I've made no modifications to any of my magazines and the 17 FB functions very well with up to five rounds in them.. Haven't hand the urge to do a mag dump but did have a trigger malfunction once and dumped three faster than it was supposed to. That was all in the gi mag or they may have all gone down range.. Just make sure all cases are as far back in the mag as possible, slap your helmet style.
To the original poster, if the 17Fireball is something you want, its not that complicated to make your own brass. 221 brass sized down or start from scratch with 223, neck split 204, 17 Rem or 222.