I don't own a GSR, but do own a M1A-A1 Bush rifle, and an 18.5in bbl M14S.
After trying on the FWD mounted scopes ( SAI scout mount and M8 ultimak rail), I found that both types just weren't for me.
It adds weight up towards the front end, and destroyed the overall balance that this type of rifle has........for me at least. Limited options for optics as well as NVS.
I went back to the ARMS 18 (older split rail type) receiver mount and haven't looked back since. (Already had one mounted on the M14S).
I messed around with a few different optics, and am evaluating a Leupold VX-1 1-4x20mm scope as of late.
Good points so far:
1. The scope is rather light in weight as well as compact, so it doesn't interfere all that much in the way of additional weight, or overall balance of the rifle.
2. The scope sits rather low in relation to the receiver, and is what my goal was from the outset, as I don't like to use raised combs for cheekweld.
3. Plenty of eye relief.
4. Reasonably priced.
5. Very reliable so far and no issues with using it in rain or snow.
Not so good points:
1. I have had better quality glass on rifles like this before, but not at the same price I paid for this scope. Still, I wish it had a bit more clarity at early morning/late in the evening .
2. 4x is pushing the limits of where my own MER with this rifle is. A 6x might prove to be a tad bit better, but at the cost of more weight. Still looking at another option. ( I might set up the other rifle with a bigger optic with adjustable comb, but haent made up my mind as of yet.)
Note: My goal for this was aimed at ending up with a reliable, "Utility/general purpose", semiautomatic rifle that had to accomplish a wide range of shooting and hunting situations, so this route proved the better way to achieve this in my case.........as compared to the "Scout" concept.
Good luck with your search.