By the time you get snap shot mages aren't too likely to fail concentration checks. I guess on NPC WBL it's a maybe, but there's also the problem that you're not at all mobile and getting up close to a mage is hard for you. Signature deed requires 11 levels in gunslinger which you don't have at character level 13 in the above plan, and you need to select a deed for it to work with too. If the mage turns invisible you lose, if they fly or run 125'+ away you lose.
So: mobility and ability to deal with invisibility/darkness/fog, and some way to hamper a mages ability to cast spells, on a gun-wielder. Good saves would be nice too.
A barbarian can have surprisingly good senses and moves a little faster than average, a savage technologist barbarian has a solid reason to use a firearm, readying attacks against the enemy mage to interrupt spellcasting isn't a terrible idea. It's a plan.
For the rage powers you want ultimate clarity ASAP. You'll need a one-level dip in something if you want a free gun of course. Your feats will be aimed at overwatch style or vital strike; not both. If you want to use the sword and gun ability of the savage tech you'll
want to be a tiefling with a prehensile tail or similaruse a cestus and a pistol; it's not required that you use that ability though. Saves may be a problem, true, but after 6th level you may have rage powers free to help.
Thank you for your help.I wasn't aware of the level requierment for siganture deed.
I'll have a look at your suggestion and will adjust my charakter accordingly.