When I was shooting on several Marine Corps rifle teams, the Corps issued me a 20X, 40mm objective lens Baush and Loamb . With it I could spot thirty caliber holes at 300 yards. Laying next to the shooter I could spot the break of his bullet out to 300 yards.
It's not the power of the scope, unless you buy under 20X, that allows you to see 300 yard bulllet hole, it's the resolution. If I were buying a scope it would be a variable in the 15X to 50X range.
There is a problem with high magnification: on hot summer days it's difficult to see thorugh the mirage using high magnafication. A variable allows you to drop down in power and to be able manage the mirage.
Most cheap scopes lack resolution. Buy what you can afford.
Clifford L. Hughes