Update, July 22, 2014:

After a week of rain, finally got a mostly dry morning to go to the range to test the two modifications I had done: 1. removed Loaded Chamber Indicator (LCI) and 2. slightly rounded the front square corner of the rear magazine lips. I had read (and watched youtube videos) for quite a few hours exploring the failure to feed properly issue, and there was no lack of people with suggestions. When I checked the amount of force that was required to move the LCI, it seemed to be more than I suspected (some people claimed that a less than freely moving LCI could cause chambering problems) was necessary, but since I have no other Ruger Mark III to compare it to, it may have been the normal pressure. I removed it.  I numbered all my magazines (3 Ruger factory mags, 3 Mec-Gar) and rounded the front of the rear lips of 2 of the Rugers and 2 of the Mec-Gars as per photo below. Quite a few people claimed that helped feeding problems with their Mark IIIs due to possibly too close a tolerance interfering with the fixed extractor ejector and/or the rim coming out of the magazine.



Even though I had 4 kinds of .22LR ammo, I chose to use only the stuff (Federal Target Grade Performance) that I have enough of to shoot the next Steel Challenge match (and which is what I used in the last match when I had all the problems), and see if I could get that to work. I shot five rounds per magazine, multiple times. The two altered Ruger mags worked perfectly through 25 rounds each. The one unaltered Ruger mag had a couple of failures to feed in 20 rounds. One unaltered Mec-Gar mag didn't work well at all, the other two had 3 or 4 FTFs in 25 rounds. This was a dramatic improvement over what had happened in the last Steel Challenge match wherein I rarely if ever got off 5 rounds without an FTF. I looked very closely at the mags having problems and decided to bring the front lips slightly closer together on a couple of them as they seemed slightly wider than the perfectly functioning mags. It may have been only a few hundredths of an inch, but they worked slightly better once they were closer, especially the one where one side seemed way too wide. So, way better overall.

Went home and finished with the other mods: 1. removed magazine disconnect safety, installed Tandemkross Magazine Disconnect Bushing (I was prepared to use the super cheap washer technique, but decided to splurge and spent the $10 for the bushing), and 2. replace existing extractor with Volquartzen Hard Edge Extractor. So, over 4 (FOUR!) hours later... JFC... at least half of which was spent watching and re-watching and re-re-watching re-assembly videos (where's the damn third hand and special bent-nose tweezers when you need them?)... it was all put back together! Nothing to it! I learned a lot! I also modded the remaining two original square lipped magazines and sanded the newly rounded corners down nicely with 600 grit sandpaper. (Also polished the sear, hammer, and trigger plunger a bit).


Went to the range this morning.  I also made sure to check the alignment of the first/top round in each mag prior to loading into the mag well.



Put 35 rounds through each magazine in sets of 5, shooting at my steel plates. 210 rounds.100% perfect. Not a single FTF! Woohoo!  Of course I don't know for sure what part each mod played in correcting the faulty feeding... it may have been that I just needed to clean the gun better or remove excess Frog Lube or who knows? Anyway, I'm going to be practicing a few more times before the next match, and if I have any problems I will update.

Thanks to everyone who took the time to make suggestions and offers of help. If anyone has similar FTF problems with a Mark III I'd be glad to share the sources of my information though most of it is pretty easy to find.