Howdy guys, I picked up a grab bag of AR muzzle devices over the weekend and was just going through them this morning, normal run of the mill A2's and such, but there is a Duck Bill in this mess as well,  I own a couple of early guns with Duck Bills on them, but doing some searching this morning have not been able to find a definitive answer on what all of the models the Duck Bill actually came on?

This one is in good shape, I don't believe it is an original as it has a concave on the bottom that would match with the current crush washer.

Just gathering more information to put in my notes, I seriously doubt I will build a reproduction early model, but figured it would be nice to know all the models it was used on.

Thanks.

Poke around on here. Lots of useful info. http://retroblackrifle.com/

The short answer is that the duckbill was only present on very early 601s, later replaced by the improved 3-prong, which was also used on the 602.

Early transitional 604s (XM16E1) could have had either the improved 3-prong or standard A1.

Are you sure it's a duckbill and not an improved 3-prong?

ETA: That should read "early transitional 603s" above. Not sure if the AF 604s ever had 3-prongs.

Circuits,

You are probably right, it looks like it is probably the improved 3 prong, in looking at the link the poster above you provided.  I looks like the improved one.

Actually, duckbills came on 601s till the end--or at least near the end of the production run.  I've seen unmolested rifles in the 12k+ serial number range with duckbills.
Without going through all of my old notes, I believe the mag button with horizontal grooves was the first "iconic" Model 01 component to expire, switching to the many circles button very early in the run.  Then the Type A stock gave way to the B decidely past mid-run.  Then the 1-14 barrels changed to 1-12 quite late in the run.  But as far as I know, the duckbill made it all the way to the end of the run.  (Disclosure: I have not found a truly late, as in 14k+, 601 in original condition.  But if any did come with the improved 3-prong, that change came very late.)

TBR says the improved 3 prong was introduced on the 602. I've never seen anything to contradict that.