The Federal Circuit reversed a district court’s claim construction concerning a patent directed to a retrofit assembly for converting a semi-automatic rifle with a detachable magazine, such as an AR-15, to one with a fixed magazine to avoid regulations on assault rifles.

The claim of the patent recited “a magazine catch bar.” Given its ordinary meaning, the use of the term “a” would include both factory-installed magazine catch bars and magazine catch bars that were part of the new retrofit assembly. The “catch” was that another independent claim recited removing “the factory installed magazine catch bar” and then installing “a magazine catch bar.” Similarly, the specification stated, “The invention is a permanent fixture added to a semi-automatic firearm by removing the standard OEM magazine catch assembly and installing the invention.”

The district court reasoned that “removing” the bar and “removing” the assembly conveyed that none of these parts could be “a magazine catch bar” as later recited. And, since the same term when used in different claims generally has the same meaning throughout, the district court held that all claims reciting “a magazine catch bar” excluded OEM-bars.

The Federal Circuit disagreed. It held that the use of the indefinite article “a” meant that the “magazine catch bar” could be either the OEM-bar or a new-bar, which is the ordinary and customary meaning . It reasoned that “[a]n instruction that identifies the removed assembly as including a factory-installed magazine catch bar, which focuses the process on conversion of what came from a factory, does not imply any preclusion of reuse of the same bar as one part of the assembly being installed in place of the removed assembly. The ordinary meaning of the claim language allows the factory-installed magazine catch bar to be removed as part of the initial assembly removal and reused as part of the assembly installed in a later step.”

The Federal Circuit also felt that restricting “a magazine catch bar” to new or different magazine catch bars would read additional limitations into the claim. Rejecting an argument that because the claim failed to use antecedent-basis language such as “said” or “the” meant that the two magazine catch bars must be different, the Federal Circuit noted that “[t]he use of antecedent-basis language … would have narrowed the term to cover only a factory installed magazine catch bar” and “[t]he inventors, in the independent claims, did not choose to claim a device with a ‘new’ or ‘different’ magazine catch bar, but instead a device with ‘a magazine catch bar,’ which, by its ordinary meaning, could be either the removed catch bar or a new or different catch bar.”

Because the accused infringer conceded that use of an OEM-magazine catch bar was its only basis for noninfringement, the Federal Circuit reversed both the summary judgment of noninfringement and the denial of the patentee's cross-motion for summary judgement of infringement.