I have and run alot of Old Colt straight 20 rounders love them they have had no issues that I have had with 30 round mags. Being in NY I have to use the preban stuff these colts run like a top.
Doc,
You haven’t heard lots of complaints because the 20s work. I have a box of 100 USGI surplus 20s at work and the only ones which give me problems are the ones with obvious damage (they just plain look damaged or out of spec). Most are without finish and many are marked Colt AR15 with a mixture of other types.
I believe it was written that 'Gene Stoner said the 20s were perfect but the 30s were designed because GIs were complaining about the mix-match in capacity vs the AK47 during Vietnam.