I just purchased a Mossberg 590SP shotgun. I thought I’d slap a sidesaddle shotshell carrier on the reciever, one that mounts with screws(Mesa/Tac-star)as opposed to adhesives.
However the Mossberg reciever is aluminum, and I have heard that some feel that this is a bad idea with such a reciever. Is there truth to this, or is it no worry? 
I have a mesa on my benelli m1, no issues. Loctite is your friend, just dial it in as tight as you can get the mount without binding the bolt in the receiver by hand cylcling the action.
FWIW, I added a strip of carpet tape to keep the front tabs of the Mesa in place, but the benelli mount may differ from yours.
No worry’s.
I’ve had a side saddle on my 500 for over 15 years now. Rezarf2 is right on. Dial it it so it doesn’t bind the action and lock-tite the screws. It’s not a part you’re going to be taking on and off very frequently.
I’ve had sidesaddles on 590s for over a decade without any problems. Pump guns are a little less succeptible to problems with pinched recievers, as long as you aren’t hogging it down.
On the TacStar, use blue LocTite. Tighten the shell carrier screws down to the point that the plastic slightly bulges, and use LocTite on the ejector replacement screw so that it doesn’t get loose and jam your bolt up. Tighten the trigger pin replacement, but you shouldn’t need to overtighten it. With the LocTite it should be fine. You may want to use some witness marks on it so you will be able to see if it is backing out.
Speaking of that ejector replacement screw and the TacStar, they included a little nut to go on the screw, from the backside of the plate, it’s virtually impossible to tighten.
How tight should that nut be? I can only basically finger tighten it.
A nut driver works or grabbing the nut with a pair of neddle nose pliers.
I ended up using a nut driver…
That is what I used as well.
The newer Mesa Tactical sidesaddles have a Chicago screw where there are two heads and the shafts thread into each other. You can’t screw them to the point where they torque the receiver. If you get an older one with the old bolt and nut, you can call Mitch at Mesa Tactical and he will send you the newer hardware.
That’s good to know… Thank You 