What are the benefits, besides cost, of a smooth rifle?
Do they load easier than a rifled gun?
I guess you can use shot in them? Would a .45 smoothy be too small to get a useful load of shot in?
Well first, if you have one built, you're probably not going to see a cost advantage by much if at all. You get that advantage these days when you find a rifle (usually a factory job) that the previous owner
roached the barrel due to improper cleaning, and the cost is barely for the remaining parts. THEN you send it out and have it bored smooth.
Since they do not require a tight fitting patch to engage the rifling, they do load round-ball easier. You can't use conicals, which I'm sure you know, but I just mentioned it here for anybody new to the hobby who isn't quite up to "full speed" on smooth rifles.
Of course as mentioned above you can use shot in them. Their thicker barrel walls in many cases allows the shooter a bit more powder and shot. As Britsmoothy mentioned, he's shooting a 3/4 ounce of shot...that's a light 20 gauge load, or a heavy 28 gauge load and is well above the .410 shotshell here in The States.
As for buckshot..., I don't think you get an advantage here, especially if you're in a smoothie below .50. Might as well just use a patched ball, or if it's legal (as many states require during ML deer season a single projectile) loading a double-ball load. The double-ball might be problematic, there are additional concerns..., both being seated and remaining seated against each other...., the loss of velocity vs. the advantage of the extra ball (or adding more powder)...etc.
You're talking in most cases a 50-60 yard gun with a single projectile. For me in the terrain where I hunt that's not a problem at all. And you do get small game capability.
LD