A question for the original poster. Is there a specific reason you want a metal core cane?
If it is only for the idea of a stronger cane, the metal core is not really needed, but can lead to a can of worms if you do indeed use it for a self defense situation, and seriously injure/kill someone. A cane such as that will fall under the "loaded cane category of pre-prepared weapon. This is not something that you want happening in court. A cane/walking stick made out of ironwood/hornbeam, or Bois d'arc like has been suggested, will stand up to any strikes against an attackers anatomy.
I've been in court as the aftermath of using a heavy hornbeam hiking staff on a off leash pit bull and it's owner that attacked our Welsh corgi, and the owner who attacked me. I was not the one hit with the criminal charges, but it was a civil suit against me by the owner of the pit bull for his dogs death, and his injuries. He told the judge that the fact that I was walking around with a "weapon" indicated I was the aggressor looking for a fight. At the time I was in my 60's, and I am rated 50% disabled by the V.A. for injuries to my right food and ankle from active duty in the army. As a result, I do walk with a cane all the time. When I go for a walk in the woods with my family, I substitute a hiking staff for the cane.
In court, his lawyer presented his case against me, saying that I used a weapon to kill his clients pit bull, and inflict serious injuries enough to require transport to the ER.
I presented my hornbeam hiking staff for the judge to examine, and the judge did indeed examine it, and stated that it was not a prepared weapon, and that it was clear defense of our dog and myself and then threw the case out of court. I will never forget the judge's choice of words about a prepared weapon.
For legality, it is a very bad choice to "load' your cane with any metal. You loose the "plausible deniability" factor. You don't want to do that. It's not the criminal charges you need to worry about, but the civil suit after. Like O.J. Simpson, he faced a whole different ball game after he got off of the criminal charge, but ended up broke after the Goldman family lawyer got done with him. A plain stick, all wood will give you that very very vital plausible deniability that you will need after the event.
If a plain wood hornbeam staff could enable a mid 60's white haired senior citizen 5 foot 9 inches and 165 pounds, crush the skull of an attacking pit bull, then take down the attacking outraged owner who was a bit over 6 foot shaved head tattoo'ed 30 something guy, you won't need a metal core cane.
The staff shown next to one of my EDC canes, is just over 4 feet, and is 1 5/8th diameter on top and 1 1/4 at bottom. The judge liked it. Like all my sticks/canes, there is no metal anywhere, and my sticks will go right through TSA security.
BUT… I do notice that when I travel by air, they always x-ray my cane to see if it's hiding anything. I think a metal rod inside will cause you great trouble at the airport.