Looking at the above photos I see similarity to Needhams side lever and a gun that looks like a Scott ,but never seen a side lever version .This could be that actions were bought from one maker and finished by another.
There were numerous patents , provisional and full , improved patents , people claiming patents and those marking actions as patent even if it was not their patent . Add in that there were many short loved actions and those that copied patented actions , where the patent had expired or never taken beyond a provisional . It is fact that many patents granted at this time would not really have stood up to a court case as they were merely slight modifications of others .
As to the advantages or disadvantages the fact that they went out of use almost entirely says something for there popularity .
That said if you have missing or damaged thumb a side lever can be the answer to your problems it can be used with the heel of the hand as can be for a left handed person who finds a conventional top lever difficult.
Reilly didnt make any of those guns or those actions Argo pictured. Two of them are 100% W&C Scotts and one is JD Dougall lockfast, an action Dougalls patented, produced and sold to the trade along with complete guns.
The Scott hammerless is built on the Scott-Baker parent and was only produced by Scott. The hammer Scott is a basic Scott trade action, used by many gunmakers and retailers.
