In his article Why Bullpups?, noted GPC proponent Tony Williams argues that a bullpup rifle is the best platform for a general purpose cartridge. I remain skeptical, for a few reasons.
1. Gun Length
A major advantage to bullpups is the shorter overall gun length for any given barrel length. This allows better handling in vehicles, in buildings, and in many urban combat situations.
However, this advantage decreases with decreasing barrel length. A 33″ M4 Carbine handles better than a 39.6″ M16. And you obtain that improved handling without any of the bullpup disadvantages. On the other hand, switching from a 33″ M4 to a 25″ Tavor CTAR offers less of an improvement in handling than switching from the M16 to the CTAR. Are the bullpup disadvantages worth it for that incremental improvement?
Add a folding collapsing stock (as found on the SCAR) to the conventional configuration, and you have a compact carry length of about 25″ — smaller than most bullpups available today. And the SCAR can be fired when folded. So a conventional AR can obtain some of the bullpup advantages with a folding stock and a shorter barrel.
So if a GPC can offer sufficient range (700 to 800 meters) from a 14″ barrel, the use of a bullpup design is less compelling. Williams’ proposed 20″ barrel on a bullpup adds at least 8 ounces to its weight as compared to a 14″ barrel. The weight increase is a big disadvantage, one that is perhaps not outweighed by the extra 200 meters of range for the longer barrel.
2. Effective Range
The effective range of a GPC is not simply a function of the muzzle velocity and bullet BC. A 100 meter target is easy to hit, even for a new shooter. Add 100 meters to that target range, and the increase in difficulty of hitting the target is minimal. But once you get beyond about 500 meters, each additional 100 meter of range adds significant difficulty. At that point, the bullet has slowed so that each 100 meters represents a significant increase in drop. And the slower bullet is also subject to greater wind drift.
The 600 to 800 meter range is probably the practical limit for consistent hits on a target, especially if wind is a significant factor. So adding 6″ of barrel length to a gun, to extend the range to 900 or 1000 meters is not useful. The bullet may still be supersonic, but the shooter cannot reliably hit the target. So, at that range, you really need a light machine gun (LMG) with a 24″ barrel (and perhaps a higher caliber).
Therefore, if we can find a GPC that is effective to 800 meters, with a 14″ barrel, the bullpup with a longer barrel is not more effective. It is just heavier than it needs to be, with a longer barrel than it needs to have.
3. Muzzle Velocity
But now the question becomes: Can we obtain sufficient muzzle velocity from a 14″ barrel to hit out to 800 meters? It is true that a longer rifle barrel gives you greater muzzle velocity, all other things being equal. But everything doesn’t have to be equal. It is possible to make changes to the design of the bullet and barrel, so that velocity is increased without changing barrel length.
The use of banded bullets minimizes the contact area between the bullet and the barrel, thereby decreasing friction and increasing velocity. Typically, bullets with a lead core are not banded, but the recent change to lead-free bullets by the U.S. military opens up this possibility. I’m not sure what the manufacturing obstacles might be, but with the high volume of rounds purchased by the military, any manufacturing problems are solvable.
Different types of barrel rifling can also affect velocity. A slower twist increases velocity as there is less resistance to the movement of the bullet down the barrel. A gain twist barrel could take advantage of this effect by starting with a slow twist and progressively increasing twist until sufficient bullet stability is achieved.
A new type of barrel rifling called multi-radial rifling (MRR) is said to offer this type of advantage to a great extent. The company behind this innovation, Sabatti, claims 12% more muzzle velocity, merely from this change in rifling. A 20″ barrel might increase velocity by as much as 250 fps as compared to a 14″ barrel (Ballistics by the Inch). But if the 12% claim holds up, a GPC capable of 715 m/s (2345 fps) out of a 14″ barrel can increase its velocity to 800 m/s (2625 fps) just by using MRR instead of conventional rifling, for an increase of 280 fps.
Not every cartridge and loading would be able to take full advantage of the above effects. But when designing a GPC, one could certainly seek to maximize this type of benefit.
4. Sound intensity in decibels is an often overlooked factor in comparing bullpup to conventional rifle configurations. If the barrel is 8 inches closer to the ear of the shooter, the increase in sound intensity is about 3.5 decibels — about twice the sound intensity, given that the decibel scale is logarithmic.
See this website: How does the sound or the noise depend on distance from the source? and scroll down to “Distance-related decrease of sound level”, which calculates the difference in decibels based on distances.
This factor can be negated, if the bullpup uses a longer barrel. For every inch of barrel length, the sound intensity increases or decreases by about one decibel. So you would need 3 or 4 inches of barrel length added to the bullpup configuration to cancel the disadvantage of sound increase. But that barrel length increase would then diminish the main advantage of the bullpup, shorter length. And it adds to one of the disadvantages of the bullpup, greater rifle weight.
If you propose a silencer on a bullpup rifle, again the rifle is longer and heavier, presenting the same disadvantages. The silencer is also closer to the shooter’s ear, and so it decreases the sound intensity less than if it were on a conventional AR.
5. Muzzle Blast
Muzzle blast will also be a problem with any bullpup rifle, as the muzzle is closer to the shooter. For a GPC designed to be effective out to 800 meters, muzzle blast becomes a significant issue. You are pushing the cartridge to its limits. And you don’t want a 20″ barrel, because of weight and handling problems. But the shorter barrel will increase muzzle blast. In which case, the conventional rifle is a better choice to minimize that effect.
6. Weight Distribution
The bullpup has its center of gravity closer to the shooter, resulting in a better balance and somewhat better handling. The M16 has its weight too far forward for optimum handling. But a conventional AR with a short barrel (M4 Carbine) mitigates this problem. Add a silencer to both types of rifles, and the advantage of the bullpup increases. There is no denying that bullpups have better weight distribution, which helps handling.
Williams’ article goes through a number of complaints leveled against bullpups in terms of weapons use: clearing jams, changing magazines, switching the rifle from one shoulder to the other, etc. Generally, the conventional layout is better in this regard. Williams minimizes the differences, but he is unable to assert that the bullpups have an overall advantage on this point.
The U.S. military trains with conventional ARs. So a switch to any bullpup would require major retraining. That is not likely to happen unless the bullpup offers a very compelling advantage in warfare. And I don’t think the benefits of the bullpup are that significant. There are certainly some disadvantages to the bullpup. And the few advantages, mainly shorter gun and better weight distribution, are either outweighed by the disadvantages, or at least not sufficient to cause the military to change weapons systems.
For the civilian shooter, a bullpup in 9mm would be a pretty good choice for home defense. It is compact enough to use inside, for house clearing drills. And it can be effective outside at up to 100 meters or so. The issues of noise and muzzle blast are minimized by the use of the 9mm round. The civilian legal (non-NFA) barrel length of 16″ works fine in a bullpup. And a silencer (where legal) can be added to the weapon without making it excessively long. And a magazine change might not be needed in most self-defense situations.