I achieved a similar ish effect by using textured rustoleum as a first layer then filler primer on top if it before putting the desired metallic color on top of that.

Truck bed liner spray paint is the go-to for proton packs, should work for this too

Off the top of my head I would think:

• adding bondo, or some sort of filler,

• dabbing it with a sponge/crinkled up foil, etc before drying

• sanding down for a uniform height but leaving enough divots and pitting to get that effect when painted.

Check out SKS Props on YouTube. He’s done a number of armor builds that have this rough raw metal texture and his videos show exactly how he does it. The Fallout, the Gears of War, builds like that have that kind of finish.

This might get you close.

This anvil is printed in PETG, primed with Rust-Oleum filler primer. Then I sprayed it with Krylon faux stone paint, then covered that with matte black spray paint and rubbed it with graphite powder.

This is a stage prop, so the sand-cast texture is exaggerated to look right from a distance. If you used the stone texture lightly and sanded it down some, it might work.

You can use a heat gun to create dents by warping the helmet just be careful not to overdo it

For a soft dent, use a heatgun and the handle of a screwdriver or some other blunted tool handle. For a sharp-cornered dent, you'd have to cut directly out of the helmet and shape the dent yourself with the inverted piece you cut out. Glue it back in upside down and shape it with filler. For the texture, hit rhe piece with spray adhesive like Elmers or Super 77 first. It beads up. And don't be uniform. Cast-iron is rougher in some places and smoother in others.

2 part bondo, Thin with acetone. Cut the bristles down on a super cheap brush and use it to dab the bondo all over. Once it’s dry, get some 400 grit and sand all over just hit the high spots to flatten them a little.

Add it via blender before you print.