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Old 11-02-2016, 10:16 AM
Corry El Corry El is offline
Join Date: Jan 2013
Posts: 2,611
Originally Posted by Gray Ghost View Post
I haven't read of sabot ammunition available for the 20mm x 102 rounds the U.S. M61 rotary cannon uses. Which strikes me as strange, given sabot AP ammunition exists for smaller cartridges like 12.7 and 7.62 mm. I wonder if it's because 20mm is primarily an aircraft or anti/aircraft weapon for the U.S., and sabots are either unneeded to damage aircraft, or pose a FOD hazard when shot from aircraft?
20mmx102 APDS rounds exist; they are the standard ammo for the 20mm Gatling gun as used in the Phalanx shipboard terminal missile defense system. They aren't used in a/c guns for the reason you stated. In a few freak cases modern fighters have managed to fly into the path of their own 20mm projectiles, not to mention a cloud of sabot petals rapidly decelerating in the a/c's path.

Anyway even with a stationary gun against a stationary target, there is enough dispersion in the trajectory from round to round to make it unlikely to hit 'the exact same spot' (say we define that as a difference of some small % of the round's diameter). And Gatling guns have a larger dispersion when the barrel is moving perpendicularly to the axis of fire at a varying speed as the gun spools up at the beginning of a burst (eventually it's constant and can be corrected for by the same degree on each shot). Some dispersion is fine; the optimum dispersion is generally greater than zero in multiple rounds against a moving target, but hitting right on top of a previous hit is not likely.

In some actual cases though antitank rounds defeated armor they were theoretically incapable of penetrating by nearby hits causing the armor to shatter. You can find pictures of armor of German tanks in WWII defeated that way by theoretically overmatched Allied antitank rounds. Of course it also might have meant the armor wasn't produced correctly. And it's not directly relevant to modern tanks where protected by heterogeneous armor arrays rather than steel plates.

The highest penetration performance quoted for any 20mm rounds are for 20x139 APDS types as fired by the Rheinmetall Rh202 on for example the German Marder Infantry Fighting Vehicle. That's 60mm per the Wiki page, 44mm at 1000m by other sources.

The lowest value I could find for M1 armor is from a Russian site's diagram showing only 30mm of steel on the lower hull side behind/beneath the skirts, and also meaning the round has to thread its way through the closely spaced road wheels. And it's just somebody's official looking diagram of classified info.
This Steel Beasts game specification shows a very narrow zone of 50mm protection just below the side skirts

But in both regards, penetration and protection, there's now a parallel world of values programmed into games which the game programmers *try* to verify in the real world, but they must come up with some detailed specification either way. The game values are often the product of discussion among people who know what they are talking about, in general technically, but who aren't divulging classified info. It's not necessarily crudely made up stuff by people with no idea what they are talking about. Many such learned discussions occurred over the years here for example, though this forum is not what it used to be:
(somehow the site also now generates an unsafe site warning. I've never had a problem, but I'm not telling anyone to proceed to it if not comfortable doing so)
Anyway, these numbers are people's estimates, possibly in some cases actual info which has leaked, but I'm not saying it's the absolute fact, and I'd recommend against people who know it's not correct from their own knowledge of classified info speaking up and saying so, even just to say that.

Practically speaking 20mm guns have negligible capability v modern well protected tanks. US claims against Iraqi tanks in 1991 even with 25mm in side shots is not to my knowledge solidly documented. There's a surprising lack of detailed public info on actual weapons effects and causes of Iraqi tank losses after all this time, besides certain well known photos which speak for themselves.