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High Arch, High Comb breech blocks in 1873 models
Posted by John Shonafelt on Sunday, 13 December 2015, at 10:44 a.m.
Some of you have I'm sure already know this, and to others it will be a bit esoteric, but it is new and interesting to me and I thought I would share it. I recently purchased an 1873 carbine s/n 40258. It has the 1st type block and I have noticed the hammer falls slightly over the top of the comb of the block. To my eye it seemed decidedly "un-Springfield". In my experience with various Springfield models I have owned are that hammers hit cones and blocks very centered and very precisely angled on original specimens. It seemed likely the carbine may have originally had a high comb block but the serial number range given for the type 2 block seemed to be not clearly explained and most 73 carbines I have seen have had the 1st type block.
After some searching, I did find evidence that the high arch, high comb blocks were fitted starting in January of 1875, and thus was very likely what was originally fitted to my carbine. While comb dimensions are not specifically given, the general information is well presented in Ordnance Notes number 48 published March 9th 1876. This particular note is called "CALIBRE .45" RIFLES AND CARBINES DAMAGED IN SERVICE" and relates to problems associated to the breech-block not being locked at the moment of ignition, resulting in the blowing out of the cartridge head and the throwing open of the breech-block, with catastrophic results noted for carbines 16338 and 21718 (both resulting in broken hinges). The note describes material design changes to the firing pin guard (3 thumb piece versions), the breech block, and firing pin.
Also of interest, I had always assumed the comb of the breech block was increased in height to obviate peening/cracking from prolong hammer blows. It turns out that is not the case, but instead it was to keep the firing pin guard from riding up on the block creating the possibility of a unlocked ignition, to quote: "A more effectual remedy was adopted for future manufacture by increasing the height of the comb of the breech-block sufficiently to render riding up of the firing-pin guard impossible. This modification began January 1, 1875, according to the books of the Master Machinist's office."
I love pouring over original resource material. Anybody ever seen the "books of the Master Machinist's office" that are referenced in the note?
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