If your barrel is showing some wear might I suggest you try some Hornady .312dia bullets. their 174gr heads help greatly with accuracy. They work very well in a worn .303 barrel as opposed to the original .311dia bullets. They made a huge difference in my 2 groove barrel No4 rifle. I will also suggest using flat base bullets exclusively as that's the basis of the MK VII round. They provide greater stability as there is more bearing surface than a boat tail bullet has. 2 of my pet loads for the .303 are 46gr of IMR 4350 and 40.4gr of IMR 4064 behind the 174gr heads. Both of which provide identical ballistics to the MK VII round giving 2400fps from a 24" barrel. I have tried making the rounds hotter but that has actually reduced accuracy. The .303 in my experience is a very load specific round and doesn't respond well to tinkering like a 30-06 does.

As a side note these .312 bullets are actually for the 7.7mm Japaneseicon round so the cannelure rarely lines up with the case neck on the .303 as the cartridge overall lengths are different. I use a Lee factory crimp die on them which makes up for it.

Another thing I have noticed is the brass comes out of the P14 looking like it was full length resized compared to how beat up it gets out of the Lee Enfield actions I have. - Bill