Quoted: Has anybody used the 30-round magazines from Center Fire Systems? I have four original M2 magazines but wouldn't mind putting away about 10 more while they are available. Also.... can anybody recommend any others out there that are reliable 30-rounders? thanks, Ron

The following pertains ONLY to genuine USGI mags.

Reliability issues with Carbine mags are primarily due to tired, worn, 50+-year old springs.  If your mag, esp a 15-rd mag does not work, and the mag itself and the mag latch seem to not be otherwise mechanically defective, replace the spring.  While the mag's disassembled, clean it inside and out, and apply a coating of automobile wax as a preservative for the bluing.   Note that USGI mags were always blued.  Very lightly lube the new spring before installing.

When using the 30-rd mags, make sure that your carbine has the late-style mag latch installed, the one with the extra little latching point for the 30-rd mags.  The late style latch can be used with 15-rd mags also.  Failure to use the later latch in conjunction with 30-rd mags will cause problems, no matter how good the 30-rd mag is itself.

Note also that the 30-rd mag has a hold-open style follower, while the 15-rd does not.  These followers are interchangeable, and you should standardize on one type if using the carbine for serious purposes. I much prefer the hold-open type, but YMMV.