposable kit it should be designed to fail safely instead to withstand failure through over engineering. At least you won't have to worry about stress fracture on your breech block from the weapon's previous users.

January 1, 2004, 02:17 AM
Just to follow this thought a little...what if you left a large resevoir in the stock to catch the brass, say, 2 mag's worth, and rig it such that it popped open and dumped the brass all at once when changing mags?


I think your reservior would have to be very large, unless you can store the spent shells in an orderly way. Worth testing though.

January 1, 2004, 03:59 PM
Ooh...Caseless ammo. My tilt receiver suggestion is simple by comparison. The G11 didn't use caseless ammo just to come up with an ambidextrous bullpup, though that was a benefit of the design. The caseless ammo allowed them to achieve a specific design goal, the desired burst firing rate of 1800-2000rpm, by eliminating the extraction and ejection step from the firing system.
By eliminating the case, we of course can eliminate the need for aforementioned operating steps. It does indeed reduce the weight of the ammunition by eliminating the casing weight. Both noteworthy advantages.

However, eliminating the case raises some other issues which, along with the fifty round toploading magazine and expendable bolt group, compound its complexity of the proposed rifle. When you abandon the case, you are also eliminating the seal that prevents the hot firing gases from exiting the rear of the chamber. Now the bolt must obdurate the chamber against 40-60,000 psi of superheated gas with minimal leakage until the pressures have subsided enough to open the action safely.

Heat energy is another huge problem. While the heat evolved during firing is disipated by the metal parts of the bolt, barrel, and receiver, much of it is actually heating the casing which is then flung from the rifle, taking heat with it. Without these little heat sinks, that energy must now be absorbed by the system and be evacuated in the form of hot gas through an exhaust port in the rifle. Said port must now be positioned to clear left and right hand users, so its straight up or straight down. Dumping the bolt every 50 rounds isn't likely to cool the chamber and receiver very much. Accumulated heat will eventually cookoff the rounds, which was a problem that took HK quite a while to beat with the G11.

Unless you want a magazine like a Bren mag, mounted vertically upward, the cartridges will have to sit 90 degrees to the boreline and run along the top. To use a cartridge of any useful OAL, this almost necessitates the same rotary bolt arrangement seen in the G11. HK managed to solve the obduration problem and the vertical feed magazine simply by using a precision engineered (read expensive!) bolt and firing pin/chamber obdurator. The bolt must index nearly perfectly and be strong enough to survive multiple (50) firings with no leakage, yet be cheap enough to just throw away at each mag change. Lets not forget it must be light enough not to cancel the weight savings from eliminating the brass casings. And fifty rounds must fit within the length of the rifle ahead of the breach. That would be easier to achieve with a square or hexagonal cartridge cross section, so there is no wasted space in the mag. Of course, that means that the conventional linear bolt is all but impossible and the rotary design must be used.

The 4.7mmx21 caseless round selected by HK was designed to deliver compact rounds with low recoil, not for their terminal ballistics. They were intended to deliver their wounding effect from 3 rounds hitting in a dispersed pattern, so the relatively anemic round is less of an issue. If you want a .308 or similar caliber bullet at a reasonable velocity, the caseless rounds must carry more propellent. This means a larger in cross section and/or OAL, with the corresponding decrease in magazine capacity. It also means more heat evolved which must be dealt with to avoid cooking off the ammunition.

One could always argue that high volume production techniques can significantly reduce the cost of the replaceable bolt group in terms of machining and (possibly) materials. This is probably true, but it will be a tough sell to anyone but the military, and even then, as seen in the XM8 arguement, the weapon will need to provide an overwhelming improvement in performance to justify its adoption. Then there are logistical problems with replacing ammuntion, not to mention those with the ammunition production itself.

Seems like an awful lot of work and expense to make a rifle shorter. Should they find a way to solve the above problems and make it all work, you are likely to find yourself with a short, handy rifle that is awkward to load and has a lousy trigger.

January 1, 2004, 05:08 PM
You are reading too much of the G-11 into my idea.

My ideal caseless ammo would be more powerful than 5.56 NATO, yet lighter from lack of brass.

Second I do not like the G-11's magazine and would prefer a four stack box, even a helixical drum is better suited. The G-11's action is indeed too complex and precise, which is why I prefer a more traditional linear bolt group.

