How do you ID the manufacturer of an unmarked aluminum stock? I picked this up because it is aluminum, but I have no idea who made it. Any help will be appreciated.

Colt's are usually marked under the latch on the body.  Usually the number 1, 2 and NN in a box or some variation of that.  Sometimes the latch is marked Newton.

The next one you'll see a lot of are B marked on the side.  Usually small and raised but sometimes larger.  Those are bushmaster stock bodies.  Not sure how but Essential Arms used those as well to make their stocks.  Maybe Bushmaster didn't own the die.

There are a few unmarked ones too but usually the commercial spec or waffle pattern on the butt end will give it away that it's not a Colt.

There were some really rough ones too with had a number in the side, rumored to be Nesard.

Got a pic of the pattern on the buttpad?

I will add one. Thanks. This one seems like a rough casting, but I have looked all over it and there are no markings.

i had some similar to that.  i got them as raw unfinished castings and a member helped clean them up, fit them and get them powdercoated.  they weren't the prettiest and the waffle pattern on yours looked similar to mine.  i never did find out where mine came from or who sold them.

here's the buttpad of the ones i had finished out


the more i look at yours, they look like the ones i had.  down to the rough sanding marks on the latch and washed out details on the buttpad.

here's an old thread of mine with some pics:

http://www.ar15.com/archive/topic.html?b=3&f=123&t=510390

Yeah, that pic of yours looks identical to mine.

A few red flags for it not being Colt.  Hard to explain in words.  You have to handle a bunch of these to get what I mean.

Mainly the diamond plate tread looks like it's at an angle. Thats odd.