I've never built a kit, but gifted two to my father who did. Basically, unless you are looking to learn and enjoy the building process, there is little benefit cost-wise to doing so. You aren't going to save much money building a kit.
But, once you build it, they shoot as well as anything, assuming you built it well.
Twist rate is the rate of twist of the rifling. A 1:1" twist would mean that you made one complete twist in 1 inch. Obviously that is a very tight (fast) twist. The longer you have to go to complete the twist, the looser (slower) the twist is. For example, let's say it took one mile to complete one twist.
There is an equation, called the Greenhill Equation, that attempts to explain the relationship between projectile parameters and twist rate:
https://en.wikipedia.org/wiki/Alfred_George_Greenhill
This was developed in the late 1800s. There have been more modern adaptations.
But the long and short of it is that for any given bore diameter (say, .577 caliber), and all else being equal (hollow cavity, conical nose), the faster the twist, the longer (heavier) the bullet will need to be in order to stabilize properly.
I disagree with Hawg's assessment of conical bullets and their twist needs.
The quintessential Pattern 1853 Enfield musket had a 1:78 twist and fired a conical "expanding ball" bullet of about 530 grains. Likewise, the Springfield 1861 musket had a 1:78 twist and also used a conical expanding ball.
Musketoons like the Pattern 1858 Enfield had a 1:48 twist and tend to do well with heavier bullets to stabilize well but also historically shot conical expanding balls.
Of course for rifles like the "Kentucky" rifle you linked to was not a military rifle and was probably usually shot with patched round ball.
Steve
