I purchased a couple 'Eley .577 London' cartridges at a gun show. The case length is 2 3/4". The vendor pulled the bullet from another cartridge and showed me it was loaded with black powder. He gave me this one and I weighed the powder and paper patched lead pullet. The coarse black powder weighs 142 gr and the paper patched bullet weighs 596 gr. I assume these are
577 bpe 2 3/4" rounds. Has anybody shot these in their rifles? Anybody know when these were made? I bought with the idea of shooting them. The seller has more but I want to test these before buying any more.

Yep, 5 Dram .577 BPE 2-3/4” loads. A relatively “light” load as 160 grains (6 Drams) was more common.
Those cartridges are old.....at least 100 years old (likely well before WWI) as Eley brand ceased cenerfire rifle cartridge manufacture in the early 1920’s.

They would have corrosive primers and possibly mercuric formula as well, firing mercury primers will weaken the brass for future use. This is if the old primers even function any more.

I have read historical accounts that Eley Express cartridges were said to be more prone to splitting and head separations on firing compared to Kynoch and other makes.

If they actually fire and don’t split, then reloading them will be a problem because there is no current source of the Express size Berdan primers in the USA.

All in all get new brass.......those Eley’s are best left to collectors.

- Mike