Here's the rationale for my suggestion and a few things to consider:
1. Realism - Bozar in 2238 is a sniping system, while Big Guns are all bullet/flame hoses with the exception of bazooka (which is a different class in itself, but doesn't really fit elsewhere). Obviously, sniping requires a different set of skills than firing an automatic weapon, so it makes sense to put Bozar in a category which includes other gunpowder operated (ie. having recoil) precision rifles like sniper rifle, hunting rifle and assault rifle. All in all I think that anyone with a bit of firearms experience would agree that the way a weapon is operated should be more important than the overall weight when it comes to classification in RPG terms.
2. Fallout 2 faithfulness - I admit that's the weakest link because, well, the Bozar in-game was a big gun and I've no idea whether the original sniper-Bozar concept was a big gun or not. It'd be nice if someone could clarify that if such information exists and is proven.
3. Balance. Basically, Small Guns have no immediate punch on mid to long distances. That doesn't mean they're worthless, it means that they mostly maim, incapacitate or knock out instead of killing the target. They're also arguably the weakest of all three weapon cathegories when it comes to plain damage output. Bozar as a Small Gun would somewhat fill this hole - and making its range slightly smaller than that of a Sniper Rifle (I'd say 40 or 45) would bring some diversity by giving the people an option to choose between range and damage, making for some interesting tactical variations. To make this powerful gun somewhat elite and keep it from becoming overused it could run on 7.62mm ammo, which isn't easily craftable and which fits this weapon as it's the heaviest rifle cartridge in the game. Another argument for doing it would be keeping the Big Gun cathegory specialised in close to mid range combat and not a sort of jack-of-all-trades.
The argument against that would be that Bozar as a BG would require a specialised, different build than a Minigun or LSW (which require fast shot and therefore eliminate any attempts at proficiency with sniping) - but if you follow these lines please do keep in mind that a BG sniper build would also be immensely effective with a Rocket Launcher due to high chance of a devastating critical hit (and you don't really need that additional AP that much anyway, because Bazooka is a scoot and shoot weapon), so a Bozar/Bazooka combo would outclass SG snipers in most situations in terms of versatility. Another argument against would be that SG would become a better version of EW, eliminating the latter from the battlefields - but I think that if Bozar had a smaller range than a Laser Rifle (so let's make it 40) and was less damaging than Plasma Rifle it'd be all good.
All in all, if Bozar was ever to enter the game I believe this would be the way to go.
