http://www.fas.org/man/dod-101/sys/land/120.htm
From
http://denbeste.nu/cd_log_entries/20...ntheT-72.shtml
Quote "the 105mm gun for the M1 was rifled and could fire sabot rounds. However, I do think that smoothbore guns are better at it, though I'm not totally certain of why. I don't think it's because having the penetrator spinning on impact affects its ability to penetrate. My guess would be that by the nature of a rifled barrel, it presents more resistance to the projectile, so the explosive charge which can be used has to be lower and you get a lower muzzle velocity. (Use too big a charge and the gun will explode.) A smoothbore gun has less resistance and I think you can use a larger charge in the shell, resulting in a higher velocity for the penetrator. With HE or HEAT, muzzle velocity was less important (because it mainly governed the range of the gun) but with sabot rounds you need it to be as high as possible because the kinetic energy of the penetrator is proportional to the square of the velocity."
AND
"The other piece which is needed to make this work is, for lack of a better term, "avionics". (We need a term like avionics to apply to tanks.) You have to have a better targeting system. You need sophisticated electronics to aim the gun and compensate for all the things which could cause the projectile to miss, and the M1 has it. The firing system on the M1 is unbelievably sophisticated, with many different sensors and highly complex algorithms. It does things like keep count of the number of rounds fired from the gun, to calculate the effects of wear on the inside of the barrel. It has a direct sensor to measure how much the barrel is sagging. It's doing a lot of other things, too, which they won't tell us about. They can fire it while moving rapidly over broken terrain and score a direct hit on a target which is also moving, at very long range. That's non-trivial."
AND
"Update: The Clueless Brain Trust has come through again. John confirms that smoothbore guns have a higher muzzle velocity because of lower friction on the round as it passes through the barrel. (That makes sense, really; the whole point of rifling is to drag on the projectile a bit so as to convert some linear velocity into rotation.) He also says that HEAT prefers smoothbore guns, which surprised me."
Next page:
http://denbeste.nu/cd_log_entries/20...chnology.shtml
Some very interesting reading.
BTW, I didnt mean to get sidetracked.
I want one too, but I will bet they will want more than $20,000 for one!
Vern
It's a smoothbore!!! 
Linear Mode
