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looks like a torx
Don't use cheap tools, you will regret it.
Hollow ground screwdrivers.
That actually looks like a Torx+. There is a big difference. Don't use a Torx in a Torx+ fastener. You might get away with it or you may strip it out. Brownells has a full line of gunsmithing tools. If you need to borrow one I'm in Townsend.
View attachment 182774
This is a Torx+ fastener. The lobes are rounded. The standard Torx have a more pointed pattern. From the photo it could go either way. I've seen all kinds of Torx+ stuff showing up in all kinds of places. I just bought a complete set of new bits to deal with the influx.
Looks like a torx screw to me, too. I would recommend a set of punches and a rubber mallet, along with a set of hex keys as well. Probably want a torx key to fit the screws in your scope rings in that pic as well.
And get some purple Locktite so it won't walk loose again. Don't use blue or red on it!
Thank you for the links. Pretty much what I wanted.
While you are at it, you should get a torque wrench if you are going to be mounting scopes. Wheeler makes a decent entry level tool that comes with a set of bits that should be all you need for this job.