Not really sure if I can answer all of your questions, but will try.
Yes T/C has indeed made their .30 Caliber Contender Barrels with two different twist rates. In addition to this the two different twist rates also have different Rifling Configurations.
The OLDER .30 Caliber Barrels featured a conventional 6 Land & Groove Rifling Configuration and had a Twist Rate of 1 in 14".
The NEWER .30 Caliber Barrels featured an Equal Land & Groove Rifling Configuration with 8 Lands & Grooves, and had a Twist Rate of 1 in 10".
I do not have any idea as to the year of manufacture that the change was made. To find out what you are looking at, simply count the number of lands and grooves in the barrel, and that SHOULD give you an idea as to whether it is a 1 in 10" Twist Barrel or a 1 in 14" Twist Barrel.
There has been a lot printed about which is better or more desirable. Spectulation has it that the older 6 Land & Groove 1 in 14" Twist Rifling is more accurate, buuilds pressure slower and more gradually, and yet produces higher velocities.
Case in point myself and 3 of my friends are all shooting the .30-30 Ackley Improved. Two of these barrels have the older 6 Land & Groove 1 in 14" Twist Rifling, and the other two have the newer 8 Land & Groove (Equal Land and Groove) 1 in 10" Twist Rifling. At one point in our load developement all of use have shot the same exact load. Granted there may be minute differences between any of our powder scales, but for the sake of arguement, the load was the same amount of grains on each of our respective scales. The accuracy level has been very similar, and in fact the one person is wringing out a little better accuracy out of his 8 Land & Groove (Equal Land and Groove) 1 in 10" Twist Barrel. The other interesting point is the velocities we are all obtaining with this identical load are all but identical. Without going back to my notes to look I believe that all of the average velocities from each barrel are within 50 FPS of each other.
Hope I answered some of your questions.
SD Handgunner
