Original Winchester test results at factory on weakened toggle-link .45-75 Model 1876 tests have been cited many times. For those who haven't seen them here is an extract from Oliver Winchesters letter to Hallock.
"The strength of the Model 1876 rifle and the .45-75 W.C.F. cartridge was tested by Winchester in the late 1870s. The factory conducted tests on the strength and reliability of the action to answer concerns by customers. These tests will astound collectors and shooters who have stated the Model 1876's toggle link action is "weak." In response to a letter sent to the company by Charles Hallock, Esquire, of Forest & Stream magazine, Oliver Winchester responded by telling about the tests the factory accomplished on the 1876 rifle. He indicated that engineers first started the tests by removing one of the toggle links and fired 20 rounds (this was with .45-75 W.C.F. cartridge with 350 grain bullet) with no effect. They restored the missing link then went through 6 more trials starting with a charge of 105 grains of black powder, behind a 700 grain bullet! The comment "worked well" is noted. They then increased the charge of powder to 165 grains behind 3 bullets (1,150 grains) and that "worked well." From there, they increased the powder charge to 203 grains and added more bullets until they reached 1,750 grains of lead (five 350 grain bullets). This also "worked well." Finally, they added one more bullet, bringing the total weight to 2,100 grains, and things began to happen. The comment was, "Breech pin slightly bent. Arm working stiff." The seventh and final test was again 203 grains of powder but this time six Martini bullets weighing 480 grains each (2,880 grains) were used. "The charge bent the breech pin, blew out the side plates, split the frame and otherwise disabled the arm," was the comment. Oliver Winchester noted that in this seventh trial, the shell had burst into fragments and the escape of gas at the breech did the damage."
Now I love the toggle link design. It is stronger than most of us give it credit for and it is capable of hefty abuse with black powder and equivalent substitutes. It is not designed for extended firing with substantive fast burning smokeless loads that consistently exceed 29,000CUP (even with modern metallurgy and quality control evident in Uberti and other reproduction mfgs). John Moses Browning (GRHS) fixed that in the Model 1886 with the vertical lock system. That redesign was pursued by Winchester because smokeless was coming and he and other major mfgs knew it. I work at APG, MD so I took the opportunity and asked a ballistics test engineer buddy of mine at the Army Research Lab about the toggle link design in Winchesters and even that later used in the Maxim machine gun. He told me that the toggle when closed just beyond top dead center creates a very strong lock. He said, "Dave, be real here. There are very few abuses at BP pressures of properly loaded cartridges that would ever wear that action down." He then explained that if Winchester had attempted the tests using say, turn of the century Varget, he never would have gotten close to the end stage of the test where multiple bullets were seated on one another. "The pressures generated with even the most forgiving smokeless powder would have caused deformation of the breech and catastrophic failure of the barrel just forward of the chamber." When he said that I got an image of a beautiful 1876 splayed out like a giant banana peel. He finished by saying, "If you want to shoot smokeless on an 1876 go ahead, but use Varget or IMR 4895 and work up loads slowly and never exceed 29000CUP." He offered to drill a hole in the barrel of my .44-40 Henry and insert pressure sensors, recreating Winchesters test using current gun proofing test protocols, if I didnt believe him, " so long as ya don't mind me junking your rifle", but I passed on his offer.
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