Originally Posted by PhillipM
Why did full length sizing work better? RCBS does make a neck die but it's $60!!
There's not much details between a proper full length size belted case and neck only sized one except the body diameter's are a bit smaller. That ensures the normal out of round that both chambers and cases have won't cause interference between the case and chamber when the case has a tight fit. Plus, virtually all belted cases get a tiny ridge right in front of the belt when they're first fired. If that's not sized back down to the same diameter as the rest of the body at that point, it'll interfere with the headspace shoulder at the back of the chamber. Such interference doesn't let the back end of the case be at the same place across all rounds fired. Innovative Technologies - Reloading Equipment
now has a collet die to size that ridge back down and should be used after normall full length sizing die's have reduced body diameters back to about new case dimensions.
Sierra Bullets' has been full length sizing all their belted cases testing bullets for accuracy since the 1950's. Martin Hull, their first ballistic tech, tried every sizing method known to man testing their most accurate bullets to see what reloading process produced the best results. He was also one of the top long range competitors in his day. They still do that today with SAAMI spec (or virtual versions thereof) chambers using a .300 Win. Mag. test barrel checking 30 caliber bullets 190 grains and heavier for accuracy. They use Redding full bushing dies for cases those dies are made for, regular Redding full length sizing dies for all the rest. Their best heavy 30 caliber match bullets shoot under 3/8 MOA at 200 yards from fired cases so sized.
Martin Hull had a saying about how a bottleneck case should fit the chamber that's oft times been quoted by many top rifle competitors over the years. It goes something like: "The case should fit the chamber like a terd in a punch bowl.
" In other words, a lot of room around it. A tight or close fit of a bottleneck case to the chamber's not good for best accuracy. If one understands the details of how a bottleneck case centers in the front of the chamber when its fired, they'll probably understand why some clearance around the case body's better than only a tiny bit or none at all.