Looks like a REDFIELD JUNIOR base or a copy of one. VERY solid bases which were developed by a WW1 sniper who as trying to build a better sniping rifle. He succeeded.
Normally, they are no trouble at all to remove: just unscrew the Ring, then undo the three (or possibly four) screws holding the Base to the receiver of the rifle and lift the Mount free.
If you don't want crap and crud getting into the holes where it was D&Td, put in a set of PLUG SCREWS and it will take a very close inspection to determine of the thing actually has been D&Td at all.
The PROBLEM arises when the Mount is attached to the Rifle. People do NOT want the screws working loose, so they use RED LOCTITE or some similar thread-locking compound to keep the screws from vibrating loose. BLUE Loctite is what a professional shop would use: it locks up very solid and will NOT vibrate loose, and you can take the thing apart with a solid grip on a screwdriver.
The Problem is when guys use RED Loctite, which is meant to go on and STAY on..... permanently. RED Locite CAN be removed, but the job requires HEAT.... and you do NOT want to go heating up that beautiful Receiver and wrecking it.
So you do the logical thing and grind a screwdriver to FIT those Screws. THEN you HEAT THE SCREWDRIVER and put it into the screw-slot right away. The Screwdriver Shaft will hold the heat and the Heat will TRANSFER to the Loctite which is HOLDING the Screw tight. You then break the screw loose with the Screwdriver and repeat as necessary for each Screw. The Screwdriver then will be toast, all the heat-treatment completely wrecked, so you mark it and put it to one side and use it for this type of job only.
And if you ever decide to find out just HOW accurate these rifles were (and I can say that they could be quite astonishingly accurate), you can slap the Redfield back on, add a GOOD scope and head for the range.
Hmmmm........ seems to me that Redfield also makes very good scopes. They are not $29.95 but they ARE good optics and SOLID.
Hope this helps.