OK. Let us try NOT to forget nor ignore. Winchester's 1875 Catalogue was describing an entirely DIFFERENT breed of Kat. Winchester's 1873 and 1876 did NOT have a Firing Pin Return Spring. There was also no Firing Pin Extension Rod. The Firing Pin was one piece, all the way through and was retracted mechanically. Making the action lighter was "relative." Springs in original 1866s and 1873s were much thicker and much stiffer. The Main Spring had a Strain Screw as I mentioned, the spring was retained within a dedicated Lug. Leaving some play in Winchesters original lever side springs I can understand as ALL those springs were much more prone to taking a "Set" than modern manufacture spring. Difference in metallurgy (Big Difference).
We come to Uberti. Main Spring retained by an entirely different method. A Screw. If you back out the screw allowing the spring to move around, your going to cause some really odd wear to the screw and your adjustment may also wander as the screw moves from vibration. Understand, I NEVER did an action job that included backing out the screw. If one were to do that, I would seriously council a nice dollp of BLUE LocTite on the threads.
Uberti lever side springs are ....... KRAP. Too heavy and they DO NOT fit the rifle as they should. Because they are incorrectly shaped at the back end of the spring, they DO NOT fit the contour of the frame. This is true of ALL Uberti Toggle Link Rifles. the lever side springs need to come out, the back of the spring re-shaped to fit the frame and re-installed to check the tension. Backing out the screws will allow the side springs to move around and cause odd wear on the lever cam and on the "hook" portion of the spring that rides the Carrier Block Arm and Lever Cam. Bad Juju.
If your not conversant with Spring Grinding 101, leave the springs alone and swap them out for after-market springs. After-market side springs run about 50-60 Bucks. I don't know the current tariff for Main Springs from "The Smith Shop" nor Slickmagic. All up for springs isn't going to run much over a hundred bucks.
Biggest bang for your bucks in ANY CAS rifle is a good action job. Short Stroke optional. Most folks would be amazed just how fast a '92 or '73 can run with noting more than a good action job. It doesn't have to cost a fortune and swapping out springs is easy peasy.
Almost forgot, the reason the screws for the lever side springs are so hard to get out, is because the lever springs don't align in the bottom of the frame and the screws go in cock-eyed and bind up.
Almost forgot forgot, that pesky Firing Pin Return Spring only needs to move the Extension Rod to the back of its travel. Any more spring than that is unnecessary and can cause fail to fire.
Remember, the ONLY similarities between the ORIGINAL Winchester riles and Uberti are the Toggle Links. Also, Miroku copied Uberti. NOT Winchester. Nanny Nanny Poo Poo