Hello GregP,
Perhaps I didn't explain the concept of Point Blank Range very well, but I believe you are not using the term correctly. The problem is that there is common usage and the technically correct meaning.
PBR does take into account the maximum height of the bullet's trajectory:
PBR is the maximum range at which a shooter can aim directly at his target without adjusting the elevation.
PBR is a function of the gun / ammunition and the target size.
Take for an example a common .30-06 rifle.
If my target is a basketball, my bullet cannot rise or fall more than about 5 inches or so if I aim at the center. To get the maximum PBR, I adjust the zero on the rifle so that the maximum height of the bullet is never more than 5 inches. At some point, the drop of the bullet will be 5 inches from my line of sight. THAT will be at the maximum PBR. As a guess, I would figure that to be around 250 yards or so.
If my target is a person, the US army figured out with the M1903 rifle that the maximum PBR was 550 yards (probably with around a 300-something yard zero). The bullet would not go higher than the target's head or drop below the target's feet within 550 yards.
Aeroplanes are much bigger than people, so I am assuming the distance to be considerably more than 550 yards. I didn't try to figure out how far, but my GUESS was around 750 yards or so. Perhaps I guessed wrong?
Actually barrel length, chamber length, gas port locations and internal ballistics considerations are pretty much irrelevant. All that is important is the Muzzle Velocity and the flight characteristics typically represented by a Ballistic Coefficient and ballistic model. Most people use the G1 model which is based on a 1 inch diameter projectile that looks pretty much like we expect a "bullet" to look. This was the Krupp standard bullet. That is why you get things like ballistics coefficients that change with velocity range: because the modern rifle bullet really doesn't follow that kind of flight path. Interestingly enough, a typical aircraft cannon shell DOES bear a pretty good resemblance to a Krupp standard bullet. The modern boat tailed spitzer bullet is better represented by the G7 model.
You are assigning a tactical reason to the armament configuration of the A6M. I have no knowledge of why this was done. I do know that the FW 190 series had guns selectable as well and there were less ballistics differences between the cannon and MG. (This ballistics similarity is the point I have been arguing all along.) I have always thought that the gun selection and trigger on the A6M was much less than optimal. The throttle is just not the right place to put the trigger IMO.
Regards.
- Ivan.
Perhaps I didn't explain the concept of Point Blank Range very well, but I believe you are not using the term correctly. The problem is that there is common usage and the technically correct meaning.
PBR does take into account the maximum height of the bullet's trajectory:
PBR is the maximum range at which a shooter can aim directly at his target without adjusting the elevation.
PBR is a function of the gun / ammunition and the target size.
Take for an example a common .30-06 rifle.
If my target is a basketball, my bullet cannot rise or fall more than about 5 inches or so if I aim at the center. To get the maximum PBR, I adjust the zero on the rifle so that the maximum height of the bullet is never more than 5 inches. At some point, the drop of the bullet will be 5 inches from my line of sight. THAT will be at the maximum PBR. As a guess, I would figure that to be around 250 yards or so.
If my target is a person, the US army figured out with the M1903 rifle that the maximum PBR was 550 yards (probably with around a 300-something yard zero). The bullet would not go higher than the target's head or drop below the target's feet within 550 yards.
Aeroplanes are much bigger than people, so I am assuming the distance to be considerably more than 550 yards. I didn't try to figure out how far, but my GUESS was around 750 yards or so. Perhaps I guessed wrong?
Actually barrel length, chamber length, gas port locations and internal ballistics considerations are pretty much irrelevant. All that is important is the Muzzle Velocity and the flight characteristics typically represented by a Ballistic Coefficient and ballistic model. Most people use the G1 model which is based on a 1 inch diameter projectile that looks pretty much like we expect a "bullet" to look. This was the Krupp standard bullet. That is why you get things like ballistics coefficients that change with velocity range: because the modern rifle bullet really doesn't follow that kind of flight path. Interestingly enough, a typical aircraft cannon shell DOES bear a pretty good resemblance to a Krupp standard bullet. The modern boat tailed spitzer bullet is better represented by the G7 model.
You are assigning a tactical reason to the armament configuration of the A6M. I have no knowledge of why this was done. I do know that the FW 190 series had guns selectable as well and there were less ballistics differences between the cannon and MG. (This ballistics similarity is the point I have been arguing all along.) I have always thought that the gun selection and trigger on the A6M was much less than optimal. The throttle is just not the right place to put the trigger IMO.
Regards.
- Ivan.