I used a low melt solder made for pot metal/zinc.
http://muggyweld.com/
Super Alloy 1
Some nice videos there that make it look easier than it is.
I did fill the tops of the receiver rails, ejection scallops, feeder clip notches various holes etc.
The best way to do it I found is to use the cut off barrel material and make a waste mold from plaster or the like to first make cast pieces to dry fit the areas, then use the solder to attach the new metal and blend blend blend.
I attached the unique Carson's lump, - The bolt weld area this way as well. I first shaped the "lump" according to the stunt and production pics and then soldered it in place.
It is not for the faint of heart. Although it melts at a lower temp than the Zamac it is dicy and can warp or damage your frame if not careful.
It does not always stick well if you get it wrong. As with any soldering or welding... clean clean clean...
It does blue as well so that is a plus.
I really didn't want any plastic or filler on this model for some reason... it was a challenge.
Also no glue on this replica at all.
The Hammer is cast off a real vintage C96 hammer. I made a mold and cast the cut off barrel material... very hot casting.
I made a waste mold first and re-sculpted the bottom pivot area to match the MGC mechanism so it works with the trigger and safety and then cast the MGC Zamac. It has the "S" and also the 813 stamp to match the serial number.
The top of the bolt also has the etched "Crown U" markings and 813 serial number.
I tried to make it look old and used and worn.