In response to this thread www.ar15.com/forums/topic.html?b=3&f=17&t=168189 i went back to the store to check out the brand and see if it was worth buying simply for the LCF.
Ok, the bottom of the mag read: "For Mini-14, AR-15, M16...) But to see how nice (or dumb) it would look, I asked to see an HBAR Colt Carbine that was hanging from the rack behind the counter, and now the strange thing happend:
The Mag would NOT FIT! It wouldn't even insert into the mag-well! It was too big lenghtwise. Bothj me and the dealer tried, everywhich way. and we switched to a bushmaster but it wouldn't fit.
However it went perfectly into the Mini-14!
What? Don't those two use the same mags???
Can someone explain whats going on here?
Thanks

The mags are different.  The contact points that hold the magazines in battery (right word?) are different on the two magazines.  The Mini 14 magazine swings into its locked position (with attachment points on the front and rear of the mag), and the AR 15 slides up into what should be a snug mag well before locking (with the mag catch on the side holding it in).  Neither mfgs mags will accomodate the others mag well (at least judging by the contact points).  My guess would be that the Ruger system allows for a longer magazine, while the AR will hold a mag that is a little wider.