Vintage Randall 12-6 kit knife

Here is a model 12-6 kit blade that my grandpa did. He bought the blade in January 1969 for $16.00! Grandpa used stag and did finger grooves, brass single bolster and brass butt. He was a proud NRA life member and put his life member pin on the butt.

How is the butt cap attached?

As far as I can tell he likely threaded it some how and attached it to the tang he was a tool and die machinist.