Yes it's Rock Maple.
The customer ordered that way and I can't say I'd disagree with him. It's pretty, but the real reason for it's use was it's density and strength. The weight is 22 pounds. It's "too light" too.

I test fired the barrel after it was breached, but I told Ken that I would accept his order but I would not zero it. Ken was over 400 pounds. I am 185. So I could not have done it anyway. He did shoot it with up to 300 grains of powder, but the gun would handle up to 750. Such a load would be only for someone like Superman to fire as the recoil would probably be like getting hit by a car.
With 300 grains it would back Ken up over 3 feet.

The side plate and the comb-plate are both to add weight. They are made of heavy plate. There are 2 (or maybe it was 3) "dead-Mule recoil reducers in the butt. Even the grip cap was made of thick metal. All in get the weight up so the recoil could be dampened. From what he told me, it didn't work very well. It's just all I could do without making the gun so big around that you could not close a hand around it.

Colin Stolzer (now in Washington Kansas) has now made several 2 bores including a double breach loader, which is what the shell in the first post by Ripp goes too. He has learned a lot about such artillery. I dare say he has now become the foremost authority on them.

https://www.youtube.com/watch?v=uv6Z7rRYtPU

But be that as it may, I was the 1st one to make such a monster for "sporting use". All others we were able to document were mounted on boats or were wall guns.
Colin goes by CowboyCS on this site, but I don't see him here very often.