I heard a myth about a tube fed 30-30. Basically if you load it with full metal jacket rounds, you risk detonating the round because of the recoil of a shot taken.

There is a possibility of a pointed bullet setting off the one in the tube in front of it.

That is why tubular magazine rifles use flat point, or round nose ammunition.

There are some newer cartridges that use a polymer tipped sharp pointed bullet, like the Hornady LEVERevolution.

Someone also did an article on this (Am. Rifleman? -- don't get too many of the "rags" any more). Turns out that the cartridges don't sit point-to-primer ( - - - - ) as we might think, but are tilted in the tubular magazine ( / \ / \ ). Not as extreme as that, but you get the idea. This is due to the diameter and shape of the cartridges and the tube (and the magazine spring as well).

Still, since it's POSSIBLE to line up cartridges in a mag tube, flat points are still recommended -- the newer soft polymer tipped offerings notwithstanding.