Dear Jerry,
Holland believes the bullet glanced the mast arm sufficiently hard to cause it to lose its copper jacket, thereby explaining why the bullet smear found on the curb by Tague had no copper in it.
Holland also says that a possible reason the hypothesized glancing "dent" on the mast arm couldn't be found some fifty years later was because the mast arm had been repainted five times (iirc) since the assassination, and those coats of sloppily-applied paint had filled in the dent sufficiently as to make it undetectable.
-- MWT 
Actually it was found the underside of the mast arm had the thickest layers of repaint. The upper surface had minimal paint and some areas were showing rust. It was quite easy to see if there existed a dent.
"The surface examination and processing revealed no
obvious features that could be attributed to a bullet impact."
-- A Technical Investigation Pertaining to the
First Shot Fired in the JFK Assassination
(Holland & DeJonja, 2016)
A shot causing minimal damage to
mast arm would not deflect much.
| | 
Amount of deflection needed to
make Holland's theory work. |
