OK, it MAY have been a factory front sight (maybe for a M77 even) at some point, but it has certainly been altered, and I'd bet it was added to the plain barrel of this rifle; just as the original plain quarter-rib was replaced with a 1S rib with the sight slot.
With 22-250 being 100-400 yard varmint round, I am completely surprised to learn that anyone would mount iron sights on a rifle in 22-250. I have owned three different Ruger Varmint rifles, a 1V in 220 Swift, an M77 in 204 Ruger and a 1A in 222 Remington. Just having the No. 1 in 222 Rem as a 1A seems like a mistake to me, so I sent it off to be reconfigured as a 1V (still in 222 Rem.).
To get the best from 22-250 (or any other long range varmint cartridge) in any rifle, a decent scope seems to be a no-brainer.
1. When I had the 1V in 220 Swift, I mounted a variety of scopes, finally settling on a Nikon Monarch 8-32X50 ED. With that scope on that rifle, 1/2 MOA at 200 yards was pretty much standard results.
2. My Ruger M77 Hawkeye in 204 Ruger sports a Nikon 6-18X40 Buckmaster. I spent last Wednesday shooting that rifle at various distances, ending the day punching holes in tomato can lids and similar small targets at 300+ yards.
3. When my Ruger No. 1A in 222 Rem gets back from being converted to a 1V, I expect to seldom shoot it at less than 200 yards, so I will be mounting a recently purchased Weaver XR T-36 to it.
Once I compare the long range results of the 1V in 222 Rem to the M77 Hawkeye in 204 Ruger, I may trade scopes between the two. I certainly would never mount iron sights to any of those rifles. It would waste the long range potential of the cartridges. Even my Savage 93GL in 22 WMR has a scope. It is an old Redfield 1.75-5X Wideview. I like to see what I am shooting at.