The big enfield can also have it's really only weak point fixed by using a coil spring on the ejector and doing away with the leaf spring set up which is prone to breakage, usually at a bad time. To do this just cut off the leaf spring from the ejector and cut two shallow notches in it that match up with a stout coil spring. Solder the coil spring in place with a low tempriture solder and cut to length.
In many cases the rails of the action and the length has to be altered and here we must proceed with care. As I mentioned the front lower recoil lug should never be cut back further then the top lug. However the rear of the action can be cut back quite a bit. The rails should be opened up very carefully or you will have cartridges popping up on their own and a junk action. To open up the rails you need a hand full of dummy rounds and the ability to anilise things and lots of patients. The radius of the rails should for the most part match that of the cartridge. The shoulder of the cartridge should angle up as the bolt is moved forward and as the bullet rides up the feed ramp the cartridge should pop up and under the extractor. To get everything to work right you might have to polish down the feed ramp. If the cartridges are binding do not get carried away with the grinder as the problem may be with the follower. It's radius too has to match that of the cartridges. In any case the rails should be just slightly wider then the cartridge head at the rear and closely match the tapper of the round.
The cartridge must come up enough when in the magizine and the bolt fully to the rear so that the bolt hits the case head as it is moved forward. If as the bolt is moved forward and hits the cartridge the round dives down check your mag spring and the front of the rails.
This is really trial and error and you must go slowly or you will get into trouble. If you try this and need some help please feel free to call me! 207-938-3595
If this comes out it is a picture of an Enfield opened up to take the .366DGW cartridge whi based on the .416 Rigby case, it is on page 201 of the tenth edition of Cartridges of The World if you are intrested.