Had an extra short barrel for the Zius BK2S and used the Thread16mm model from the Rev 2 EX BCAR. by Epicxxxx to merge both barrels. Makes it about a few inches longer than the BK1S barrel. I can't say much for a performance improvement but I like the way it looks. I left the collet blank in case you want to customize it. As mention on Rev 2 EX BCAR. model page - tolerances call for .12 layer height print settings.
The author remixed this model.
Remixed threaded barrel mount model to allow for the extension of the barrel and removed smaller smaller end used for bcar attachment.