I have been offered a .577" made by the London Arms Company. A bit of research has revealed that they are well made. (Parts made to a .003" tolerance). I see they were only in business from 1855 to 1866 so any gun made by them is a rarity.

The prices seem to vary between £800 and £2,000 and from the description there appears to be little between them regarding condition.
Obviously it would be prudent to give any prospective purchase a good inspection before parting with ones money.

The one I have been offered is priced at £1,000, and belongs to someone I am acquainted with. It is allegedly in good condition. It is too far away to go and have a look (approx 130 miles). and the lockdown would prevent it at the present time.

Any comments would be of interest.

ps. It has not been converted to a Snider.