Question on newly-acquired 1943 Remington Model 11 military shotgun

I recently acquired a Remington Model 11 military shotgun with all of the correct markings and dimensions. What has me puzzled is the date code on the barrel. By all accounts, the AM means it (the barrel) was manufactured in March 1921 or 1965. That doesn't make sense to me since the SN of the receiver 480xxx puts it solidly during 1940's wartime production. Any theories on the odd barrel date code? I've seen one other AM date on this model shotgun, it was on the RIA site a while back. Thanks much in advance for your help.

Nice looking shotgun...

I've seen several with the single M date code. Maybe these were marked in error that way or who knows what happened. But I wouldn't be too concerned about it, particularly if the barrel serial number matches the receiver number.

I haven't taken the shotgun down yet, the forend magazine cap is pretty tight. I assume the SN is concealed somewhere when the shotgun is assembled? I have a Model 11 "meat gun" in 16ga so I am familiar with the disassembly, friction ring settings, etc so taking it down will be cake. Thanks for the insight, I wasn't aware the barrel was SN matched to the receiver.

For those like me who weren't overly-familiar with the type: Browning Auto-5 - Wikipedia Quite a story.

The barrel serial number is on the barrel takedown lug. Once you take the barrel off you will see it.

Yep, it's matchy matchy. Very very happy with it. I'd love to know more about the mystery barrel date codes but hey that's part of the fun in collecting.