To open a sentry safe with combination you can follow the below steps.
Sentry safe locked with door open.
Pull the handle on the safe down within 4 seconds of typing in the code.
It should be noted that this kind of sentry safe is designed specifically to protect against fire damage not burglars with rare earth magnets in socks.
When you enter the code and the light turns green grab the handle next to the keypad and rotate it downward so the bolts come undone.
The lock must have jammed.
You could try a little graphite into the mechanics of the bolts to see if you can free them.
What can sometimes happen if locked when the door is open is that the rods are able to travel a lot further than they do normally and can get stuck.
Try looking for a small plastic button on the hinge side of the door push it in after the combo it is a deadlock type of feature.
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Other safes including most gun safes on.