March 30, 2005
Why bullpups are a persistently bad idea
For some reason, the the bullpup rifle keeps being put forward as a good idea.I'm an engineer and a firearms expert, both by training and by inclination (if not by employment), I have a great appreciation for good engineering, and let me tell you, bullpups are poor engineering.
The bullpup rifle only has one real advantage; in that bullpup designs allow a longer barrel for a given overall length of arm.
On the other hand, the bullpup has MANY 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.
- If a bullpup has a catastrophic failure, instead of the explosion being six or 8 inches in front of your eyes, its right at your eyesocket, or touching your cheekbone or ear. The only good thing is if the bolt flys back, it doesnt end up in your eye socket. They also tend to eject hot brass, and vent hot gasses in the vicinity of your eyes and ears
- Mag changes on a bullpup are much slower because they require more repositioning, and are 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. Magazine wells should ALWAYS be either in your dominant hand, or just in front of it, because it is far more difficult to manipulate anything dextrously that is located behind your dominant hand.
- Because of the positioning of the mag, bullpups can be difficult, or impossiple 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 lowets point of the rifle, and being located behind the dominant hand, it will tend to strike the ground forcing the muzzle downward. This also causes problems with mags being warped or ripped out of the magwell, or the rifle itself being ripped out of the users hand when hitting the deck; that a conventional rifle doesnt have (the muzzle will just bounce up)
- 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 with your support hand.
- Bullpups are naturally balanced in a non-instinctive way; the balance point on most bullpups is in between your hand and your shoulder when mounted. 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 wont make a difference (and even then it will still be more awkward and less instinctive to point). This will tend to make a bullpup shift unless it is tightly mounted to your shoulder, and especially will tend to shift during rapid fire. This tendedncy is somewhat countered by the position of your support hand so far forward on the barrel, but not sufficiantly so.
-- A conventional rifle is balanced in between your dominant and support hands; and there're reasons for that. A human being natually handles things better that balance in the palm, or in front of it.
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 (they use the FN-P90 PDW which isnt exactly a bullpup, but follows the same concept), and they do jsut look kind of futuristic.
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).
Here's the thing, every study that the British did showing that the Enfield design was ergonomically correct, or that the reliability issue was solved, has over the past few years been proven to have been "Unjustifiably optomistic", or some other such euphemism for fraud.
Both the Enfield, and the FAMAS have proven to be rediculously unreliable, though at least the SA80 is quite accurate when it functions properly.
The enfield in fact is so poorly designed, that mounting it on your left shoulder will give you a black eye (and can break your cheekbone) and send hot brass and gasses flying into your eyes. You also cant fire the thing from the left side of cover without exposign your whole head and torso.
I am by just about anyones defniniton qualified to judge small arms quality; having fired weapons in anger, lugged various weapons through the field, jumped out of airplanes and helicopters with various weapons, been shot, trained people with various weapons, repaired and altered various weapons, and sold various weapons professionally.
I have tried the P90, the Enfield, the Steyr AUG, the Bushmaster M17, the FAMAS, and the IMI Tavor (the latter two held but not shot), and I haven't found any of them to be remotely comfortable, or anything but awkward. I've tried a couple of bullpup conversions from other weapons as well, same thing.
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 condtions etc... they can't know how unsuitable they are as anything other than a niche weapon, to be used only where OAL is the most critical factor, but an SMG or collapsible or folding stock are inappropriate choices.
I can't actually think of any such niche, but I'm sure one will come to me eventually....
People say "Well the designs jsut arent good enough yet, I'm sure as they mature they'll get better, isnt it the natural way to go eventually?"
Engineers aren't miracle workers. We can refine a design until it's mechanically perfect, but
the point I'm trying to make, is that there is no way to design an ergonomic bullpup, because their design is inherently un-ergonomic.
A reader suggested building a .45ACP bullpup carbine as a great weapon for tankers and support personnel.
The only real advantage of the bullpup is OAL, and the longer barrels allowed by the configuration. Given conventional .45ACP ballistics, there is little or no significant benefit to having anything more than a 16" - 18" barrel (even for .45 super).
Given a 2-3" action length behind the breech face (about the minimum depending on exact design), and an 11" length of pull (common for carbines), the minimum overall length for a conventional carbine would be something like 32".
By allowing for an action that cycles into the stock (as in an AR) you can reduce the OAL by the length of the action for a minimum length of something like 29".
The kel-tec carbine, which has a 16" barrel, and cycles into the stock, just happens to be 29" with an 11" length of pull.
For comparison, the shortest normal version of the MP5 has an 8" barrel, and is 27" long with the stock extended.
The minimum length of a semi automatic bullpup design, given the same 16" barrel, 2-3" action length, and 11" length of pull, with a 2" buffer between the back of the action and your shoulder (about the minimum, no-where near the ideal ergonomically as it would vent hot gasses into your ears and hair) is about 20-21" or thereabouts.
Please note, that at 20", the gun would be extremely unweildy, and just plain uncomfortable. Your hands would be touching each other, with the muzzle just 2" or so in front of your support hand.
For comparison, the shortest bullpup I can find is the walther G22, (in .22lr) at 28.5" with a 20" barrel. Take off the extra 4", and you've still got a 24.5" gun. You might be able to cut a couple of inches off the stock (the normal configuration includes a 1.1" butt pad, but that's not included in the 28.5" measurement), but I don't think you could cut 3.5". Also a .45acp action might be able to be as short as a .22lr, but that would take some gyration. Given that, I think my 21" number as an absolute minimum is solid.
