In pre-wipe, when I had finesse, BB gun was my favourite weapon, because you like unarmed troll can come with it again and again, because you have 439857345 of them somewhere near, in TB you can easily make someone useless with it with 1-2 shots, in RT it depends on number of these guys, range of BB gun can't be more than range of mauser or 10mm pistol/smg, or else it'll be even better, I can remember crippling hands of Hawks or whatever else aPKs in NCR, where there were no guards, it was fun when I saw metal guys with miniguns/laser rifles running disarmed with crippled hands, till thier teammates doc them, if there was only 1 member, I could easily kill him with my BB gun, or atleast make him total invalid with both hands and legs crippled. Max. ammount of range that can be added is +1, so it'll have 25 range, equal to most pistols, so BB gun will be always worse than any other cripple gun, mostly because of +1 AP per shot in comparison to pistols.
About hunting "small critters" it whatever, you don't need a gun with sniper range to kill these harmless poor critters, I don't see any reason in this, plus if you're going to grind on these small poor critters, of couse they are usually melee, it means they will come to you anyway, and then you'll have almost point blank shots, atleast in RT, don't know about TB. Increasing range of BB gun will be good only in PvP, but.. well it's better to use AR/fal or alteast that crappy hunting rifle. The only good thing in BB gun is when you crippling someone's hand, then blinding and knocking him out, but his teammates killing you with rocketlauncher and minigun bursts and then you die, some metal guy running to your body with happiness and then after looting you, saying "wtf?? bb gun??".
If you want to use BB gun as protection against evil PKs with laser pistol (35 range) hoping to cripple his both hands while you're killing poor molerats, then you should take something... more expensive, because it's ok that laser pistol > bb gun, or run closer, or simply have deteriorated fully loaded AR/fal in 2nd hand in case of evil PKs appearing in your encounter.