I am sure Jason B will be along soon to show how he does it very effectively.

I believe he uses an electric engraving tool.

Phil

As Phil says both myself and Ramon tend to use an engraving tool to add a "cast" testure though this is more on softer bronze/gunmetal than iron. I'm not sure if they are made these days but we both have the Wolf engraver.

As you can see from the shiny bits this carb casting has had a fair bit of reworking

And after a bit or retexturing

I have in the past done small areas with a ctr punch just holding in my hand like a pin and tapping on the surface.

Now having said all that is a "sand" texture really right on a 1/12th scale model? On something like that I would be aiming to have little if any sand texture still showing just a few undulations so it still looks like a casting. Have a look at my comments here and also the post before about finishing castings on a 1/2 scale model that prompted the question.

Just google Burgess engraver or Burgess vibrio tool and you will see lots of electric engravers.

Another alternative is make a stippling tool, you can do this using silver steel and make the end look like diamond knurling with a three square file, slightly dome the end as well. This is much easier if you have a metal chequering file as used by the gun trade.

Hope this helps John