EA with J15,
This sounds like an Essential Arms lower receiver. They never made complete rifles so it's a parts gun. The receivers are cast and were the least expensive you could buy during their time of production, but they were/are one of the best cast receivers out there. They are kinda ugly though. Back in the day, we referred to them as "brail receivers" as the markings are raised above the receiver as they were cast into the mold as opposed to being engraved or rollstamped afterwards. Only the serial numbers are stamped into them.
The color of the anodizing was also a very light gray. So light in fact, that you could never find an upper to match so most people usually painted them black. The magazine catch fence is also very narrow compared to other manufactures out there. It's rumored that DPMS bought Essential Arms out as DPMS lowers resemble those of E.A. around the mag catch fence, or used to anyways. Need to comfirm this though.
Since it's a parts gun I'd give it a good going over to ascertain the quality of the parts it was built with. Back when E.A. was in business there were also a couple of third rate parts houses that advertised very inexpensive(read low quality, reject, or otherwise out of spec)AR parts kits that seemed like good deals to those on a budget or who otherwise had no clue. This along with some of these owners having little or no experience in building an AR led to many malfunctioning rifles. Anyway, not trying to scare you off just give it a close inspection. Even though it's a PreBan, don't pay a premium as you would for a Bushmaster, Eagle, PacWest, etc.
WpnsMan