Why is there a difference in AR-15 & bolt action load charts?

[brown3345]

I was just thinking of reloading a few hundered rounds of .223/5.56 tonight so I opened up the Sierra reloading manual and saw that there are 2 different charts for this caliber. Taking a closer look at the charts they have heavier loads for the Bolt Guns and lighter loads for the AR platform.

Now this really blows my mind because I thought that the AR Weapons are made to handle hot military loads!

Here is an example for max loads:

Bolt Gun;
55gr FMJ Powder H335 @ 27.5 grains 3,300 FPS

AR-15;
55gr FMJ Powder H335 @ 25.7 grains 3,000 FPS

What am I missing here guys?