The BT-17 is longer and all else being equal, more adjustment is always better imo. Plus, it will still fit using the spacing of the sling studs as home locations.
I just checked and I not only used the BT-17, but I did use button head screws. I suggest stainless if you can get them as the standard ones rusted on mine over two years of regular use.
Now here’s the kicker regarding use of the sling studs and the rail. You can’t, or shouldn’t anyway. If you mount the rail closer to the action and leave the sling studs, it’s really too close for proper use imo. You will have to do what I suggested above and remove the sling studs. Drill from the barrel channel for T-nuts and mount the rail using SS button head machine screws.
The Atlas rail has a flush cup for sling mount incorporated into it. If your sling only is for stud mount, you can easily purchase an adaptor to either leave on your sling end or leave in the rail.
The Flush Cup Stud Adapter adds function to push button swivel bases. Use the supplied allen wrench to depress the plunger and slide the stud into the base. The standard stud is ready to accept all swivel types and/or mounting of a bipod or accessories that require a sling swivel stud. Fits all...
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