This letter will help collectors better understand how partial collar error coins were created. I was not convinced that planchets might over-expand during improper annealing, but the Coiner (Bosbyshell) says that is the most likely cause. Since Snowden had been Coiner several years earlier it's unlikely Bosbyshell was stating anything new.
April 21, 1884
Hon. A. Loudoun Snowden,
Superintendent
Sir:
In response to the letter of the Rev. J.A. Boyce of Stony Fork, Tioga County, Pa, addressed to you, enclosing a half dollar of 1877 struck in the Mint at San Francisco, handed to me for examination and report, I have the honor to state that in my opinion the piece is a genuine coin. It is one-1/10the grains light of standard weight, and resists the acid test.
There are two reasons to account for the appearance of the periphery – the most probable one is that the planchet became enlarged by overheating in the annealing, and was forced into the collar by the upper die – the lower dies striking it a moment later than usual.
The other reason to account for the trouble is the lower die may possibly have stuck in the collar after rising to enable a piece to become disengaged, and the upper die descending before the lower die loosened, forced only a portion of the planchet into the collar.
[RG104 Entry 1 Box 131 via NNP]