Often an invention is a solution to a technical problem. So it makes sense for inventors to describe the technical problem they are solving in their patent application to help the Patent Office understand the contribution and relevance of the invention.
Unfortunately, Patent Office examiners and especially the Board of Appeal judges love to use the inventor's statements as reasons to bolster their rejections. As discussed in the blog post linked here (link), inventors need to be careful in how they word the recognition of the problem, or the specific unmet need that led them to their invention.
A key part of the invention was the specific design of the extractor that included a hook that was received by a pocket on the muzzle end of the bolt. Specifically, the claims required that "a bottom of the pocket is recessed at least a first dimension within a first range A that is greater than 0.130 inches and less than 0.200 inches in a first direction from the muzzle end of the bolt and the hook member has an axial thickness parallel to the center line of the bolt within a first range A' that is greater than 0.050 inches and less than 0.130 inches." In the patent application, the inventor explained that semiautomatic firearms have complex mechanisms that continuously cycle each time a round is fired and as such, certain components are subject to wear and must be cleaned and/or replaced on a periodic basis. Accordingly, the inventors explained that "it is desirable to provide a firearm ... that withstand[s] excessive cycling and thus extend[s] the useful life of such components in order to reduce the need for replacement."
The Examiner could not find any prior art that had the specific sizing claimed by Colt, but nevertheless found that it would be obvious to optimize the size of the pocket and hook as mere "design choice" since it was allegedly just discovering the optimum range. The Appeals judges used the inventor's statement quoted above about the desire to withstand repeated cycling as a reason to support the rejection. Specifically, they determined that "[w]ith this information as background, ... the record supports a skilled artisan would have had a reason to optimize the dimensions of the extractor hook (and the associated dimensions accommodating those changes) and, in particular, a reason to increase the size of the hook to provide more strength and durability."
What must be frustrating to the inventors here is that they never admitted that a skilled person would know to link the need for excessive cycling to the particular shape and sizes of the hook and pocket as claimed.
The moral of the story is that while it is beneficial to give the background to your invention, you should do it in a way that does not give the judges an easy way to use your words against you. As explained in the post linked above, you should always preface such information with the statement that the issue or need was "recognized by the inventors" and is thus not admitted to be generally known by the skilled artisan.