I normally make a finial "nut" and thread the tang, but I have peened the end of the tang a few times.
You need to make sure the end of the tang is as dead soft as you can get it. Heat cycle with a small torch several times to not more than dull red. If you hit the transformation temp, many steels will air harden to a certain degree, peening will be impossible.
I then put the finished blade tip down in a large bench vise. Pad the jaws with leather, and have the tip of the blade resting on a thick lead block. Try to get the vise as snug as possible, and then use a very light ball peen hammer to peen the tang over the end of the butt cap.
You need to make the tang fit the hole through the butt cap very close fitting so minimal expansion is required to get a tight fit. Round over the end of the tang before peening, just like peening pin in a handle.
You can leave the tang end "button" proud above the cap, or file it flush and polish it up.
Hope this helps. Honestly, threading the tang and using a nut to secure the handle and cap is easier without the risk of marring the blade finish.......peening works though, is strong and doesn't require thread forming tools. I would only use a tough handle material like antler or a strong hardwood.
In my mind, the best low tech method for making a bomb proof knife would be an antler handle, steel butt cap and a peened thru tang......doesn't get much tougher than that.
Darcy