Interestingly, the cover sheet for this patent is missing, which contains most of the pertinent information for calculating the expiration date of a patent. However, from checking the information available on Google Patents against the content of the grant, we can calculate the expiration date using the following information:
Publication date: May 17, 1977 (this is the Grant Date)
Filing date: Mar 18, 1976 (this is the filing date of the application)
Priority date: Oct 31, 1974 (this is the filing date of the earliest related application)
This is a continuation of application Ser. No. 519,561, filed Oct. 31, 1974, now abandoned.
The above statement indicates that this grant is claiming a "domestic benefit" of an earlier application, which sets the priority date to October 31, 1974.
The USPTO provides an Excel spreadsheet that can be used to calculate patent expiration dates, as long as the dates occur after the 1930's. Using the above dates, we find that the patent expired on October 31, 1994. Since then, the invention that was claimed is now in the Public Domain and may be manufactured and sold by anyone without licensing it from the inventor. The patent can no longer be reassigned.