No. If you have any XM855 I will dispose of it for you... Yes you can shoot it no problems.
The answer you are looking for is Yes, you can shoot all that in your gun.
Any commercial or military 5.56 ammo or .223 will work just fine.
The 'x' identifies it as not fit for duty ammo, basically its the military's version of range ammo. It is not different that then m855 except they used to use spent brass to make it.
Sorce: took an ammo course in the Army to burn a week durring safety stand down.
According to Federal, the X designation means it was produced for the commercial market. It is produced from new components, not spent brass or rejects as many like to say. Source: Federal Ammunition and the cases of it sitting on my shelf with brand new bullets in brand new LC brass. I heard a bunch of hogwash when I was in the Army, too.