I nerfed it to scrap iron armor stats, so its the lowest tier heavy armor right now.
Cralification: I'm reading this as that the mining helmet armor will be made equivalent to the scrap iron helmet armor rating? No changes will be done in terms of what armor type it is classified as right now, right. Since in A17.4 it's classified as light armor. See image.
https://imgur.com/tQ75bW2
The Plastic Plating mod which is a light armor mod can be put into it. So right now in A17.4 in helmets it goes like this:
Light armor
Padded hood = 2 armor rating + repair w/ cloth
Leather hood = 4 armor rating + repair w/ leather
Football helmet = 8 armor rating + repair w/ forged iron
Mining helmet = 8 armor rating + repair w/forged iron
Military helmet = 6 armor rating + repair w/ military fiber
Heavy armor
Scrap helmet = 5 armor rating + repair w/ scrap iron
Iron helmet = 7 armor rating + repair w/ forged iron
Steel helmet = 9 armor rating + repair w/ steel
SWAt helmet = 10 armor + repair w/ forged iron
The values listed are all base amor with no perks or armor mods installed. I hate to say it, but you're gonna have to put the balancing issue again @madmole. Sorry.
Edit: Two ideas I can think of, 1) remove the mining helmet as a head slot and reintroduce it as a armor mod or 2) have the mining helmet replace the model the iron helmet and keep the stats the same.