Can some one tell me purpose of the little screw that's under the lever on circa 1900 Lefever shotguns? Thank you.

It is to lock the safety in the off position.


Glenn

That little screw adjusts the safety to be either automatic or manual--your choice.

I don't believe that screw will allow the safety to be operated manually at all, I believe it locks the safety in the off position (as Glenn noted) so that the gun is ready to fire at all times; at least that is how it works on my G Grade. In my opinion, having that screw convert the safety to operate manually would be far more preferable than the way in which it is designed; I suppose Uncle Dan was thinking this would be a great device for trap shooters, but I never seem to have a screw driver when I want to make that adjustment?

Glenn and Topgun are correct: when the top lever is brought over to its widest position to the right, the safety slide retreats to a rear 3rd position which is safety off. It will only stay there if the screw you have asked about is screwed in about one turn. The gun is now a no safety live bird gun (or in my hands a target gun). Turn the screw out and you have an automatic safety hunting gun once again.
Many of these selective Lefever safeties have been disabled or are broken, probably due to lack of understanding. My local gunsmith has been able to restore them for me on 3 Lefevers. The mechanism is well described in the reproduction Lefever catalogs available thru Cornell (http://www.cornellpubs.com/old-guns/historic-lefever-firearms.php).
Another upstate New York gun company, L.C. Smith copied this concept with their 3 way safety. Conceptually, it works the same but functionally it is dangerous because one can mistakenly pull the safety back into the fire all the time position and not realize it.

I have to agree with you,on both count's...

and that Smith safety is indeed a thing to be aware of.

For the reasons just stated I find the Lefever set-up to be preferred over the 3 position Auto/Manual as used by some other makers. Uncle Dan generally knew what he was doing.

Failure to include a proper screwdriver in your target shooting kit is not the fault of the gun but "OP".

I have a couple Flues with the 3-way as well.

As to 3-position safeties, Syracuse Arms (and perhaps other companies) also offered a 3-position safety on special request. I have only seen one example of the Syracuse gun with the 3-position safety; so it was not popular, but I agree that the confusing nature of these devices in the "heat" of shooting could be dangerous (although I admit I haven't heard of anyone being accidentally shot with a Smith gun because of safety position confusion). I personally prefer a non-automatic safety; and had the vast majority of my doubles converted to manual safety operation. Interestingly, Smith guns with the Hunter One-trigger option have a manual safety because the trigger mechanism would not permit the installation of a push bar attached to the top lever; so one will not find a Smith gun with the HOT option and a 3-position safety.

Tom, the two Syracuse L.C. Smiths I have, a 10 ga. and a 12 ga. both have the 3 position safety. I belileve in their catalog of 1888, it states that they are supplied with the 3 position safety and why.

You are correct on the FW frame, an installed HOT cannot have an automatic safety as that area where the safety slide goes is milled out along with some of the top tang to allow the second firing. It rises up and almost touches the top tang.
However on a Regular frame gun, an automatic safety can be used.
I was assured by the owner of this Specialty Gr. that this came from the factory like this.

Interesting David, I've only collected pre-13 Smiths; and all those I've owned with single triggers had manual safeties. The "R" frame on that Specialty has obviously received some special attention, as it has been lightened with extra cuts in the cocking rod channels; perhaps someone also ordered the gun be modified for an automatic safety? By the way, I haven't done autopsy's on nearly as many Smith guns as have you; but on a two-trigger Smith gun, isn't the top tang milled out on the right side to accept the safety slide bar? This example shows the slide bar on the left side of the top tang? Is this the only HOT equipped Smith gun you've seen with an automatic safety?

Tom, yes this is the only Smith I have seen with a HOT that had an automatic safety. This is the only picture I have of it and it was sent to me form the owner. If you look close to where the top lever is, you will see a pin going through the safety slide and into ______? Yes again in the position of the slot for the safety slide.

I have also enclosed a picture of a FW frame showing how the spur lever on the HOT rises for that second firing.

The goldish sheen on the side plate is from the flash.