1941 Model 11 Sportsman 28 gauge?

[Notanexpert]

I have a Model 11 Sportsman 28 g in my possession. The serial number and other identifying info would state this gun is a 20 g. The barrel however is a true 28 g barrel. It is stamped “28 GA 2 3/4 SHELL”. On the bottom of the barrel it is stamped “Sept 41” with a 3 digit number “109”. The date stamp of “Sept 41” falls in the timeline of the serial number 1055929. The barrel fits perfectly, it has a vented rib with solid posts. It has not been sleeved or stamped over. The bluing on the receiver matches the barrel. I have had the gun for roughly 40 years and it shoots and cycles flawlessly. It had a 410 match as a skeet set but I wasn’t able to get that gun at the time. This has been a mystery.
1. Could this gun have been some sort of prototype that got put on hold because of the war?
2. Could this gun have been a boutique conversion by some high end gun smith? If so why wouldn’t they have put any identifying markers on the barrel?
3. Could this gun have been made by a Remington employee as a personal gun?
I have pics and will try to upload them. Previous attempts have failed. Curious what other thoughts out there might be as an auto loader Morel 11 28 gauge from 1941 isn’t supposed to exist.

[Notanexpert]

Here are some pics. There is another thread I accidentally started on here too so there’s been some comments on those along with pics. I can upload any other pics that might be helpful for anyone with more knowledge than me.