Schmeisser GmbH v. AC-Unity — Federal Circuit Revives Firearm-Magazine Patent

Background

Schmeisser owns U.S. Patent No. 10,866,045, which covers a housing for a firearm cartridge magazine. The claims describe several distances within the magazine housing and a ratio derived from those measurements. Schmeisser accused AC-Unity and another company of infringing claims directed to that structure.

The district court held the distance-related claim terms indefinite. Although the court could identify and measure the claimed distances in a completed magazine, it reasoned that the patent did not tell a skilled artisan what particular values would produce an operable magazine without jamming. That ruling led to partial summary judgment for AC-Unity and dissolution of a preliminary injunction that had previously protected Schmeisser.

The Court’s Holding

The Federal Circuit reversed the indefiniteness ruling. Chief Judge Moore explained that definiteness asks whether the claims, read with the specification and prosecution history, inform skilled artisans of the invention’s scope with reasonable certainty. Here, the claim language defined each distance, the specification depicted the measurements, and conventional tools could measure them. The prosecution history reinforced that conclusion: Schmeisser had amended the claims to overcome an indefiniteness rejection, and the examiner could apply the limitations when evaluating prior art.

The district court applied the wrong patent-law requirement. Whether a skilled artisan can choose the precise dimensions needed to build a working magazine concerns enablement—whether the patent teaches how to make and use the invention—not definiteness—whether readers can tell what the claim covers. A person could inspect a magazine, measure the specified distances, and decide whether it fell within the claim even if additional engineering judgment were needed to make a successful product.

Because the erroneous claim construction drove the other rulings, the Federal Circuit also reversed the related partial summary judgment, vacated the order dissolving the preliminary injunction, and remanded. The court exercised pendent appellate jurisdiction because those rulings were inextricably tied to the appealable injunction order.

Key Takeaways

• A claim can be definite when its boundaries are measurable, even if the specification may leave practical implementation choices to a skilled artisan.
• Courts must analyze indefiniteness separately from enablement and written description, despite overlap in the evidence.
• Prosecution history can strongly support definiteness when an examiner accepted amendments and successfully applied the resulting limitations to prior art.

Why It Matters

The decision draws a useful line for patent owners and accused infringers. Patent claims define legal boundaries; they do not necessarily function as complete manufacturing instructions. Treating every possible implementation gap as indefiniteness would collapse distinct Patent Act requirements and invalidate claims for the wrong reason.

On remand, Schmeisser’s infringement case and the preliminary-injunction dispute return to the district court without the indefiniteness ruling that had ended them. The nonprecedential decision is still a practical reminder to frame claim-scope arguments around what a skilled artisan can identify, while reserving operability and construction questions for enablement.