Pretty useless. Just take the bolt out look down the bore at a distant object make the scope or sights line up with the image you see in the bore then your ready for paper at 50-100 yards.
Thats how bore sighting is actually done.
The only guns that dont bore sight well regardless of method are garands m1a ruger 1022 and such. For those types just start at 25 yards and only adjust till your on paper if your hitting paper back it out to 50 and go out to 100 after that. Do not make any adjustment unless your off paper or you can easily way over correct.
Your 25 and 50 yard shots should tell you which way your shots are going off so you can adjust at 100.
No need at all for a "bore sighter" of any sort.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...