Here is an interesting read, about testing the 45-70 trapdoors in 1879 which resulted in the Gov. going to a 500 grain bullet..."45-70 at Two Miles: The Sandy Hook Tests of 1879
by W. John Farquharson"...In the test they used faster twist barrels than the old 1-22, to stabilize the longer bullet. here is the exact quote...

"The report of November 13, 1879, lists the results of firing tests made at 3,500 yards distance with two long range Springfields. One had a rifle barrel with a l-in-18 rifling twist, the other .45-80-500 had a 19 5/8-inch twist. Two different loads were used: .45-70-500, and .45-80-500. The Martini-Henry .45-85-480 and the service .45-70-405 Springfields were again tested against a Sharps-Borchardt using the same loads as in the long range M-1873 Allin-Springfields. After firing many rounds, the service Springfield and Martini-Henry rounds failed to reach the target at 3,500 yards."

Here is the complete article:

http://home.earthlink.net/~sharpsshtr/CritterPhotos/SandyHook/SandyHook.html

I find it odd that a faster twist would not have been incorporated into the 1884 production guns to properly stabilize the new 500 grain bullets as tested....Now here is a thought, My 1873 TD numbers out to an 1883 manufacture, my Sons dates to 1886, His breech block is clearly stamped 1884 but it DOES NOT have the Buffington sight, it has a sight identical to my '73... and it also has 1-22 inch twist like my'73...I am still wondering if the "84's changed the twist and my sons barrel and sight is a left over "73... I would sure like to hear from someone who has an '84 WITH a Buffington sight....ED