Brownells a1 lower, I'd hole in back

BR7.62

Full Member
Full Member
Minuteman
Mar 6, 2017
314
140
43
blossburg pa 16912
I don't know what this hole is.
IMG_20180914_170037.jpg

Sorry for an unusual thread here but I'm not a member at arfcom to ask...
Goes all the way through.
 
Reproduction of early Colt AR-15 601 lower. Brownell's M16 repro doesn't have hole. Looks like for a roll pin - maybe a different buffer detent retainer?

Brownell's Gun Tech™ Note: The original Model 601 lower receiver was found on early AR-15 rifles produced by Colt Manufacturing from 1959 through 1963. These receivers were used on the first rifles issued to the Air Force - and those tested by the U.S. Army. The production numbers of original rifles with this type of receiver are quite low, making the BRN-601 an excellent base for a very unique "Retro" build.

Features of the Brownells BRN-601 lower receiver that make it a close replica of the original 601 include the front takedown lug profile and area surrounding the receiver extension.
 
ok i see that thank you!
that answers that then, i do find it weird that they dont all have it.
the other one of theirs i had was a blem w/ the markings on both sides, it didnt have it.
i was thinking maybe this was a blem of a different order.
thanks again
br-