Regarding the difference in performance of rifle grenades between the M1903 Springfield and the M1 Garand rifle, once again, I am likely going out on a limb here. I have only fired two rifle grenades, both from an M1 Rifle, in my life, so am not expert on them. For an accurate description of the features of the M7, M7A1, M7A2 and M7A3 Grenade launchers used with the M1 Rifle. I will only use those parts that describe a feature that may cause some differences in the range tables between the manually-operation, bolt-action M1903 rifle and the gas-operated, semi-automatic M1 rifle. The difference in the type of action on these two rifles may be the reason for the difference in information about the range of the grenades used.
The M1903 Springfield requires the launching unit to be simply a fixture for holding the grenade and for adjusting the range of the grenade, basically. The M1, being gas operated, has other “needs.” No explanation for the Springfield is needed, as it is so basic.
In the case of the M1 rifle, the grenade launchers have a built in feature, differing slight on the original M7 than that of the later modifications of the launcher. Here is a description from FM 23-30, “Grenades and Pyrotechnics,” October 1959, Chapter 3, “Rifle Grenades”: “When the launcher is attached to the rifle, the stud on the frame of the launcher rests on top of the valve in the gas cylinder lockscrew of the rifle. When a grenade is fired from the launcher, a slide and spring assembly in the launcher frame fitting against the bayonet stud allows the lanucher to move slightly to the rear. This slight independent recoil causes the stud to open the valve in the gas cylinder lockscrew momentarily, permitting gas to escape. This prevents damage to the recoiling pars of the rifle.”
This feature applies to the firing of the M3 Grenade Launching cartridge with the M7A1, A2 and A3 launchers. The M7 (original version) launcher works a little differently:
“The M7 launcher is also limited standard. It is similar to the M7A1 except that it has a longer stud and does not have a spring and slide assembly in the launcher frame. When the launcher is attached to the rifle, the stud is long enough to depress the valve in the gas cylinder lockscrew. The valve remains open all the time the launcher is attached to the rifle.” (This feature did not allow semi-auto firing of ball ammunition thru the launcher, as gas was bled out of the gas cylinder, below the barrel of an M1, leaving insufficient gas in the cylinder to allow the rifle to function in the semi-automatic mode.
This may be the difference between the firing of grenades from an M1903 rifle as opposed to from an M1 rifle. It may also take a different cartridge. That is for the .30-06 cartridge collectors to answer. It is possible that the M3 Grenade launching blank is not used with the Springfield, and that if there are earlier types of cartridges, they were not authorized for use with the M1.
I hope this explanation is clear. It sounds very complicated, but is actually not.
I will mention that I am assuming the type of operation of the two rifles is at least one of the factors in the two requiring their own separate range tables.
EDITED TO INCLUDE THE FOLLOWING:
In returning the above-referenced manual to my library, I found I also had FM 23-30, "Hand and Rifle Grenades, 14 February 1944, with some addition information. Firstly, by 1944, the Grenade Launching Cartridge Caliber .30 M3 was used with all rifles in issue. Note that I said “rifles.” Carbine Grenade cartridge, caliber .30 M6 was used with the M1, M1A1 and M1A3 Carbines, although I can’t imagine firing grenades from the second and third version of the Carbine. The launchers themselves were the Grenade Launcher M1 which was used with the various versions of the M1903 Springfield. Launcher M2 was used with the Model 1917 “Enfield” .30 Rifle. Launcher M7 was used with the M1 Rifle and Launcher M8 was used with the various versions of the M1 carbine.