Originally posted by -ammo-:
This is not entirely true. Now I dont know about what WW said about the guns firing in a synchronized fashion. Sounds like he knows what he is talking about though so I will assume he is correct.
There is no synchronization per se, so much as all solenoids are operated by the same switch, being energized at the same time.
However where I do know there is error is the part where he says that all 5 projectiles from the browning's that fired at the same exact time will remain in a tight group all the way to POI. Each barrel of each individual gun has its own "personality". Every time the gun fires a wave runs through the barrel, this wave is refered to as its harmonics. Harmonics are present in all firearms, but there have been designs that reduce the "wave" or its harmonics, therefore enhancing accuracy. A notable example would be in a target rifle where the barrel has a large diameter, refered to a bull barrel. Other manufacturers mill "flutes" into exterior surface of the barrel to make it more rigid. What happens when the round is fired is this- The low order burn in the chamber propells the projectile down the barrel. at the same time the barrel harmonics has it vibrating. Where the muzzel of the barrel is in its harmonics when the projectile exits the barrel will have the greatest effect on the POI of the round. Even if you were in a vaccuum, harmanics would cause dispersion at the POI. Now take in effect the enviroment, wind, atmospheric temperature, mass produced ammo ( all ammo is NOT created equal).
Okay, let's discuss these issues you raise. First, let me give you some background so that everyone will understand where I'm coming from, so to speak.
Since 1991, I have been working with major firearms manufacturers developing sensors that are installed in many different weapons. This sensor package monitors the discharge of the weapon and does several things.
1) It records the date and time of each round fired to an accuracy of .001 seconds. This data is stored in a chip.
2) The device records the angle and azimuth of the barrel. Likewise, this data is stored.
3)Some versions are used to trigger a laser (used on the Army's new I-CIDDS system).
4) all data is later downloaded to a PC or Palm Pilot, either by cable or IR transmission.
In the process of developing systems for various weapons, I have extensively tested such weapons as the Mk.43 and M-60 machine guns. Included are the M16A2, M4A1, HK MP-5 and MP-5/10. Also tested were the SigArms 550 and 551, Browning M2HB, Barrett "Light 50", M40A1, M24, Colt ACR, M249 and the Navy's Mk.38 25mm Chain Gun. I can include many handguns as well, but will save that for another time.
When these weapons are tested, they are fitted with an array of accelerometers to monitor motion, resonance, recoil force and
other phenomena associated with discharging the weapon, both in single shot and automatic mode. Frequently, we film the testing with high-speed cameras, as well as using lasers to measure distortion under load. Indeed, there is virtually no dynamic that is not measured. For example, the data stream will reveal the response time of the primer to being struck by the firing pin. Every dynamic is viewable and every functional dynamic of the weapon can observed. In other words, we can define exactly how the weapon behaves when fired. To my knowledge, no other organization has ever attempted to collect the volume of data that we accumulate on each weapon.
Now, lets look at the "personality" of a firearm.
There is no doubt that each individual weapon manufactured has unique properties that distinguish it from others of the same lot or production run. This is due to the fact that machine tolerances are not especially tight in firearms. You can find slight differences in two barrels, broached with the same tooling. You will find slightly different bore or barrel diameters through a production run due to tooling wear, contamination and variations in alloys.
Indeed, no two firarms are identical. Nonetheless, these difference are not significant. We can add to that the simple fact that most ammunition, and to a lesser degree, match grade ammunition, have a greater variance from round to round and from lot to lot than do the weapons.
Harmonics: You would be surprised at how little variation actually exists between weapons of the same type. For a harmonic resonance to disturb the path of a bullet, the barrel must be displaced relative to its point of aim. Typically, such displacement rarely measures more that a few ten-thousandths of an inch in the extreme case. Lateral displacement is minimal because there is very little vector energy directly applied to the barrel. The energy that distorts the barrel is generally reflected energy, and to a very limited extent, barrel expansion under pressure. The effect gained by free-floating a barrel is that reflected energy is not transmitted from the fore-stock into the barrel, thereby increasing lateral displacement. Such displacement can induce a deviation in the intended path of flight, but usually limited to less than an inch at 100 yards. M2HBs do not have a fore-stock.