The G-11 had overheating problems because it doesn't use a disposable bolt group. Other than the barrel, the breech is where the heat accumulates. How will it overheat when I'm changing the bolt every 50 rounds?

As to breech leakage, it would not lead to MTBF of less than 50 rounds. One problem of caseless ammo in the dozens of rifles designed for them has been the built up of incompeletly burned material in the breech. My solution is simply to tolerate this fouling for 50+ shots, which isn't hard to do. It's trying to do so for 5,000+ that caused previous projects to fail.

The improvement to the M-16 would be potentially greater than the XM8. It would be more powerful, lighter, shorter, more reliable, require less cleaning and armoury maintenence, no time would be wasted loading and unloading magazines. I'm not saying the military would have any interest in such a radical design. But if the need is there, we have the technology to do it.

January 1, 2004, 05:51 PM
ejecting the spent cases into the stock still leaves you with the problem of not being able to get into the rifle quickly to clear a jam, etc.

Also, a traditional extractor/ejector setup sets the cases to spinning as they leave the action--if there is anything close for them to collide with the results would be unpredictable.

January 2, 2004, 04:44 AM
I used the G11 as a basis, since it is the only caseless semi-automatic rifle that could possibly be deemed "sucessful." Then I went on to show how caseless designs have problems that the G11 only barely compensated for, and that the proposed rifle, which gave few details as to functioning, magazine design, etc would only aggravate the shortcomings of the basic caseless design.
But given the new specs, I will address them individually. 4 stack box mag?Been done with the Spectre, and they were still large and heavy even with pistol rounds. Needs a large receiver. Feeding can be a nightmare too.

Helixical drum. Work so-so with pistol rounds. Rifle rounds ensure that the drum has a large diameter. More expensive than box mags. Heavier when loaded than chargers or smaller box mags. Must be wound before firing if a clockwork type, or else advanced by the firing mechanism, both which make a tupperware like-seal difficult to achieve.

Breach leakage would definitely lead to at MTBF of less than 50 rounds. Possibly a MRBF of 1. Superheated gas vents from the rear of the breach. Caseless rounds in heavy, vertically mounted magazine have no where to go to escape the rush of the gas. Said rounds ignite.

The linear bolt mechanism does work, so long as the cartridges are presented in the conventional feed position. The Fiocchi/Benelli used the same concept with the caseless 9mm AUPO round in their BM-2 submachine gun, which I'm sure everyone has heard of and lusts after. It used a long bolt with annular rings like a engine piston. The linear bolt also requires an extractor to clear a malfunction, which must work while allowing the bolt to seal effectively.

The whole idea seems to be based on the fact that a linear bolt does not require precision manufacture in order to function well for a short period of time (30 to 50 rounds). While I would bet that I could design an open bolt sub gun that would operate for 50 rounds at cyclic using a non-metallic bolt, that doesn't make it is a good idea, nor guarantee that such a design would be adaptable to closed bolt, delayed blowback arm using rifle cartridges. And the bolt would still require precision manufacture (the main cost, given non-exotic materials) in order to feed smoothly/reliably and facilitate the mechanical delay device. Even the M3 grease gun had a machined bolt (and bbl).

Heat would still be a problem. Changing the bolt will carry away some of the heat, however the barrel and chamber are not replaced with each mag change, nor will they clean themselves.

How about a operator confidence problem? You present the soldier with a rifle that upon each magazine change has a brand new shiny bolt group, lubricated to factory specs, along with a supply of ammunition, protected by an airtight seal. He also has no idea if his newly reloaded weapon will work until he pulls the trigger. Although theoretically weapons can break or malfunction at anytime, the most people feel that if the weapon has been functioning well for XXX number of rounds and is properly maintained they can be confident that it will continue to function. Now here we are hot swapping parts that must work together flawlessly with no fitting or even testing, are made cheaply enough to be disposable, and have an expected average life of exactly one magazine. I don't know about everyone else, but the first thing I do after repairing or replacing parts is to test fire the weapon to check that functioning as close to 100% as I can achieve, in addition to testing magazines and issued/selected ammo.

The technology for caseless rifles has been around for quite sometime. It still may eventually replace case based systems in the future, though we may not be around to see it. I don't see the disposable bolt winning over to many users though. We've learned to operate around the shortcomings of the cased projectile and seem unwilling to adopt new weapons that are equally problamatic.

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