There are three bottlings of Old Grand-Dad Bourbon: the 86 proof, the 100 proof (bottled in bond), and the 114 proof. My understanding is that the Bourbon in these three bottlings differs only in proof and that the three different proofs are all bottled at the same time one after the other (ie, they dump the barrels going into a particular batch, dilute the result to 114 proof, bottle as much of that as they need, dilute the remainder to 100 proof, bottle as much of that as they need, then dilute the rest to 86 proof and bottle it). When it was originally conceived (probably back in the '70s), the 114 proof was probably around the proof that the Bourbon came out of the barrels, but it's unlikely that this is the case anymore. It's typical nowadays for Bourbon to go into the barrel close to the legal limit of 125 proof; and Bourbon, unlike Scotch, tends to rise in proof with age.
Surprisingly enough, there actually was an Old Grand-Dad. The brand has its roots in the whiskey distilled by Raymond B. Hayden in the 1840s. He needed something to call it, so he named it after his grandfather, Basil Hayden, one of the proto-distillers in Kentucky at the turn of the 19th Century. It managed to survive Prohibition, and Jim Beam bought it in the late '80s. Typically, when Beam bought a Bourbon brand, it would just take the label and the distribution and bottle it out of stock distilled using Jim Beam's standard mashbill and aged in Jim Beam rickhouses. With Old Grand-Dad, Beam also took the mashbill, and it distills OGD using that mashbill and barrels and bottles it separately. That mashbill is very rye-heavy, one of the most rye-heavy of any Bourbons.
When first poured, this Bourbon smells very, very fruity. I'm not sure if that's the rye or the high proof. With time, the fruitiness tones down a bit. Eventually, it develops a bit of vanilla, but the chief aroma is cinnamon. The taste is also dominated by cinnamon, and there's a good deal of burn (as there ought to be for a 114 proof spirit). I like it, but I wish it weren't so high-proof. After this bottle is finished, I'll probably try the 100 proof Bottled in Bond.