I own a Sturdy safe that is equipped with a Sargent & Greenleaf combination lock. I've had the safe for about 2 years and in the recent months, the lock refused to open even when the correct combination was entered. Usually after 10 or so tries, it opens. So I got on the phone with a tech from Sturdy safes and found out the issue and how to fix it.
When the door is closed and the handle is dropped to the close position, the bolts on the door slide out and locks against the frame of the safe. When the bolts slide closed, a tightly fitting door will cause one or more of the bolts to rub fairly hard against the metal of the frame. This rubbing can cause the bolts to stop before it's fully engaged. We're talking about a tiny amount here. In extreme cases, metal is pushed and creates a tiny nub that prevents the bolts from extending fully. This condition creates undue pressure on the lock mechanism that can cause the tumblers to go out of alignment, in my case, by one number. (So out of the 3 numbers, the middle number was off by 1.).
I fixed this by sanding smooth the contact point between the bolt and the frame and cleaning the bolt surface with a clean rag and some rubbing alcohol. So far, it seem ok and I no longer have the problem. I'm sure a lot of safes out there use Sargent & Greenleaf locks and have similar designs so I hope this helps. Apparantly this is common enough that the tech was aware of the problem and the quick fix.