Ah Ha. Dawn breaks in the West. Another superlative way to market unnecessary after-market add ons. In those halcyon days of yore, spring technology was ....... abysmal. To circumvent failure ... Make em HEAVY. It worked. Also, "In The Beginning" (stolen famous book line) toggle link rifles were not chambered in heavy brass straight walled pistol calibers. Original Henry, 44 Henry Flat, was a soft coper case that sealed the chamber nicely. Rifle shot very clean.
Enter the '73. Never chambered for a heavy brass straight walled pistol caliber. 44-40, 38-40, 32-20 were about it. As we all know, they run clean. No need for Positive Slam Down. Chambering in 45 Colt and CAS changed all that. Without a bunch of attention, the 45 Colt runs Dirty. 44 Special runs dirty, 38 Spl runs a little dirty. So, the Carrier block gets sticky.
In a stock Uberti, or original Winchester, The Carrier Side Spring powers the Carrier Block down. With a clean carrier, this is no problem but a mite stouter spring helps. With a gummy carrier, one can be in trouble. The spring will leave the Carrier Block half way up and jam the rifle solid. So, us meddling gunplumbers incorporate Positive Slam Down. The lever stays in contact with the Carrier Arm ALL THE WAY DOWN. In a rifle, well set up for CAS, the only purpose the Carrier Block Spring serves is to hold the carrier UP while the Breach Block strips the cartridge.
All the manufacturers of Short Stroke kits recognized this and incorporated Positive Slam Down in the design of their kits. For those not enamored of Short Stroke, the rifle still receives great benefit from a good action job. A good action job will incorporate Positive Slam Down. AND ..... just to be contrary, Horse Pucky. Contrary to others, without Positive Slam Down, a light carrier will jam easier than an OEM carrier.