For my two cents worth: don't be concerned about the rim. Have you heard of the 220 swift arrow?same capacity as a Swift, but Sam Wilson of Wilson reloading dies fame straightened the case, necks it down with a 30 degree shoulder, thus an even longer neck. You fire th standard Swift case in the new chamber to form the much improved case-no more case stretching! I used this ina Savage single shot and their 1-12 twist barrel allowed a 70 grain bullet and incredible accuracy with the stiff, single shot action. This refined and sophisticated varmint cartridge needs a 26 inch barrel and the right powders to really glean that finite, flat accuracy it is capable of. 220 Arrow reamers can be borrowed from Wilson, who also has the dies, of course.