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Glider said:The blunt shell would actually have basically little if anything, to do with the sectional density but it would have an impact on the Free Form which is about aerodynamics.
Interestingly its the Tracer that has a large impact on the aerodynamics, as it causes an increase in pressure at the rear of the shell where there is an area of low pressure. As the shell passes through the air it creates a vacuum effect behind the shell, which in turn sucks in the air that the shell is passing through. This causes turbulence (drag) and the drag reduces efficiency. By increasing the pressure the tracer reduces the amount of turbulence and reduces the drag. As you would expect streamlining has a similar effect.
Free Form ??? There's no such thing Glider.
That would imply that the particular incendiary machine gun rounds in question (esp. .50 BMG) simply carried more of the chemical agent than the explosive machine gun rounds of the opposite side and can thus be considered more effective, which makes sense.koolkitty said:On the HE machine gun rounds, there are a few reasons behind that statement (besides the "20 mm was determined to be the smallest caliber for a shell with worthwhile explosive capacity" statment -which is obviously debatable), The MG 131 HE round carried only 3.5% filler (1.2g) and the Italian-Vickers 12.7 mm even less at 2.2% (.73g) while the .50 BMG and .50 Vickers carry ~5% as pure incendiary rounds. ("de wild" derived)
Glider, I know there are advantages with the tracer (post #101), as I posted here a while back, I also didn't mean to imply that there would be a difference between the SD of the blunt shell to the streamlined one. (just pointing out that there was a substancial SD advantage)
I also posted earlier on the cannon armmed F-86 (post #100), but it seems to have been overlooked. In addition to the cannon armmed F-86K interceptor, there were operational trials of the 4x M39 armament on F-86E's and F's in Korea as well (project Gonval).
Cannon-Armed F-86Fs
Most significantly there was the F-86H with 4x M39 armament as standard. Cannon-Armed F-86Fs
Combat range 800 m
Battery Hits/s for angle-off-tail
Type 0 deg 15 deg 30 deg
2 MK 103: 0.24 0.22 0.17
2 MK 151: 0.39 0.36 0.27
4 MK 108: 0.49 0.45 0.29Battery Fixed sight Gyro sight
Type 400 m 800 m 400 m 800 m
2 MK 103: 0.61 0.17 0.79 0.24
2 MK 151: 1.00 0.28 1.29 0.39
4 MK 108: 1.95 0.41 2.46 0.49The F86's armament was lacking, the MiG's armament was overall better. That this fact is not clearly admitted but dodged by leading the argument astray and ad absurdum is what causes confusion. Not a lack of English or reading skills.I don't believe that anyone on this thread is claiming the US was satisfied with the armament of the F86. That misconception may be caused by a failure to thoroughly read posts or unfamiliarity with the English language.
See, this is what I mean.The facts are that the F-86 was very successful against the Mig 15. Switching to 20 mm cannon was not however an unmixed blessing from a reliability point of view. One of my sources who operated the F8U mentioned that the care and feeding of it's 4-20mms was extremely complicated and not always successful.
Define poor. The MK 108's shells all had a very high sectional density, which alone should give them an acceptable BC. The 108's HE shells vary in terms of form factor, with the Ausf. C looking more streamlined than, for example, a 20x110 (HS.404) HE round. But that is debatable.My source on the various German 30 mm shells has the MK 108(mine/tracer) with a MV of 1640 fps, and calls it self destructive. I assume that means it explodes upon contact. It is very blunt nosed, not spitzer shaped which would give it a poor BC.
The point is rather to improve penetration.The MK 103(tungsten cabide core) has a MV of 3150 fps, is not self destructive but is meant for use against tanks. The projectile is spitzer shaped which would enhance BC.
Check post #114 Soren. Glider called it Form Factor there, I believe it was just a 'slip of the tounge' when he used the term Free Form.
As for the Mk108, it's trajectory was dismal, to say the last. 330 gram projectile starting out at 500 m/s, it will have dropped 40 meters at 1000 meters. Nobody in the Luftwaffe considered it a long range weapon, just a very effective short range one.
Burmese Bandit said:A note on projectile design and specifically on tracer improving trajectory effectiveness: this is seen in modern artillery shells. Modern 155 shells have a 'boat tail' to smooth airflow going around the back, combined with what to a layman would look like a slow-burning rocket at the back - the technical term is 'base bleed'. This indeed does increase pressure at the back, but it does not directly reduce turbulence - instead it pushes the area where the turbulence begins further back from the base of the shell. This reduces drag.
The effect, however, does not show much dividends at short ranges. A shell with this base bleed effect does not show much advantage over conventional shells in terms of speed retained at short distances. It is in the LONG distances that the advantages begin to manifest themselves, which is why base bleed shells have a 10-15% range advantage over other types of shells at their maximum ranges...of course, at the expense of a reduction in payload.