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.

[Researcher]

Without a bunch of good pictures it doesn't exist.

[Notanexpert]

Here are a few. Let me know what else I can share that would be helpful

[Researcher]

I have seen 16-/20-gauge Remington Model 31s converted to 28-gauge, but this is certainly a first for me.

From the late 1890s the 28-gauge in North America was offered in the "standard" 2 1/2-inch shell and with a bit hotter load in an extra length 2 7/8-inch shell. In 1931 when the North American ammunition companies finally got around to applying a progressive burning smokeless powder, high velocity load, to the 28-gauge it was put up in the 2 7/8-inch shell. The first appearance of 2 3/4-inch 28-gauge shells came with skeet loads introduced circa 1939 --

SHUR SHOT 28-gauge, 2 3-4 inch, SKEET LOADS #9C, DuPont MX.png

Xpert 28-gauge, SKEET LOAD, 2 3-4 inch, $373, Aug 2019.jpg

RANGER 28-gauge, SKEET LOAD 2 3-4 inch.jpg

but 2 7/8-inch 28-gauge shells were still the norm until 1948/9 when the industry went to the 2 3/4-inch 28-gauge shell.

Back to your gun. It certainly appears to be a nicely done conversion. The rib doesn't look like the vent rib Remington used on the Model 11/Sportsman. What I can see of the matting on the rib it smacks of Moneymaker but the posts don't look like theirs. Remington normally placed the gauge and chamber length information on the left side of the barrel.

[Notanexpert]

Thank you for the insight Researcher, much appreciated. Couple more follow up questions.
1. Was it normal for custom converters to not mark their work in some fashion?
2. Do you feel the date stamp on the barrel of “SEPT 41” is an accurate date of conversion?

[Researcher]

From the old factory ledger your receiver was put in work during August of 1939, so the gun being converted to in September 1941 seems reasonable. Post WW-II the smallbore conversions I know of were done by Simmons, usually so marked and by Claude Purbaugh often not marked. I don't know who might have done this work before the war.

[Notanexpert]

Thank you. So if nothing else, this gun is the oldest known 28 g auto?