I own a couple hundred beater rifles and at the range I help other guys that cannot seem to sight in.
There are an infinite number of problems, but 50% of my problems and 50% of other shooter's problems have been loose scope mount screws.
Not scope ring screws, they almost never get loose.
In order to check mount screws, the scope must be removed, and what ever zero work had been done is lost.
I find that Loctite 242 on clean male and female threads makes for scope mount screws that never come loose.
Getting those female threads clean may not be easy. If the a barrel installed with grease, and the scope mount drill and tap in the receiver goes all the way through to the barrel threads, grease may want to ooze up through the mount hole.
Plan ahead, and use less grease. Clean the mount hole before screwing in the barrel.
For cylindrical bond, not thread locking, I use Loctite 601, as you can see in these pics of a VZ59 machine gun barrel I put on a Mosin Nagant. I made a sleeve from 1010 steel and bonded it to the outside of the barrel, so I would have a shoulder for the inner C ring of the receiver.
The word 'forum" does not mean "not criticizing books."
"Ad hominem fallacy" is not the same as point by point criticism of books. If you bought the book, and believe it all, it may FEEL like an ad hominem attack, but you might strive to accept other points of view may exist.
Are we a nation of competing ideas, or a nation of forced conformity of thought?