Marlin model 43 question

Hello all,

I Have a 12 ga Marlin model 43. The mag tube holds (5) 2-3/4" shells.
I bought it way back on ebay (before Gunbroker). I think it's an old Police shotgun.

Anyway , as I recall, there was supposed to be a unique loading procedure other than the standard through the bottom and direct into the tube. I've loaded it this way and it functions fine (still haven't shot it).

There is a lever/button on the end of the magazine tube that, when pushed in and simultaneously pulled, moves the mag tube forward toward the muzzle about 1 inch. It is the rturned by pushing a button on the side at the forward mag support and it snaps back into place.

I sure don't see the advantage in this. It dosen't look loadable in this forward position .
Is this a takedown procedure? If what is this for? Is there an alternate way to load this shotgun? I don't think you could carry extra loaded mag tube cause the mag end has no check (shell stopper).I'm puzzled.
Stan