I have had a number of things on my 40 cal JRC. Started with a Bushnell 3-9X40. Took that off and used a 2-7 LPD scope for a bit. Ditched that and used a cheezy NC Star compact 3-9 for a little while. These all worked OK but for whatever reason they got taken off. I also tried an aimpoint copy for a while, but even at 50 yds I can't see the target hits with no magnification. It currently has a Burris AR 536 (5X RDS, well more like a fixed 5X with a BDC style reticle really). It seems to have stayed there for a while and works for 50 and 100 yd ranges, which is pretty much the range of the gun without having to aim skyward to offset the bullet drop (just kidding about the skyward bit, but the drop is pretty significant.)
Like I said, I like lots of magnification, the 5X works OK for 50yds for me, YMMV. If you're mainly doing 50 yds and under the Burris AR336 might fit the bill. I also have a Sparc II on my CQ AR, but rarely gets shot over 25 yds, so no mag is just fine.
The JRC is one gun where I would not bother with the old adage of "paying as much for the glass as you do for the gun" = just not worth it given the limited range.
