HOOF posted 04-18-99 05:23 AM            

Hi guys, I'm the guy who did most of the research and code changes for the 2.6 gunnery. I'm the guy who dug up the G1 ballistics charts, computed the ballistics coefficients from ballistics data, and even went all the way to Russia (electronically to dig up ballistics data on German guns for 2.6 (thanks arcfox for your help!)

In 2.5, a 20mm was a 20mm was a 20mm. Sure they had different rates of fire and velocities, but they more or less did the same amount of damage from gun to gun per hit. In the Real World, there is a *huge* difference between the 20mm used in WW2, much bigger than the 12.7mm and the 7.9mm classes.

First off let me go into detail on the 12.7mm class of guns (.50cal class). On the top of the heap, in my opinion, is the Browning .50cal gun, which has an excellent ballistic shape (thus doesn't slow down as bad as it's counterparts), fires a 48 gram round (about 700 grains), with a decent rate of fire and very high initial velocity. The Russian 12.7mm gun is similar in velocity and rate of fire and bullet weight. All the rest of the 12.7mm guns fire a much smaller round, ranging from 32-36 grams (this is why the Ki61 doesn't "feel" like it has quite the same punch as the P51B or FM2, despite having four .50cal guns, especially outside of 150 yards or so). On the flip side the lighter firing guns in general have superior rates of fire, so things aren't always that simple. Plus, the Russian and US .50cal gun is quite heavy compared to the German and Japanese counterparts.

20mm cannon however, vary considerably, and 2.6 models this much better than did 2.5. Weight of shell varies from 92 grams (German MG151/20) to 164 grams (ho-5). An Mk108 30mm round weighs about 330 grams if you want a comparison, and a browning .50cal round weighs 48 grams. 2.5 20mm modelled almost all the 20mm as if they had the same "punch" of the Hispano Suiza model 404 approximately, which falls in the middle of the 20mm range, having an excellent muzzle velocity, medium-sized shell (130 grams), and average rate of fire. It, along with the Ho-5, gets a ton of extra damage at point blank range from kinetic energy, due to weight of round and hitting velocity. The lighter 20mm tend to be the MG151/20, MG FF (light round, low rate of fire). Midrange is the Hispano Suiza cannon, and the Japanese Type 99 cannon (low rate of fire, but a large 142 gram shell), and on the high end is the Ho-5 20mm cannon found on the Ki84.

Now with regards to the MG151/20, there are a few things I need to say, since it's a rather popular gun in the arena, especially amongst the FW drivers. The MG 151/20 was derived from the MG151/15 which was a .60cal machinegun with an extremely high velocity. In essence it's really just a larger machine gun that fires an explosive round. The MG FF that the Germans used fired a 115 gram round (depending on whether you're talking the Mine round (HE), Armor Piercing or whatever). My research shows that the MG 151/20 fires either a 92 gram round or a 115 gram round. Rates of fire are the same, but the 92 gram round has a significantly higher velocity (2610 vs 2320fps) than the 115 gram round, but naturally is smaller and thus has less explosive damage. At point blank the difference is negligible, since the smaller round makes up the difference in Kinetic damage. However, vs fighters, the 92 gram round is probably better, because the higher velocity it is fired at means less deflection and a shorter time-to-target. The heavier round had muzzle velocities much closer to the MG FF gun, albeit with a much higher rate of fire. WB models the 92gram round for the MG151/20 for this reason. IMO the 115 gram round would be better vs bombers (larger explosive charge, thus more effect at longer ranges like when attacking buffs), but since we couldn't have both and since the 92 gram round is better overall for general arena work, we went ahead with it.

The point is that the MG 151/20 fires a round that's only twice as heavy as the Browning .50cal's round. Thus, kinetics alone, a bank of four MG 151/20s fire a similar weight of shot as does a P47's entire bank of guns. At range however, the Browning keeps it's speed up so much better than the MG 151/20 that at 200 yards a P47 probably has a heavier punch than a FW190a8, at least ignoring most of the explosive component of damage. For some reason, except for their .30cal guns, the Germans liked having flat-nosed shells with horrible aerodynamic properties (flat or cut-off-cone shaped noses suit fuzing very well). Almost all their guns had similar ballistic coefficients which surprised the heck out of me because I figured the larger calibre weapons would retain their speed better having a better mass-to-frontal-area ratio. Not so, according to the data I've dug up. The advantage is that planes with mixed weapons don't have to worry much about different trajectories for the MG 17 or the MG 131 or the MG 151/20 (another reason for using the lighter round, as the heavier round doesn't have the same muzzle velocity as the machineguns).

In general German planes will be noticably less potent than in 2.5. .50cal planes should be about the same as 2.5 (at least in the 100-300 yard range), while .30cal equipped planes will find serious firepower problems outside of 75-100 yards (.30cal rounds slow down *real* quick, and since Kinetic Energy is based on velocity squared, they tend to lose their punch *fast*).

One gun that requires special mention is the Ho-5 20mm cannon found on the Ki84. The Ho-5 was an enlarged version of the Ho-103 in design, which was a rough copy of the Browning .50cal. It is a shining example of what the Browning gun could have been had the US decided to make a 20mm version of it. Firing a very heavy shell (164 grams or so, vs 92 for the MG151/20) at a decent velocity and an excellent cyclic rate, it is quite arguably the best air-air weapon of the war. Two of these guns are almost better than an entire bank of four MG151/20s (at least from the numbers), and people flying the Ki84 should find it much more lethal in 2.6 than in 2.5 as a result. It's probably a good thing the USAAF outnumbered the Japanese 5:1 or more fighting inferior quality planes (production quality, not design), because this gun can really shred planes like the Hellcat quick

I was torn when we were working on the 20mm. On the one hand I wanted realism, and the real guns had this range of firepower. On the other hand, we had many, many players who were used to their planes inflicting certain amounts of damage, and I didn't really want to force them to have to deal with less firepower just because 2.5 had ahistorically greater firepower for the MG151/20. Ultimately I felt that modelling the guns how they really were was better in the long run, for if a player really wants to know how it was flying the "real thing" we have to be willing to make the hard choices of realism over "expectations". I know many people will disagree, wanting their FW190a8s to be able to vaporize planes at 500 yards like they used to be able to do, but in reality the real MG151/20 wasn't *that* powerful at long range. In fact the mine shells (the High Explosive rounds) self-destructed after only .3 seconds. That's barely 200-300 yards! (and is also why you'll read anecdotal stories about P47 pilots seeing puffs appearing all around them, then looking back and there is a FW blazing away at them). Since we don't (yet) differentiate between AP , HE, and other shells, we couldn't put this in (the AP rounds don't explode at all so they are good out to 1000 yards or more), but now I understand why the Germans self-destructed the rounds like this.

I hope this helps in understanding some of the detailing that went into 2.6's gunnery.