I have looked at guides and photos, but I can't really see the difference unless it is the slight angle on the underside?

For example, what is this stock I am refinishing? (pic below).

I couldn't understand how long the C type was used, or if it was used concurrently with the D?

Thanks.



I'm "stocking up" for future needs. ;)

There is much information, thoug it probably is in the archives now. The easiest way is to look at the surfaces that contact the receiver, which your pics don't show. The single biggest givaway is that there is no straw hole on a "D". Strawhole is where the foam can be seen through about a 1/4" hole that is in the center of the "boss" that engages the recess in the rear of the receiver..........keeps the stock from turning on the buffer tube. The "C"'s don't have that 1/4" hole. THIS ISN'T ABSOLUTE...I'll take a wild guess and say it is 99.9% accurate.......there are and have been exceptions to this "rule"
 Also, the wall thinkness around the buffer tube hole, when viewed looking straight-on to the hole is much thinner than on a "D".  There are pics around, you'll just have to search.   hth

Stocks

There is a slight difference in the external "crease" (bend) between the C and D, but the easiest way to identify them is by looking at the front end (the part that contacts the receiver).  Early C's had no "strawhole," but later C's did.  The consistent factor, though, is that the wall thickness of all Cs is noticeably thinner than the D's.

Some photos and measurements are here.
Once you've looked at a few C's in person, they become very easy to detect.

Thank you, that helps. One of these had the 'straw hole' through the locating tab.  I saw it but did not know what it meant.

Also the one I pictured had unique contour near the tab; It did not match the E type stocks I knew.

I have been shooting AR's since '75 but this older detail is new to me; and I like to know detail.

Check you're stocks before you build. . I had what I thought was a standard type D, nothing
Special but it was in great shape.  I had set it aside to experiment with a fiberglass weave , I figured
I would destroy it in the process. .

When I started sanding it I hit what I thought was grey primer,
Went through that I found brown. With some forum help it turned out I had a
Type B !  

So every stock I get now I sand a little out from indeed
The hole for the extension,,, you never know.
My 20$ stock turned out to be worth. 250$!!

C stocks are a lot more expensive.