This does not translate into a significant deviation at 300 yards (a typical engagement distance in ACM) which could be construed to be the dispersal range that effects results.
Wind, temperature, humidity and so on, will effect all projectiles equally if fired at the same instant. Subsequent rounds may vary from the initial rounds, but there are other, more significant factors effecting them. Let's look at those factors.
Unlike most weapons, the Browning M2 operates via the energy of its recoiling barrel. The barrel moves rearward upon firing. This energy is used to unlock the bolt, which then moves rearward, dragging the empty case with it, where it strikes the ejector and flies out of the open receiver. A spring forces the bolt forward and it strips off a new round from the belt as the bolt closes and is locked in place. In terms of repeatability, the M2 is considered a very tightly locked system. Its inherent accuracy can be understood when we realize that unmodified M2HBs were used for extreme long-range sniping in Vietnam. These weapons were fitted with Unertil or Redfield telescopic sights, the same issued for use on Remington and Winchester sniper rifles. With a little practice, it is a simple process to squeeze off a single shot, while not disturbing the aim point. Kills were recorded at ranges easily exceeding 1,000 yards. Within that context, we know that a properly maintained M2 will provide superb accuracy and that harmonics are not a significant contributor to dispersal.
So what is?
That's easy to answer. The aircraft itself is the major cause of any dispersal. Moreover, we can lay much of the blame to the fact that aircraft are moving through a fluid in three axis. These aircraft will suffer motion from recoil, but generally it is uniform, and it the case of the P-38, very close to its centerline axis. Aircraft suffer from motion in pitch and yaw, and to a lesser degree, roll. Yet, the P-38 is a very stable gun platform for several reasons.
1) Having the guns as near to the centerline as possible reduces recoil induced pitch-up too. Unlike wing mounted guns, the nose mounted weapons do not induce significant yaw, especially problematic if one gun should jam in a wing mounting.
2) The P-38 is also very stable in its roll axis, far less jittery than most single-engine fighters and not subjected to torque.
3) Likewise, the Lightning has greater stability along its pitch axis, due to the long moment arm of the elevator. This is a fighter that needs very little elevator trim.
Another factor is the variation in the ammunition. Slight differences in the powder drop, bullet weight, dings and dents in the jackets, crimp pressure and several other factors conspire to vary both velocity and accuracy. Again, I must emphasize that these variations will not result in inaccuracies greater than a few inches at normal engagement ranges.
Mount rigidity: All airborne gun mounts have a degree of flex. However, any movement can be measured in thousands of an inch and is usually found along the barrel's axis. This is more a result of wear and stretching of metal. Lateral diplacement and yaw motion is minimal, simply because there exists very little energy in vector.
One last factor. Boresighting. Every fighter gets boresighted on a regular basis. Pilots have their favorite setups. The P-38 can have its guns set to converge at a theoretical point, or they can be sighted parallel, with dispersion being minimal on the sighting range. Either way, dispersal is not significant at the ranges typically encountered in WWII ACM.
Handloaders take great care to measure powder charges to help alleviate accuracy problems. Now in WW2, obviously, quantity over quality, was the word for the day. Also another thing, the vibration from all those guns, and the less than rigid mounting, and the consider the AC is not the greatest platform to faciltate inherant accuracy, and you can now see that why there was alot of dispersion, especailly at greater ranges.
Note that I have not disputed that dispersion is greater at extreme range. However, we should be confining our discussion to "effective range", distances under 1,000 ft. Moreover, in a snap-shot situation, dispersion is not an issue as only the first group of rounds is in question. Unless, the pilot trys to pull lead and let the enemy aircraft fly through the stream. In such cases, maneuvering, more than any other factor, will create a cone of dispersal, wherein the weapon, ammuntion or mounting are not of great significance. The greatest disperser of fire is the motion of the aircraft, which is never anywhere near as precise as the accuracy of the weapons themselves.
My regards,
Widewing
[ 08-29-2001: Message edited by: Widewing ]
