1911A1 Receiver Marking

[roguetwelve12]

Greetings all!

Long time lurker, rare-actual poster... but I have a conundrum I simply can't solve.

I've finally worked up the nerve (and found the time) to disassemble my 1911/1911A1's to take a look at the markings within (receiver, slide, etc.). I've come across something I just can't seem to figure out.

For reference, this is a Colt manufactured 1911A1 SN 1676XXX. All external markings are correct and accurate per Clawson, and the slide is a wartime replacement (as evidenced by an "M1911A1 U.S. Army" stamping on the right side of said slide). It has the correct GHD Ordinance Inspector stamp on the left receiver just behind the triggerguard.

Upon taking the weapon apart, however, I am perplexed by the top of the receiver. As the picture shows, there is no ordinance maker stamp (which is correct as it was discontinued in mid-1942). However, where the Production Order stamp should be in the 4-5 O'clock position, there's a "B" stamp. (I apologize that the picture is so zoomed in, but I had to crop it that way).

I have absolutely no idea what this means! I had expected there to be a "G" stamp indicating a government order.

Does anybody know what this means/have any tips?

I thank you all very much for your time,

R12.

[roguetwelve12]

Also, I should have mentioned, Clawson doesn't mention anything about it!

[roguetwelve12]

Additionally, the barrel is marked "D" just anterior to the lugs (where's I've seen it traditionally be "F" or "7" or something similar). Barrel is otherwise correctly marked for a WW2 Colt production barrel in this SN range. Is there any insight as to what this might be?

Apologies for all of the questions. I really appreciate all of your insight.

Edit: Just figured out the answer to this, but the aforementioned question still stands in the original post! Thanks so much everybody!