The latest responce from Remington :
When our engineering department designs any particular model, all variables or enhancements are taken into consideration.
In our Model 870, the initial design of a barrel is tapered as in a forcing cone design. We found that a "lengthened forcing cone" such as is featured on sporting clay models did not improve accuracy or performance. As there was not a significant factor with this feature, we did not include the feature.
Have a good day!