I would like to use a hard chromed b/bc in one of my ar's but I have heard it can cause accellerated wear on the upper receiver. Is this true? Is it enough to really matter in a semi gun? Seems like it would make it easy to clean and reduce friction. Any thoughts from people who have used them? Thanks in advance!

Pretty much a waste. Wont improve a thing.

The one thing to remember is that the chromed bolt starts it life as a normal bolt/carrier, then chromed.  The chrome builds up the bolt/carrier, and if installed in all ready tight upper. It will cause binding and addition wear until the bolt has mated with the upper.

As for cleaning, it's just easier to spot the fouling.  The gas chamber on the non chromed carrier is already chromed,so only outer is given a layer of chrome.  That is unless the chromed is polished, then the fouling will wipe right off.

P.S. on some of the chromed bolts, you will need to lap the key into the carrier to assure a tight seal.

Roger on the above, plus:
As the plating wears off (and it will) the flakes will cut into the aluminum sides of the upper.  Had an original GI bolt/carrier assy 20 years ago. Sold it to an Atlanta Braves ball player who just had to have it. Told him what I just told you, but he insisted on buying it, because some of the other Braves had ARs with unplated carriers and he wanted to show them up.

Go figure???