Will firing the 170 Grs. Federal Sporting Ammo harm the OP rods on my M1? I have fired the Ammo in the past with out problems.
It all depends on the gas port pressure that the ammunition produces. You have to call Federal to find out.
GI ammunition had to meet velocity, breech pressure, and gas port pressures. (And other criteria)
Mind you, your rifle was put into service in 1936 with ammunition that is considered mild by today's standards.
Your Garand gas system is not self compensating. You put ammunition in it that is too high of a port pressure the mechanism will open faster/sooner than for what it was designed. Rapid acceleration will bend the operating rod. Rapid acceleration of the mechanism will slam/bang things around, cause misfeeds, op rod dismounts, all sorts of fun. And beat up your mechanism.
The heaviest bullet weight used by the military was 174 FMJBT. Pressures were NTE 50,000 cup, velocity was 2650 fps at 78 fps. Port pressure, I forget. So pressures were in the 40 Kpsia. Most modern ammunition is exceeds this and will produce higher port pressure.
The NRA had an article, decades ago, where a guy developed heavy bullet loads in the Garand. The weights were at least up to 190 grains. And the loads were slow. To keep port pressures down.
Hornaday makes 30-06 compatible ammunition.
http://www.hornady.com/story.php?s=775 That is the only commerical ammunition that I am aware won't beat up your rifle.
I load my own. My load is a 168 SMK/Hornady match/Nosler Match 47.0 grs IMR 4895 LC CCI #34 OAL NTE 3.30" I have shot 150 SMK 47.5 grs IMR 4895 LC CCI#34. Cutting either load to 46 grs won't hurt a thing.