Friend of mine has a No1 Mk3 that keyholes factory ammo, but shoots the Hornady .312 just fine with 42 gr of 4320.
Two things in play here: it is slightly larger diameter, and much shorter because it is a round nose.
Ted
They are no longer available from Speer. I shot many, many, hundreds of them in Lee Enfields over the years. They were accurate and performed well on game.
Ted
"...Solid coppers would be best..." You'll have to make 'em. Barnes doesn't make one.
Assuming y
Thanks Ted. I'll keep my fingers crossedthat someone may have some they are willing to part with.
Johnn,
I don't have any of the Speers left, but will put a handful of .312 Hornadys in the mail for you to try if you like.
Ted