A patent would not protect a particular model design, such as specifically a 10/22 magazine, but rather a technology.
The 10/22 rotary magazine patent 3,239,959 was applied to protect removable rotary magazines in repeating guns. This meant nobody else, from its issuance in 1966 until its expiry 17 years later (current law is 20 years from filing date), could produce firearms with detachable rotary magazines without licensing rights from Ruger. Comparatively, an internal rotary magazine would not have been applicable, or detachable magazines which were not rotary mags. ONLY removable rotary magazines were protected under their patent. This was not specific to the 10/22 magazines in any way.
So the technology has been free for use to the open market for 36 years.
Trademarks are different things.
Trademarks are a different game, as trademark registrations in the US currently last for 10 years each, with effectively infinite life through renewal. Renewal only requires demonstrated use or intent for use within the term. Other companies cannot then use these trademarked terms without permission from the registered owner. There is, in fact, a burden of defense for Trademark holders - if someone infringes, the registrant is obligated to defend it, else they risk losing the registration and ability to defend in the future.
For example - Ruger sued Kidd for selling products using the trademark protected “Ruger” and “10/22” without permission. Kidd can make and sell their “10/22 like” products, but cannot use “10/22” or “Ruger” in their models, on their websites, or in marketing without permission.
Ruger can charge for said permission. So if someone wants to make 10/22 compatible magazines and market them as such (for example, putting “fits Ruger 10/22” on the product label or website), then they have to tip their hat to Ruger, uphold the labeling expectations compliant with Ruger’s desires and registered trademark practices, and have permission from Ruger to do so - permission paid for or otherwise.
