Trevor,
1st, welcome!
If he has the NRA Basic Pistol book from his class, it's on page 89.
Down and left (RIGHT HANDED SHOOTER):
"This pattern is caused when the shooter jerks the trigger, causing the front sight to dip low and to the left before the bullet leaves the barrel. To correct this type of error, the trigger must be slowly SQUEEZED until the shot fires, being careful while squeezing not to disturb the sight alignment and sight picture."
Left (8:30-9:30) page 90:
"This pattern is created when the shooter does not properly place the index finger on the trigger. In such cases, the shooter has a tendency to squeeze the trigger at an angle instead of straight to the rear."
My questions are:
1. what distance?
2. what group size?
3. resting on sandbags?
OP said bench rest shooting, so he may be getting as much of the human error out possible. Have someone else run a few rounds through it. I'm leaning more towards sights based on CONSISTENT TIGHT GROUPS. If you had a "shotgun" pattern, well then....
Went shooting today .22 rifle. My groups at 25yds are about 1 inch high and 1 to the right. Bench rest shooting smallest 5 shot group about the size of a pencil eraser. Hold 2 targets together see COMMON holes. Believe mine is a sight alignment. Or, I'm CONSISTENTLY doing the same thing wrong....
If you want someone else to test it, could give you a few names.