I believe the " open" end and the lack of a boat tail benefits the partition to " slug" the barrel and keep the partition accurate where there maybe some crown damage or erosion in older rifles/ carbines.
The accubond having a solid boat tail base may let gasses escape as it leaves the barrel if the crown is not uniform.
Anecdotal evidence, I have two rifles that were recrowned that shot accubonds better after the work. ( but one also got a new trigger) so my observation may be biased.
