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It wasn't but three or maybe four weeks ago the .311 Imperial Magnum topic came up in one of these two sub forums I linked.
A quick search might find what you are looking for or maybe posting your question in either of the two sub forums.
There has been from time to time some ammo offered for sale in the EE and again more general discussion , but I have not seen this discussed in the reloading section.
I'm sure the two or three guys who have one or more of these rifles can and will chime in .
Maybe the gunsmithing sub forum for opinions on the parts you mention ?