If a weaopn is designated as a thirty ot six, what does the ot six mean? I know the thirty is the caliber of the round.

thirty-ought-six. the . 30 caliber round was invented in 1906 and needed to be distinguished from other .30cal rounds, hence the '06 added to it.

Calibers have been named for many things. The 30/06 was adopted by the U. S. Government as the official military rifle cartridge in 1906...hence the "06" added to the caliber designation. There is a .22 LR, which stands for Long Rifle. There is a 250/3000 Savage...which was so designated because it was the one of the first commercial cartridges to fire a bullet at 3000 feet per second. There is the .22 Hornet, because it was supposed to be vicious and fast. Then came the .218 Bee...same theory. The .22/250 was the .250/3000 case necked down to accept a .22 caliber bullet, hence the 22/250 designation. There is a .257 Roberts developed by a Mr. Ned Roberts and of course the .220 Swift, one of the few cartridges to fire a .22 caliber bullet over 4000 fps. The study of calibers can be fascinating.

It means that the weapon is chambered for .30-'06 Springfield type ammunition. (Some European armourers refer to this cartridge as 7.62 x 63mm)

Further reading:

http://en.wikipedia.org/wiki/.30-06_Springfield

The thirty-ought-six is a very powerful rifle round that is good for hunting or sniping.

06 is the year that particular type of .30 caliber round was produced like an 02 Toyota.