I have three dedicated spotters but 99% of the time I try to use the spotters I am already carrying on my rifles/carbines.
At 500yds with white paper, my burris xtr2 3-15x scr-mil and 5-25x can see 5.56 holes in white paper and so I'm sure they can see .22lr holes in white paper at 300yds.
If you use "easy-see" stick on dots ... or even regular colored dots on the white paper for aiming points, then you should even be able to see the holes in the dots.
It is hard to see black holes in the black circles on the nra paper targets at longer distances.
I have a tangent theta on my wish list ... might be the best "spotter on the rifle" I can afford ... resolution !!!
Plus if you use the spotter on your rifle, you don't have to spend time switching back and forth to the dedicated spotter to look for the holes. You saw the hole appear in the target already !