Type of rib: compensating with round rib posts
or solid rib with rectangular rib posts
Rib inlays: gold, silver or none near the breech
Type of stock: pistol, half pistol or straight
Shape of forend escutheon: banjo or rectangular
2-56 Screw: presence or absence of small non-
slotted end of screw near the forward right
side of trigger guard on trigger plate.
We have never inspected or documented a Whippet grade SBT gun although, according to LCSCA records, twelve were made and shipped to known destinations. The same is true for five Ideal grade SBT guns. We also have never documented a SBT gun with a Whitworth or Damacus barrel but are hesitant to say they don't exist.
The LC Smith ventilated rib first appeared on SBT guns in 1917 in the form of compensating ribs. They were changed to solid type ribs in late 1919. The first ventilated ribs appearing on double barrel guns was in 1925; there has never been a documented compensating rib reported on a double gun and it appears unlikely they were ever fitted with such since they were dropped six years before.
But in this business we never say "never" or "always"!
If you want to read more about SBT guns look under "Grades" on this site.