You've slightly misunderstood the law. Hardly surprising when you read how much of a dog's dinner of contradictions it is.
FIXED magazine .22 rimfires (such as "cowboy lever action tube fed") .22s are exempted, not ALL .22's are exempted. If the magazine
is detachable it's covered (unless you either bought it out of state or owned it already & can prove it.)
Example:
You have a Ruger 10/22 & you BUY, ASSEMBLE, or TRANSFER a detachable magazine (regulated high capacity bullet feeding device) its illegal IN THE STATE OF MARYLAND. (The limit is 20 rounds untill Oct 1St after that it drops to 10 rounds) It is NOT ILLEGAL to own, use or import such a magazine (unless you broke other laws creating it).
*notice my carefull use of highlighting, its intentional.*
Now Its not illegal to own, posess, or use magazines with a capacity above the current limit. Any magazines you CURRENTLY LEGALLY own are grandfathered in perpetuity (or untill the change the limit again)
The idea was to protect lever action .22s from becoming quasi-semi-demi illegal, but they messed it up as usual. If you want 20-round detachable magazines get them before Oct 1st then they're legal to get within the State of Maryland. . After that you can only get 10 rounders legally BY PURCHASING TRANSFERRING OR MANUFACTURING them IN THE STATE OF MARYLAND.
*wink* wink* Nudge* nudge*