Yes the rings with a rail do work. That is a lot better than the double ended plastic clamp that some vendors sell.
If he has a rail on his hand guard (top, sides, or bottom) he can mount the light on the rail also.
On the top rail use an offset mount, lots of options for rail mounting.
Some vendors sell an windage/elevation adjustable mount but if the pill is properly centered in the light he should not need that.
