Round barrels were standard on both rifles and carbines, but most Model 1892 rifles ordered prior to 1900 had octagon barrels as the general belief was that the octagon profile was stronger.
Twenty inches was the standard length for the carbine barrel, and 24" was standard length for the rifle barrel, and in total about 66% of all model 1892s came with 24" barrels and about 33% came with 20" barrels with less than 1% having barrels of all other lengths.
A rifle with a barrel shorter than 24" was a "short rifle". Longer or shorter barrels on rifles and carbines could be specified as part of a regular order until 1908. After 1908 they became a special order only item. In either case, special length barrels were not common and comprised less than 1% of total Model 1892 production.
Octagonal rifle barrels were available on special order - but Model 92 carbines had round barrels - period. If you wanted an octagon barrel, you had to order a rifle or short rifle.
80% of all Model 1892s were chambered in .44-40 with 8% in .38-40, 7% in .32-20, 4% on .25-20, and less than 1% in 218 Bee.
Saddle rings on the Model 1892 used a u shaped double staple stud. The screw in type stud found on the Model 1886, Model 1894 and Model 1895, as well as on some of the Model 1886 and Model 1873 carbines were never fitted to the Model 92, so if you find one with a screw in stud, it's been added after it left the factory.
Similarly, if you find a SCR with a barrel shorter than 20", be aware Winchester only made about 1200 of those, so the odds are that it was shortened after it left the factory. Same with a Model 1892 short rifle - Winchester only made about 800 of them. Model 1892s had a bad habit of developing a ring in the barrel under the froth sight, so it was not uncommon to shorten one to remove the ring and improve accuracy, so the odds of finding a post factory modified rifle or carbine with a shorter than standard barrel are much higher than the odds of finding an original.
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In that regard, a 24" saddle ring carbine (round barrel by default) is a possibility, but would be quite rare, since fewer than 1% of carbines (less than 1200) would have a non standard barrel length, and those would be more likely to be shorter, not longer. It's slightly more likely that you might encounter a 24" rifle (round or octagon barrel) as they were 66% of the Model 1892 production, and the only special order item would be the saddle ring. But again, check to be sure it's got a u shaped stud, not a screw in stud. Given the use of a saddle ring, it would be more likely to see one on a short rifle than it would be on 24" rifle, just because of how it was used. If a customer ordered one on a 24" rifle, he'd have done it just for looks, not as a practical accessory.