Pretty much how I've done it for many years.
Never owned a bore sighting gizmo, but with bolt guns, just clamped the scoped rifle in my "gun cradle" and took it outside. Eye ball center the bore (bolt removed) on an object about 25 yards distant, then adjust crosshairs to align with what I see thru the bore. Not all that hard to center the bore via the eye.
For many years I took the gun and cradle out the basement door and sat them on the concrete cap on my stairway wall, which was about 4' above the floor. Had my old Ford tractor parked out back, roughly 25 to 30 yards from the house, so I used one of the headlights for the bore alignment process.
Had done that dozens of times for my own rifles and those of others, for whom I had mounted a scope. Took rifle to range, set it up on the 25 yard bench and proceded to make final adjustments.
Have done that in as few as two shots, max probably about 4 or 5? Oddly enough, once mounted a scope on my 444 Marlin (no bore sighting) and when I fired it @ 25 yards, it was almost dead on. Hadda been dumb luck?
I tend to let mine dead on @ 25 yards for elevation, then move to the 100 yard bench and adjust for final elevation zero. Sometimes the windage set @ 25 will need a minor tweak for 100 yards, but it usually doesn't.
Watched a guy do that once and apparently he had cranked his elevation higher after the 25 yard zero, because he couldn't hit the paper at 100 (IIRC, a roughly 8.5x11 target from a pad?) I spotted for him, discovered that his rifle was about 6" or more high at 100 and was hitting just above the top of the target, with a dead-on center hold.
Most centerfire rifles from 223 to say, 270, will generally hit within an inch or so of center of target aim at 100, with that 25 yard "zero".
If I've mounted a scope with finger adjustable elevation turret, usually zero it at 100 and reset the turret graduations to zero.
Otherwise, depending on the rifle/cartridge, may "zero" it high at 100, with calculations for being "dead on" at say, 300 yards if a varmint rifle? One of my old 22-250s has been that way for many years and has popped a mess of woodchucks, some out beyond 400 yards.
And yes, I have seen guys leave the gun shop on the Sunday evening prior to deer season, with a new rifle and bore-sighted scope. Always wondered how that worked for 'em the next morning?