Is this the 300mm f/4.5 AI Nikkor-H lens? (This lens was produced from the late 60's to early 80's.) If so, according to Bjorn Rorslett (http://www.naturfotograf.com/index2.html) it is mechanically excellent but optically not as great. He rates early versions as 2 out of 5 and late versions as 3 out of 5. For comparison, he rates the f/4.5 AI ED version as 4-4.5 on an FX camera and 5 on a DX camera.
That being said, good long lens technique along with an aperture around f/8 should result in good images.