That's actually an inaccurate explanation/argument as it refers to the calibre of the ammunition. It's simple physics, the greater the calibre, in the case of the SLR 7.62mm, the greater the velocity required to project it and consequently the more damage it will cause. However, correct employment and usage of smaller calibre ammunition, whether it be 5.56mm or 9mm can have the same effect. Also the SLR was simply another rifle in the ongoing development of weapons. It like it's predecessors were developed for long range warfare, i.e. defensive/trench warfare, but as modern conflicts dictated more close quarter fighting the larger calibre longer range rifles proved to be too heavy and and ineffective in this type of warfare, hence smaller calibre, shorter, lighter and more effective assault rifles were needed, thus the SA80 was one of them, and was very effective.
Thank you. A certain know-it-all I know will get a lesson next time he spouts off about the subject : o )