I dont reload so bare with me.
Does a 308,7-08 260, and .243 use the same amount of powder ?

Generally, in the ballpark, yes. Meanign for all you are going to use about 35-46gr of powder. But all ultilize the powder differently. For example, a 7mm08 can ultilize IMR4350 with 140gr bullet very well, but not suitable for 308. 4064 is about the best all around for the calibers mentioned.

so how do the heavier bullets fly damn near as fast as the lighter ones.

And why does the 308 kick harder than say the 243. I mean theyre using the same amount of powder right ?

Cause of pressure. Remember you fluid dynamics and physics. Bigger hose, same pressure. Bigger bullet larger hole same pressure, same velocity.

The 308 kicks harder usually because bullet is heavier generally. The load and the bullet makes up the total mass coming out of the barrel. Bigger mass out of barrel going just as fast as 243, makes bigger boom boom. Bigger boom, makes larger recoil. Opposite effect on your shoulder as out the barrel over larger surface area (stock pad)

If you fired a 100 grain bullet from the 243, the 260, the 7mm-08 and the 308, the recoil difference would be slight indeed. Like BC said though the 260, 7mm-08 and 308, as a rule are firing heavier bullets.