The SLR was originally intended to fire the 'true' intermediate .280 British (7 mm) round and it (as well as the EM2 rifle) was far more controllable in full auto than it was firing the more powerful 7.62x51 NATO round
The larger 7.62x51 NATO round overpowered the design and the British deleted the Automatic functionality of the weapon (although it was retained for the 'Metric' FAL rifle)
A relative of mine was on the original test group for the early SLR in the early 50s (he was a career soldier in the 'Skins') and said that Full auto was pointless as only the first round would be on target the rest increasingly above it such was the recoil.
That and the original wooden furniture would fall off
But an Assault rifle it was not