Can someone explain...

[Navy Six]

Since the weather broke a bit today, I took a 1996 vintage Pietta 51 Navy(.36) out to shoot. When I got home and took the gun apart to clean, I noticed one of the frame pins had sheared off, with one half staying in the frame and the other half in the barrel lug.  For some reason I put a magnet on the half in the barrel lug and it came right out. On closer examination, I noticed the pin was not solid but had some type of "core" with a metal jacket surrounding it. I can only compare it to a copper jacketed bullet with a lead core. The part that stayed in the frame looks identical. The "jacket" is very even and a noticeably different material. I have never had a pin shear off like this so I've never had to drill one out of the frame yet. I bought the gun brand new so I know the pin is original.
My question is this: Is this how these pins are normally constructed? I was just surprised at what I found.

[Tuolumne Lawman]

All the ones I have seen have solid steel pins....

[Coffinmaker]

PLUS ONE too The Lawman.

I have seen the pins come out of the frame.  I have not had one that had broken.  What you describe, sounds to me like a steel pin with a crystalized center.  There would be no economic reason to make a small part like that out of two different materials.

[Major 2]

"...sounds to me like a steel pin with a crystalized center. "

ditto ...I think Coffin maker is spot on

[AntiqueSledMan]

Hello Navy Six.

Sounds like a case hardened pin to me, when parts are case hardened only the surface is hardened.
I know on a Thompson Shaft (Trade Marked) when you face it off, the end will give the appearance
of two different materials. I'll bet the center is soft.

AntiqueSledMan.