Phil,

Your terminology is off a bit.  What you are referring to is simply the “pistol grip” type.  A grip “cap” is a non wood piece that is installed over the end of the pistol grip, usually black hard rubber (with the Winchester logo embossed in it).

Nearly all of the early production standard Model 1897 shotguns were made with the “round knob” style pistol grip (as shown in your second picture).  There were a very small number that were “English” straight grip style stocks (no pistol grip), and most of the Trap Guns were made with the English straight grip stocks.  The relatively rare Pigeon grade guns were sometimes equipped with a true capped pistol grip.

Beginning in late 1906, Winchester began phasing out the round knob pistol grip stocks with the “semi pistol grip” (as shown in your first picture).  The round knob stock was an optional stock through 1913 when it was completely discontinued.  The semi pistol grip stock was used through the end of production, though in later years (and I am unsure exactly when), the pistol grip area was fuller (thicker), and slightly more pronounced than the earlier production semi pistol grip stocks.  Additionally, the later production stocks are found with a fluted comb.

None of the WW I Riot or Trench Guns were equipped with the round knob pistol grip stock, which is why Joe Poyer made no reference to them.  Only the early commercial production Riot Guns had them.  I personally really like the round knob stocks much more than the later semi pistol grip.

This is what a really nice condition early Riot Gun should look like…

Bert