I have my own opinion on this whole "DI" versus "piston" subject, but I won't get into it at this time. However, one thing I will say is that everyone who mentions Eugene Stoner's patent as some sort of authority on the use of the term "piston" in the context of an AR style rifle is wrong.
It is very well known in patent law that the person applying for the patent application can use and redefine words however they want in their patent. Just like some of you are sick of hearing people say something that (you think) is technically wrong, I am sick of people saying something that is legally wrong.
IV. APPLICANT MAY BE OWN LEXICOGRAPHER
An [patent] applicant is entitled to be his or her own lexicographer and may rebut the presumption that claim terms are to be given their ordinary and customary meaning by clearly setting forth a definition of the term that is different from its ordinary and customary meaning(s). See In re Paulsen, 30 F.3d 1475, 1480, 31 USPQ2d 1671, 1674 (Fed. Cir. 1994)
http://www.uspto.gov/web/offices/pac/mpep/s2111.html
So Eugene Stoner could have called his rifle's gas system a jelly doughnut system, and that would have been absolutely fine legally, and it would have been written in his patent. But that doesn't make his rifle's gas system a jelly doughnut system.
Joe Mamma

