Originally Posted By Wangstang:
I seem to recall a thread that wasn't from all to long ago which showed various revisions of the bolt hold open design and there were questions raised about why the changes were made.

My searches haven't turned out that thread but another member's post triggered my memory of the thread.

Another member posted a PDF to this report:

http://www.ar15.com/forums/t_3_123/671533_XM16E1_Barrel_Erosion_Study_1966_on_PDF.html

While reading the report over, I found this information:



It's was an interesting piece of information from the report and I suspect it helps explain why there were some notable revisions to the design in the early years.

Wes

Originally Posted By PrivateSnafu:
Greetings all. Been busy researching bolt catches that came off of de-mills.
Here is what I've found. There appears to be six types or variations of bolt catches. Please review the detailed photo comparisons of the six type of bolt catches that was used.

Sorry I was unable to have all six types in one photo. But you can figure it out.

Tell me what you think.
The type 2 transitional is also randomly used in thee and four digit SP1s and seems to have been used around 1964. And they are not Colt marked, but simply have a forge number with out the C.
Hopefully WpnsMan can add to the dating and info.
Dave
















#3 has the separated follower lifter arm(with under cut) and bolt catch stop and a forge number. #4 has the follower lifter arm and bolt catch stop molded as one and has no forge number.