Ya. How about 40 years for me. Just looking for something that can take the 5.56 pressures. I have been shooting 5.56 in my 223 for years and never knew that there might be an issue. Bought the cheapest ammo — sometimes 223 and sometimes 5.56.
Not likely an issue unless you shoot reloads without trimming your cases back.
Most of the chamber difference is in the "leade" (taper from chamber to rifled bore). This guy sells a 5.56 chamber reamer that cuts the leade area only and won't harm the chamber shoulder area or damage the rifle's headspace. Should be just the ticket.
Of course, if you've been shooting 5.56 ammo in it all along and never experienced any overpressure problems (see link), then your chamber may be fine as-is.