I can't claim any credit for the design, but here are some pictures of how I made a copper bopper (soft hammer) for flint knapping. Antler would have been used traditionally for this purpose, but if you can't get hold of antler, this is a quick and easy way to get something that you can start working with.
To start with, go to the annual Bushmoot, find one of the native Spamels and ask him nicely to let you have a bit of old lead pipe. He may well throw in a couple of copper end caps. Allow the lead and copper to mature for nearly three months then get off your behind and start doing something.
You will need a small ball-peen hammer, and another hammer.
Beat the copper end cap over the round end of the ball-peen hammer until you have moulded int into a roughly hemispherical shape.
Cut up some lead into small pieces...
...and put them into the rounded end cap. You could use a pan to melt the lead, but the end cap forms a nice crucible and you don't then need to pour the lead.
Melt the lead using a blowtorch (remembering to avoid breathing any fumes), and leave it to cool down. The remnants of a bow-drill hearth board form a good cup to support the cap while it cools down.
Whittle a piece of wood into a suitable handle so that the end cap is a nice tight fit over the end of it...
...and glue the cap onto the end of the wood using epoxy or other strong glue and voila you have a copper soft hammer.
I'm still waiting for the glue to set, so I haven't tried it out yet, and the handle will need a little bit of sanding. I used a 22mm end cap, but for finer work a 15mm cap would probably be more suitable.
Thanks for looking.