>>>I like the original .303 better, and its easier to rectify headspace issues to make a .303 work at its best than to start a whole new set of problems with a conversion.<<<
I have reloaded for 3 of these rifles and all had very nice bores. All of them gave poor case life with neck sized brass. What are the probabilities that all 3 had head space problems. Any changes I might make are just as much for the educational value as for the shooting value.
I think the .300 Savage would be almost the worst of all worlds.
The .300 Savage brass is getting hard to find and it is small at the head too.
I have no idea where anyone could find an affordable 7.62 Lee-Enfield magazine.
The Dutch were not happy with their 6.5X53R cartridge especially for their machine guns. They came up with a an 8X57R that was supposed to be an original Dutch cartridge though I have never been able to find any hard documentation of it. There are accounts of their machine guns being converted to it. The Dutch 8X57R was basically supposed to be a .303 Britishnecked up to 8mm.
>>>Many No.4 rifles I've examined had a visible gap between the breech of the barrel and the bulkhead of the receiver ring, so they were never properly screwed down tight to begin with.<<<
My rifle has a gap at the rear of the barrel face and the receiver. They are easier to make this way since my receiver would require a c'bored breech face otherwise. In addition the gas vent hold will not have much of a function if the barrel face is solid against the receiver. The gap acts as a duct for the gas to exhaust out the vent hole.