Nemesys: Are you referring to the .223 / 5.56 issue of shooting tracer ammo (long throated chambers in AR's) ?
If you are worried about shooting tracer, don't sweat it. I've shot tracer 7.62mm ammo (surplus, gun show sourced) out of my M1A. Not a problem.
I've never had any problems shooting Remington, Federal, Winchester factory hunting ammo out of my USGI (real) M14's back in the mid-80's and then turning around and shooting some IVI ball ammo.
All you newbie M14 addicts: Shoot your rifles and mail me 5 fired cases in a 29 cent padded envelope. I will micrometer / measure your chamber's headspace for your own peace of mind or referrence.
Cheers,
Barney