Here are two more SSK cartridges I have. 6.5 Mini-Dreadnaught JDJ based on the 220 Swift case and 35-06 JDJ both have 60 degree shoulder and short neck. Pretty sure all of the JDJ cartridges for the Encore have short necks. Never had any issues with them.
257JDJ Contender based on 225 Winchester has a short neck too.