I shoot both 50gr & 40gr out of my AR.
I shoot a RRA coyote with 20" barrel.
While the 50gr do a real nice job at the range, the 40gr do
a little better. So, I use the 40gr when I want super tight
groups but I use the 50gr when out hunting.
Really not that much difference in the grouping but I'm kind
of anal about it. We're talking 1/4" or less difference in
group size and both are well under 1" at 100 yards.