Personal experience with CBs and shorts vs longs:
My 14" match chambered Contender loves them. I always assumed better accuracy from longs due to less bullet jump, until I bench tested.
The shorts consistently grouped better, and in a hunting senario, i.e. Shooting overhead on steeply downwards, had fewer fliers. I attributed this (perhaps wrongfully) to the same charge in the two different cases. The longer case allowed more air space for perhaps inconsistent ignition before the bullet released from the case mouth. Could all be bunk, but I couldn't argue with the grouping.
Remington 550-1 and Gevearm are the only autoloaders I've owned that cycle CBs, the shorts, and it's real fun to go pop, pop, pop, with zero recoil!
Take care,
warren