A swamped barrel is one that tapers from breach towards the muzzle, but then flairs again for the last 8-10 inches.

And yes, a 62 is for bigger game, but of course can be used on smaller game too. A 12 gage slug is not thought of as big in many places, but they are about 70 cal.

A 62 flintlock such as this one will throw a 320 grain ball at about 1800 FPS. It kills VERY well, and when cast from a hard lead alloy, it will exit American Bison and Moose in nearly every case on quartering and broadside shots.

Accuracy in not dependant on caliber at all. It’s just a function of quality of the barrel, and how well the barrel is inlet. All Round Balls have the same Sectional Density. The B.C. goes up some as they get bigger.
So range is a function of velocity.
It’s easy to get about 1850 FPS out of round balls from 22 cal up to about 66 cal. So the 66 will shoot flatter then the smaller calibers because it’s BC is higher.

Like with shot, a 12 gage has better range with #2 lead shot then it does with #8 lead shot, even when both exit the muzzle at the same speed. Big balls retain velocity better then little ones.

Now when we get to about 66 cal, the issue get more complex. Recoil becomes a factor.

So some “big rifles” are sot at slower speeds then smaller ones, but that because of comfort, not because the big ones could not fire such a load. The shooters can't handle such loads.

But lets’ look at physics;
A 600 Nitro will fire a 900 grain bullet at about 1900 FPS. From a 16 pound double rifle the recoil is noteworthy.

An 8 bore muzzleloader can be loaded to fire a 875 grain ball at 1850. Only 50 FPS less, and only 25 grains less bullet.
But an average 8 bore rifle will only weigh 11 pounds!
So we load them so as to be useful, not to gain velocity

If we look at a 4 bore, we now have 1750 grains of lead. At 1000 FPS the recoil looks like this;

This man is 5 foot 9 inches tall, and weighs 170 pounds The rifle weight 17 pounds 4 ounces and was loaded with 375 grains of powder that’s only 900 FPS It still kicks.

With 475 grains of powder it will achieve about 1350 fps Recoil is more then what you see here with a 475 grain charge.
At 1850 FPS it would be very close to a 600 double, if you pulled BOTH triggers at one time.
I think I make the point………….

I have made a lot of 62 cal rifles. Recoil is not bad at all with 150 grain charges.
A 66 cal will use about 165 grains to 175 grains
A 72 cal will use 180 to 200

An 8 bore uses charges of about 325 grains.

4 bores use what ever the shooter can handle starting with about 300 and going up to the human limit of the shooter.
A 2 bore is a REAL mans gun.. Here’s the ‘skinny end’ of one.

That's my hand. I have average size hands.
Here's the rifle. I made it for "big Dog" on this site.

I have only made this one 2 bore. My old apprentice Colin Srolzer has made more true 2 bores than any one I know of, in the last 200 years, and that’s still only 3 rifles. He posts on this site from time to time.

But, to answer the questions,
#1 yes, I will make about anything you can ask for if it loads from the muzzle,
and #2 the range is limited by how much recoil you can take on the big guns, and how tall you want to make the rear sight. Keep in mind that muzzleloading cannon have range measured in thousands of yard, and they are all effectively the same kind of gun as a sporting rifle, but made a lot bigger.