Since this is the Pistol & Revolver / Ruger Rimfires section of the Ruger Forum, I'm figuring you're referring to the Mark series of target and outdoor pistols. To me, there are several things that make an extended magazine less than desirable for that type of pistol. One of those is the obtrusiveness of something large and heavy hanging down from the grip of an elegant pistol like the Mark series. Poor balance and poor holster carry characteristics result. Another one is the engineering needed to make a large capacity .22LR magazine work properly. A staggered column rimless cartridge magazine can be perfectly vertical. Rimfire cartridges in a box magazine 'tip' at a certain angle, due to the large rim. There's also the transition from double to single column section that would need to function perfectly. The Mark series pistols are intended for sporting use, not military or law enforcement, where high-capacity magazines are often a true necessity. I'm figuring that you favor a huge capacity rimfire pistol magazine so you can indiscriminately blaze off a few dozen rounds at one time. Do note that it takes the same amount of time to load each round in a 10-round magazine as it does a 30. Maybe a belt-fed rimfire pistol would be best for those would prefer 'blazing away' hundreds of rounds in a few minutes?
Here's some info on hi-cap rimfire mags: https://www.ammoland.com/2015/01/kel...#axzz4eGVfKeil A Double-Stack Magazine For Rimmed Cartridges? - The Truth About Guns