In this case, I'm not doing a new post, but I've completely re-written (and corrected all the typos and dead links in) the old post. In particular I greatly simplified it, pulling out a bunch of wonkish detail on human mechanics and ergonomics which just about everyone ignored.
Oh and I renamed it; since I don't actually thing they're a BAD idea, but they aren't an optimal solution:
For some reason, the the bullpup rifle keeps being put forward as a good idea.
...Really, for the most part, they are not.
I'm an engineer and a firearms expert; by training, inclination, experience, and employment. I'm a veteran, a former security contractor, a former firearms trainer, and a class III armorer and light duty gunsmith (I don't have a barrel lathe or mill at the moment, and I don't want to be an FFL again; so I don't offer full gunsmithing).
I have a great appreciation for good engineering. Bullpups are, in general, not good engineering.
The bullpup rifle has one real advantage: bullpup designs allow for a shorter overall weapon, for a given length of barrel (typically between 4" and 7" shorter than a conventional rifle).
That's not an insignificant advantage. In some missions it's even a huge asset (particularly in urban combat, or infantry dismounted from armored vehicles).
In most missions though, that 4-7 inches isn't much of a plus.
On the other hand, the bullpup configuration has a number of disadvantages:
- Bullpup designs are mechanically more complex, requiring a long trigger linkage, and control system linkages. This seriously degrades both control feel, and reliability, and increases bulk and weight (there may be engineering solutions to this problem).
If current munitions infrastructure and laws allowed for electronic trigger, feed, and ignition systems, this would be a non issue, and the bullpups advantage may outweigh it's several disadvantages; but for now, that's not an option (also, electronic systems have their own issues).
- If a bullpup has a catastrophic failure, instead of the explosion being six or eight inches in front of your eyes, it's right at your eyesocket, or touching your cheekbone or ear. The only good thing is, if the bolt flys back, it doesn't end up in your eye socket.
Most bullpups also eject hot brass, and vent hot gasses in the vicinity of your eyes and ears (some eject downward or forward, which is a better solution for a bullpup, if it's engineered properly).
- Mag changes on most bullpups are slower (sometimes much slower) because they require more repositioning, that positioning can be awkward, and can be difficult to see (if necessary) without fully dismounting the rifle.
A conventional rifle allows you to see your mag changes, and is more easily maneuvered with your dominant hand, which makes mag changes easier in general.
More importantly a human being can naturally bring their hands together in the dark. As a basic design guideline, magwells should either be in your dominant hand, or just in front of it; because it is far more difficult to manipulate anything dexterously that is located behind your dominant hand.
- Because of the positioning of the magazine (usually the part of a gun extending lowest) close to your shoulder when the weapon is mounted, bullpups can be difficult to fire while prone (though this is common with some other rifle designs as well).
Note in the pictures below, the magazine is by far the lowest point of the rifle; and being located behind the dominant hand and close to your shoulder; when you drop prone it will tend to strike the ground forcing the muzzle downward.
This can also cause problems with mags being warped, ripped out of the magwell, having the baseplate broken off, or the rifle itself being ripped out of the users hand when hitting the deck.
A conventional rifle with a long magazine can have issues with dropping prone as well, but because the mag is positioned forward of the dominant hand, instead of forcing the muzzle down, it will tend to force the muzzle up; and though it's not advisable to use the magazine as a monopod, it's possible. With a bullpup, it isn't.
This isn't an issue for rifles that are generally fired off bipods, so in an SAW or LMG role, the bullpup may be an appropriate solution (though having the feed system in such tight quarters with your shoulder and cheek is its own issue).
- Charging the rifle and manipulating the operating handle is often more difficult, and sometimes can't be done without dismounting the rifle, or reaching over the rifle with your support hand (again, some conventional rifles do share this weakness; and this is a problem that can easily be solved with proper engineering).
- Bullpups are naturally balanced in a non-instinctive way.
This is really the biggest problem, and the one that is hardest to solve with engineering.
The balance point on most bullpups is in between your hand and your shoulder when mounted, which is unnatural. We have a natural tendency to try to balance things between our hands, not between our hand and shoulder.
The only way to correct this is to put heavy things in front of your dominant hand, or to make the weapon short and light enough that this won't make a difference (and even then it will still be more awkward and less instinctive to point; but several modern bullpups have taken the second approach).
This balance will tend to make a bullpup tend to shift its butt under recoil, unless it is very tightly mounted to your shoulder; particularly during rapid fire. This tendency is somewhat countered by the position of your support hand so far forward on the barrel, by the fact that the overall leverage moment of the muzzle is lower (the muzzle isn't as far from either your shoulder, or your dominant hand), and by the fact that most bullpups have straightline recoil.
A conventional rifle is balanced in between your dominant and support hands, and there are good reasons for that. A human being naturally handles things that balance in the palm, or in front of your dominant hand, better, because we naturally want to balance things between our hands.
Under recoil, the muzzle of a conventional rifle rises, but just from gravity will fall into you support hand again without actually holding or pulling it down, because the fulcrum of the lever is in your dominant hand, and the balance point is in front of the fulcrum.
