Remington Model 33

[Driftless16]

I recently picked up a Model 33 single shot. It's my first older gun I've purchased and was looking for when it was made. After some research I see that the Model 33's were made between 1932 and 1935, give or take a year or two based on what different people say. I see on the side of the barrel it's stamped "ED", which leads me to believe my rifle was built in September of 1935. But, right above the "ED" there is a stamp of the letter "U". I can't find anywhere what this might indicate. Can anyone help me decipher this stamp? Another stamp that I noticed, but I'm not too interested in, is on the opposite side of the barrel there is a stamp "78". Can I get any help with this too? Or can anyone point me in a direction to figure this out?