Re: I have made a terrible mistake.
Holy Cow!! A Mini Ranch I bought for my brother years ago is still going strong. I gave him the rifle and 5 or 6 factory mags with it, and he never reported any problems. Unless Ruger quality has deteriorated that much it should be a great SHTF choice. Should shoot as hard, fast and accurately as most off the rack ARs in the same caliber.
You can build most any rifle into a 'tack-driver' - I'm talking off-the-shelf mass produced short barreled ARs. I have 3 and they shoot just fine, but are not target guns. They are short range (under 200 yards) defensive weapons.
2 pennies more - I've bought aftermarket mags for my M1A and M1 Carbines that were absolute trash. Ended up saving the springs and followers for spares and tossing the rest. I'm a firm believer in having at least 6 hi-quality mags for any semi-auto I own.