Just curious if anyone has sent out their used AR bolt to have it hard chromed?  I'm interested in the place and price.  Thanks

I wouldn't think adding a layer of chrome to an existing finished bolt would work out well as it would likely throw off the tolerances.

I know these existed for a while in the military in the early 80's and went away

A hard chromed bolt carrier will work just fine.
The change in dimension of the BC after plating will be negligible within the upper receiver.

I think the reason you don't see it much is that there are better surface coatings (TiN for example), and the cost is about the same, or maybe a little bit less.

Anybody remember how great Armoloy was in the 80's (I had a couple of pistols done that still look good)? NiB made Armoloy obsolete for firearms (but Armoloy is still used in industrial applications).

If you are interested in hard chrome plating you should definitely give it a try. It's never been as inexpensive as it is now (in relative dollars). It will look great, and you'll get to see how it holds up.
At worst it will wear off in 500 rounds; on the other hand it's just as likely it lasts thousands of rounds.
It's not going to hurt your BC.

BTW, Armoloy is an electrochemical application of chrome to metal surfaces. It looks almost exactly like NiB.

G.