Enfield apparently made about 10,000 of the hammer-forged barrels. Of these, about 2,500 would have been used on new L42, L39 & Envoy conversions, then an unknown number sent to military store as spares for L42/39. Hundreds or thousands of barrels were released into the civilian gun trade, where they were made up into L39/Envoy clones and P14 target rifles.
The rib brazed onto the top of No4 action was a fairly common experiment at the time that the first proper single-shot closed receiver target rifles were being introduced. The rib was thought to offer some stiffening to the action. In practice, it appears to make no improvement to shooting performance, or even a slight negative effect.
https://www.milsurps.com/images/impo...90888323-1.jpg
https://www.milsurps.com/images/impo...90888321-1.jpg