Luckily you have a Sentry as they are great at providing the missing combination. However, you have to prove your safe ownership to Sentry using the steps below in order to get the combination - there is no work around to this. If you contact a locksmith to open, they would be the ones verifying your safe ownership and could get it quicker for you but without a locksmith handling this as a middle man, the notary form directions below are the quickest (and most cost effective) means to get your master combination.
Unfortunately, Sentry safes do not have a skeleton combination that works on all safes or a way to reset to any type of "default" combination. In order to open the safe, the master combination is going to need to be used. There is not an override code for a Sentry Safe and you must get the original master combination in order to open the safe.
Here are the directions to get your combination from Sentry. These steps are needed in order to prove your identity and ownership of the safe. You would not want someone to steal your safe and then just provide the serial number and model number over the Internet (both on the outside of the safe) and be able to gain entry to it. Sentry has these requirements for everyone but they have good customer service for their customers.
You will need to click on the "Download Notary Form" there on the page - download and fill out all the information on that form and have it notarized (this is proving your identity for Sentry). You then mail or fax that sheet to Sentry at the provided location.
You can also directly download the needed notary form here:http://www.sentrysafe.com/pdfs/NotaryForm.pdf
Within a few days after they receive the notarized form, you will receive the combination.Unfortunately, this is the only method that Sentry allows in retrieving combinations. If you need further followup, please hit reply.
I highly recommend once you get the combination to go on sentrysafe.com and register your safe. In that way, if you ever forget your combination again, you can just log in and instantly retrieve it from the site.
If you need any followup, just hit Reply to Expert (do not rate)... I deal with Sentry regularly on these issues and you should not have any troubles - the main thing is to get the form notarized by a notary with a different last name than your own to prove ownership.
Have a wonderful week and all the best to you.