IIRC, the 300 was FWB's top model from about 1968 to 1972, falling between the 150 and 300S. Compared to the "S," most noticeable diffs are shallower stock fore end, longer barrel, longer cocking lever with hinged end, and non-movable trigger blade. There were a fair number of transitional guns that mixed action features, sometimes you have to look at the model number stamping to be sure.
The 300 was virtually un-challenged at high-level matches in its day. The "S" competed with the Anschutz 250, Diana 75, and Walther LGR over the years! My plain-Jane beech stock 300 is a hard shooter, VERY accurate, and the least pellet-picky of my FWB's.
Two bits that are vulnerable and now hard to find, are the plastic trigger blade (diff from either the 150 and 300S) and the hinged tip of the sidelever (use that only to unlatch the lever; grab the solid textured bit behind to finish the cocking stroke).
Trivia time: Tyrolean stocks were banned from UIT-sanctioned matches in the 70's, with demand then dropping off. But Dr. Beeman astutely bought up some FWB surplus (and their unique trigger guards). Many of the 300 and 300S Tyros in the US today were actually created in his shop.