What it comes down to though, is that bullpups are ergonomically incorrect for human beings. When you have the option, you don't train someone to do something ergonomically incorrect, you redesign the equipment to fit human ergonomics.
The only good thing about a bullpup is the short overall length in relation to their barrel length; and that is not advantage enough to outweigh the disadvantages for most missions.
Well, that and the fact that they look cool, which is the real reason so many people are enamored of them.
A lot of folks have watched a lot of stargate (or played a lot of stealth shooter video games). They use the FN-P90 PDW which isn't exactly a bullpup, but follows a similar concept; and they do just look kind of futuristic.
The Steyr AUG was designed in 1976, and it still looks like a space gun:
Several countries have adopted bullpup designes as their primary service arm, notably Austria, and Australia (the AUG above), France (the FAMAS),
and the UK (the SA80 system, now in the L85-A2 variant):
The reasons cited are usually overall length, the extra accuracy and velocity afforded by the longer barrels allowed by the configuration, and some medical or efficiency studies showing that the bullpup was actually ergonomically correct.
Here's the thing: every study that the British did showing that the SA80 design was ergonomically correct, or that the reliability issue was solved, has over the past few years been proven to have been "Unjustifiably optimistic", or some other such euphemism for fraud.
The SA80 has proven to be ridiculously unreliable , though at least it is SA80 is quite accurate when it functions properly (also the HK refit and remanufacture of the A2 variant has dramatically improved reliability... Though it's still not great).
The SA80 in fact is so poorly designed, that firing it from your left shoulder will give you a black eye (and can even break your cheekbone) and send hot brass and gasses flying into your eyes. You also can't fire the thing from the left side of cover without exposing your whole head and torso.
I have tried the P90, the SA80, the Steyr AUG, the Bushmaster M17, the FAMAS, and the IMI Tavor (the latter two held and played with, but not shot), and I haven't found any of them but the P90 to be remotely comfortable, or anything but awkward. I've tried a couple of bullpup conversions from other weapons as well, same thing (excepting several bullpup sniper rifles, that I quite liked, and as I said, the P90 which is only sort of a bullpup... it's quite handy and nice to shoot).
UPDATE: Since I first wrote this, I've had a chance to shoot with the FN F/S2000 in both semi and full auto variants:
While it looks like a heavy and awkward spacegun, it's actually very light, well balanced, and comfortable. Reports from the field are that it is generally reliable, but there aren't a lot out there yet to establish a useful sample.
Mag changes are still less than ideal, and the trigger is still poor; but the handling of the gun is good, and it is reasonably accurate for an assault rifle. I do worry however about the forward ejection system. It seems to me like it would be easy to jam up in the field.
Also, since I originally wrote this, Kel-Tec has introduced their RFB forward ejecting bullpup in 7.62x51:
Unfortunately, not many of them are out in the world yet, so I haven't had a chance to fire one; but the design seems to address some of the issues above. I have real concerns about the forward and up ejection system, and the inability to clear a jam without field stripping the weapon however.
Until someone has shot thousands of rounds through them, had to change mags in the dark, and in cramped conditions, had to clear jams under combat conditions etc... they can't know how unsuitable bullpups are as anything other than a niche weapon, to be used only where OAL is the most critical factor (but where SMGs are not an appropriate choice).
For example, bullpup sniper rifles make a lot of sense, particularly in .50bmg and other anti-materiel chamberings. In fact, any weapon that you would normally fire off a bipod makes sense as a bullpup, because the ergonomic issues around balance, and lying prone don't really apply.
People say "Well the designs just aren't good enough yet, I'm sure as they mature they'll get better, isn't it the natural way to go eventually?"
First of all, why would it be?
Other than the fact that the Sci-Fi network likes featuring bullpups in their television shows, there is no reason why bullpups should be "the future". They have one design advantage, shorter length, and many design disadvantages.
Now, when we use caseless ammmo loaded in 1000 round blocks, and using electronic ignition systems... sure, bullpups make sense. At that point, all the basic engineering weaknesses are compensated for, and the advantage of a longer barrel for length of weapon offsets the balance issues... if they even exist then, given progress in materials.
But for now, so long as we are using relatively "conventional" ammunition and firing mechanisms, those engineering problems outweight the one real advantage; and the ergonomic issues simply compound the problem.
Engineers aren't miracle workers. We can refine a design until it's mechanically perfect within its design parameters; but the point I'm trying to make, is that at our current level of cartridge firing weapons development, there is no way to design an ergonomic bullpup.
So, bullpups are only slightly shorter than their conventional counterparts (maybe 7" in the case of an assault rifle), nothing to sneeze at, but not a huge advantage in most cases considering the missions they are intended for; they are less reliable and more mechanically complex than conventional designs, they are ergonomically incorrect, and they are more likely to injure their user.
I'm not denying there are missions where a bullpup is appropriate (as I said above), but I can't see any conventional situation where a bullpup assault rifle is the right tradeoff to make; even urban warfare and infantry dismounted from armor.
But they look cool...