i want to know what the difference 5.56 mags to 6.8spc mags? do they have different followers and springs?they all fit in a AR lower so they cant be much of difference and why cant you use Pmags?i might be beating a dead horse or just a idiot but i still want to know

The biggest issue is the diameter of the round sis different, the 6.8 is larger.
The difference between the mags is the feed lips have been adjusted to accommodate the larger round.
There is also some internal differences in the stamping so the 6.8 rounds sit properly in the magazine.

I have read about people successfully using 5.56 mags to feed 6.8 but I'm not sure if I'd trust it.

If you look at them side by side, the ribs on the sides of the magazine (USGI Style) are more shallow on the 6.8 to accommodate the fatter round.
The internal dimension of the magazine is therefore larger.
The external dimension is the same.
If you made a PMAG like this the wall thickness of the polymer would be too thin.

The followers and feedlips are different between the two, which is why you just cant put 6.8 rounds in a 5.56 magazine.

The PRI waffle mags are great 6.8 magazines.

Can you alter a 5.56 mag to shoot 6.8 ?