Looking for info on an Enfield I just bought, I got it at an auction last week and thought I’d try to learn a little bit about these unique guns. I have this one with serial number showing: 20958 with a “U” to the upper left, and an “A” in the upper right. Any idea as to where I could find more info on this rifle? 

Thank you!

"U" may be either a letter prefix to the digits or mean "malleable cast Iron" is the material for the bolt head. "A" suffix usually means a non standard part, or parts fitted somewhere.

Cant tell you more without more info.

A lot going on here.  My input - to be checked by the experts:

The "2" in the serial number may mean it was manufactured at Royal Ordnance Factory (ROF) Fazakerley, which was a government owned factory.

The "A" as a prefix or suffix to the serial number means "Not readily interchangeable with other No.4 components"

The only real reference to the "U" is it usually appears on the SMLE Bolthead (British Production) and means "Metal composition specification, likely 'Unhardened' or 'Untempered' for cast iron content.  I don't think No4 are considered SMLE, but it appears common sense that the U may be applied with the same meaning.

All this comes from Skennerton's reference books.

Enjoy the rifle.

That position is about right for using a No1 Mk1 sight bracket for some kind of Aperture sight?

Its where the safety spring would be on one.

Unlike the bracket for a No1 MkIII which is like this. & can be fitted to a No4.

This "A" stamp is to inform Armourer's to be aware when repairing the rifle that standard spare parts may require some work to fit.

Yes, now we've seen its exact location it has nothing to do with bolt heads.

U20598 is the serial; number.

This is a much better description in plain english.  Thanks Zed!

Wow, thank you for all the info guys. I’m an avid gun collected/refinisher, but you guys have me beat as far as knowledge on these fine guns. The one on the left is a better picture of the entire rifle intact (it’s currently pulled apart as I am working on adding the safety, as well as refinishing the wood and overall cleaning it up). You can see that mid barrel, there is an aftermarket rear sight added in, however I’m not much of a fan on that one. This was advertised as a No4 Mk1 at auction, and the one on the right (obviously sporterized) was listed as a SHTLE III. As to the screw just forward of where the safety should be, removing that took out a piece that held the bolt from being released, which is contrary to what I’ve read as it’s usually the button just to the right of the bolt. My next goal after finishing this one up is to get one that is not sporterized, as I have come to respect these guns and their history as I’ve learned about them more and more. I’ll reassemble this weekend hopefully and can add a few more pictures.