There is a rifle for sale in EE, the seller noted he only shot Black Hills Gold moly ammo through it.  Someone replied with this comment:

"It's too bad you've shot moly through it... That means anyone who wants it would have to use moly as well."

Could someone explain this comment?  I was not aware of problems associated with the use of moly coated bullets.

That's not totally accurate. You'll just have to clean it super well, several times before you shoot it. There's a layer of moly built up in the first 1/3 of the bore, so you need to get that out of there. Scrubbing with a good solvent, is the only way I know to get it all out. Even then, you might not get it out completely. Don't shy away from the gun though, and don't feel you have to shoot moly bullets through it. Copper, or coated...Pick one or the other, but don't alternate.

Quoted: There is a rifle for sale in EE, the seller noted he only shot Black Hills Gold moly ammo through it.  Someone replied with this comment: "It's too bad you've shot moly through it... That means anyone who wants it would have to use moly as well." Could someone explain this comment?  I was not aware of problems associated with the use of moly coated bullets.

marvl,
if that rifle was an ArmaLite AR-10(T) or the AR-10A4 with an SS barrel (or for that matter any ArmaLite rifle with an SS match barrel), the seller is following established ArmaLite recommendations.

Edited to add:  I do not disagree with Robar's comments above as the ArmaLite match rifles, like most match rifles, are shoot-and-clean after each 20-rounds and that's after doing the proper break-in procedure.  (Sure are accurate rifles !!)