IvW,
I suggest that you buy that sidelock rifle.
If not, you will kick yourself when it’s gone.
And, despite the unwanted cartridge, that rifle is worth a lot more than the asking price of $10,000.US (a lot more).
I would bet that, you can eventually have it re-chambered and proper ejector faces installed to fit at least the .450 NE 3.25” flanged cartridge.
From everything I’ve read on the topic, the converting of .458 Winchester doubles, to .450 NE Flanged, is a somewhat common thing, among the few truly expert double rifle Gunsmiths of the world.
If I’m not mistaken, JJ Perodeau Gunmaker Inc. (Oklahoma, USA) and Heym of Germany are two very professional outfits offering this conversion.
Also, if the planets all line up just right for you, there might be enough frame width and chamber thickness to safely convert it to the .450 No2 NE.
Rim vs Rimless;
I do agree with you regarding double rifles with rimmed cartridges for PH’s and other people who choose to rely on a double, while walking among the world’s various species of 4 legged dangerous animals.
IMO, rimmed cartridges do add a little extra “sureness”, at least in the peace of mind category.
However, for the unwashed masses (myself included), well made doubles in rimless calibers seem to function well enough.
Underline the words, well made.
I mentioned in an earlier post, within this same thread that, my only double gun malfunction, ever, was with a rimmed cartridge (typical 2 & 3/4” chambered 12 bore JP Sauer Pre-War shotgun).
One barrel’s ejector would stick shut every time a cartridge was fired in that barrel.
Neither would it even extract.
A stout cleaning rod was required to punch out each stuck cartridge.
I suspect this problem was not due to standard shot shells being rimmed vs rimless.
I am reasonably sure it was due to well worn moving parts.
I sold it to a Gunsmith as is, for close enough to what I had paid for it.
Anyway, I also am with you on your fondness of the .450 No2 NE cartridge.
When firing the one I formerly owned, if you opened it with the muzzles pointed approximately upwards, the empties would always fall out.
I loved that rifle but, had racked up a $20,000. US Dollar safari bill, by shooting critters with it.
Therefore, I sold it to help pay my debt.
It was marked “Army & Navy Cooperative Society, London”.
It might also have had in addition, the words “and Calcutta” .
But my memory is foggy on that by now.
Anyway, it had 28” barrels, with square cornered riflings, bright shiny bores and chambers.
Whomever the owners were over its 100+ year old lifetime, they obviously knew their way around a cleaning rod, bore swabs, nitro solvents and preservative oils / grease.
I too babied this rifle.
Sadly, it had to go but happily, I made a profit on it when it sold.
Good old Cal Pappas helped me decide to buy this rifle to begin with and also helped very much with hand load development.
Before Cal passed away, he told me that a man he knew in Australia had eventually ended up with my rifle.
Blah blah blah whatever.
I’d like to see Heym offer their Model 89 in .450 No2 NE as a standard chambering plus, some good quality company offer proper brass for it, as also a standard product.
(But, I’d sure LOVE to see Heym and others, offer appropriate frame sized, SxS doubles in .303 British, for less than the cost of a new house).
I always enjoy your posts.
Good luck with your decision.
Best Regards,
Velo Dog.