I have been using 20 round mags lately and like them better than the 30.  I guess they are a lot easier to use on the bench and don't get in the way as much.  I'm sure 20 and 30 rounders are both reliable but I found a few marked as "Simmonds Prec. Prod. Inc. West Haven, CT" that work real well.  They have an aluminum follwer and work great with my Colt m-4.  I wish I bought more (only got two) because these things work well.  Anyone else out there have these mags?

I bought several 30's when I first got my ar. After a few outings, I too decided I like the 20's better. I only have a couple. I dont think the mags you list a very uncommon. All brands of USGI mags are reliable (I think there were some problems with 30 rd coopers at one point) and should give you the same performance as you describe with your specific brand.

You should be able to find plenty over at the equipment exchange.

A fellow over there who goes buy "79 Trans-Am" is a good one to deal with. I have purchased from him several times without any problems.