Now, extrapolating to assault rifles, let's do another comparison:
The OAL of an AR-15 (which has an 11"-13" length of pull depending on the stock) with a 16" barrel and the stock extended is 34" (collapsed is 30.5", and the A2 stock is 3/8" longer).
The OAL of a Steyr AUG (which has a 14" length of pull), with a 16" barrel is 27" (This coincidentally is the same length as the MP5)
There is a 7" difference between the two, which is about the same as the difference between the minimum length of a conventional carbine, and the minimum length of a bullpup carbine.
They are both about 5" longer than the minimum of a .45acp of the same configuration.
The difference in nominal OAL between the two calibers is only about 1", so I wonder if we couldn't trim a few inches off of either design, even accounting for the vastly different energies involved. I would guess we could trim maybe 3" off the length of a .223 carbine or bullpup, given the absolute ideal design.
Anyway the whole point of this analysis is to show that at the minimum lengths of their designs, the difference in length between conventional and bullpup designs doesn't really produce any real difference in handiness or maneuverability.
Now, try a little experiment. Take a yard stick, and cut it off to 22", put it up to your shoulder, wrap your support hand around it with the back edge at 14", and make a fist like you were holding a pistol grip jsut behind your support hand. This will simulate a 22" long bullpup carbine with a 16" barrel as described above.
You might notice that your elbow actually sticks out further than the muzzle of a 22" shoulder mounted long gun would. In my case its about 4" more. Now move the stick around, aim, bring your eye into aiming position etc...
You might notice that for comfort, you really want something at least 27" long. It will let you move your hand out to about 13-14", and move your support hand about 2-3" forward.
Now take a tape measure out, and measure the length from your fingertip to your shoulder seam.
Guess what, for an adult american male its probably somewhere from 24-27" (mine is 30", but I'm a pretty big boy).
Importantly, for comfort and control; you arm should be bent out to no more than half that distance, and no less than than half minus the distance from the center of your fist, to your first index knuckle when it is in trigger position.
So for most people the maximum length of pull should be no longer than 13.5", and no shorter than about 9.5", a fairly broad range (note this is ergonomics not tactics, a tactical crouch requires a shorter length of pull. as does body armor and LBE).
For your personal proper length of pull, make a fistwith your index knuckle in trigger position, then tuck your arm in and bring it up to the center of your chest, and measure the distance from the center of your fist, to the inside of your elbow. Most people will be 9-10" here, I'm at 11.5 (which is the LOP of the A2 stock)
It is worse to have a longer LOP than shorter, because as your reach is extended, you become less dextrous, and begin to lose some squeeze strength and steadiness in the hands (though the difference isnt very noticible till you are several inches too far out); though if the LOP is too short you will not be able to properly hold the weapon in the mounted position, and your accuracy will also suffer.
note: there are two ways to measure length of pull, from the butt to the center of a pistol grip, or to the face of the trigger. For conventional rifles it is generally measured from the face of the trigger, but for assault rifles it is generally measured to the center of the pistol grip.
Now here's a fun little piece of ergonomic science thats a couple thousand years old, and has to do with natural balance, and body mechanics.
The shortest end of the ideal length range of a long arm for a human to wield two handed; is the length from your index finger tip to the center of your shoulder joint, which as I mentioend above is between 25-27" for most.
Note:
This is also the longest an obejct intended to be wielded with one hand should be from the center of your grip to the tip. The ideal , is the distance from the tip of your index finger, to the center of your elbow, which for most is 14-16"".The longest end of the ideal length range is the distance from the center of one elbow joint to the other (us from your elbow to the center of your chest, doubled), which for most people is from 36-40" (mine is 42)The ideal length of an item to be wielded in the fist, like a handgun, is the distance from the tip of your finger to the crease of your wrist and palm, which for most people is 6-7". The object itself should be measured from the center of the grip to the end sticking out past the fist. Funny enough a Commander length 1911 is a little over 7.5" long, and about 6" to the center of the grip. Gee... I wonder...
The "ideal" length is the distance from your index finger tip to the center of your chest. On the average adult american male it's from 32-35" (mine is 39")
So for the average adult male, for natural balance the ideal length of a shoulder arm would be somewhere between 25" and 40", with the absolute ideal falling between 32-35".
Funny enough that's about the same length range as the rifles above, and of most assault rifles and carbines of the past 60 or so years. Even funnier, the 16" AR-15 is... wait for it... 34" long, dead in that range....
Hmmm, I wonder... Interesting how that works out really.
This little measurement scheme, in somewhat less precise terms; has been used for Bows, staffs (double the measurements), and swords since we started making them.
So, bullpups are only slightly shorter than their conventional counterparts (maybe 7 or 8" in the case of an assault rifle), nothing to sneeze at, but not a huge advantage in most cases considering thte missions they are intended for; they are unreliable, they are ergonomically incorrect, and they are more likely to injure their user.
I'm not denying there are situations where a bullpup is appropriate (some .50cal and/or sniper rifle designs for example, where the primary balance point is a bipod instead of your hand, and the cupport hand will ofetn be used as a support on the stock), but I can't see any conventional situation where a bullpup assault rifle is the right tradeoff to make.
But they look cool...
Posted by cbyrne at March 30, 2005 05:20 AM | TrackBack