I had my hornet converted to k-hornet for just that reason, the goal was to extend the usable range for coyotes (usable to me is 400 or so ft/lbs of striking energy). Your typical hornet load runs out between 100 - 125 maybe a little more. With the the better BC's and extra weight on paper my k-hornet should be good for close to 200 yards. At this point I have only used it on gophers and there seems to be ample expansion with Sierra blitz bullets. I did do some gell testing and while there was ample ion there did seem to be limited fragmentation.
Here is the kicker this year (after I had had the conversion done) hodgdon published data for the hornet lil'gun and a 50 grain head and it is only about 100 fps slower(2700 fps, previous data was more like 2400) I don't know what the min velocity is for a v-max but I do belive that for Nosler bt's it is 1600 and I think the v-max is a softer bullet. When I ran the numbers for my k-hornt I did not cross 2000 fps till just after 200 yards so while at the bottom end of the envelope there is still plenty of room.
So the short answer is yes you can use a 50 gr bullet the rifle has the twist to do it and lil'gun should give you enough velocity to be useful. The best hard to say, if I was just shooting gophers then no the lighter more fragile bullets would be better. And for coyotes time will tell this is the first winter it will be used and we will see how close paper and practical are.