Stoeger XM1 ranger

Been shooting my xm1 ranger for about a week now still breaking it in and seeing what it likes to eat but have a question. if anyone has ether the ranger or scout what do yall use to tighten the tension nut at the end of the barrel/shroud. when I first got mine it was completely apart in the box so I just snugged it up by hand but it wont stay tight and there's only 2 little notches to get something there to tighten it. any help would be appreciated. love the ranger its great been very consistent in 22 getting right at 65 shots before it falls off the reg
 
At our shop we keep some virgin Dzus tab screwdrivers on hand to modify if and when we get a gun that needs a special size. These are just two I took a quick pic of.

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