hi guys i'm having my very first rifle built. its on a high wall i've had for 35 yrs. we're using a mark chenyln barrel 6 mm 8 in twist. i needed a rimmed case so after much research i decided on the 240 cobra, 220 swift necked to 6mm). the only data i've found is in ackleys vol #1. maybe some of you oldtimers might have some info you could pass along, also maybe some do's and don'ts. any info will be greatly appreciated thanks md