They still have the issue that the bad guys are generally firing superior power rifles in the form of the 7.62 round. Part of the reason the army had to adopt heavier calibre weapons in the sharpshooter so as they can return fire at suitable distances.
Sniper rifles have always been >5.56 so it’s not a case of “had to adopt”
5.56 is a standard round for a host of reasons,
The 303 is bolt action and they generally had brass butt plates, the SLR was gas operated and had a rubber butt plate so the two would be worlds apart in recoil.
SLR’s had plastic butt plates that were interchangeable, not rubber. The main difference is in having a recoil mechanism to move against a spring. That’s why the old lmg had a lesser recoil than the SLR
Either way you don’t want to be on the receiving end