I must admit, I was  lucky enough to be able to stock up on PMI magazines in the 1990s and never had to worry much about finding after market rifle magazines for the Mini 14.   While admit I have seen plenty of poor performing Mini 14 rifles on the ranges, it was always because the user was not using Ruger factory rifle magazines.  If you are fortunate enough to live in a State that allows the use of semi-auto rifles for deer season,  there is no lighter and faster Carbine for Coyote or white tails than the Mini 14.   I have personally witnessed deer being taken with 75gr HPBT with the Mini 14, so don’t tell me the .223 isn’t good for the job.
Inside of 200yds and with a 4x optic, a Mini 14 is well within the tolerances of being able to take a 150-200lb animal.   Considering the flat trajectory, hold overs are virtually none existant at these ranges.  Since you can get 20rd and 30rd factory magazines for the Mini 14 again.   There still are reasons to not want to heat up the rifle and it is well known that the Mini 14 is not a military rifle.  The accuracy will begin to decline after approximately the 3rd shot is fired which gives good reason to only stick with the factory 5rd magazines.