Full length sizing done the right way has always produced ammo that shoots bullets most accurate. Sierra Bullets proved that back in the 1950's. Competitors shooting matches hand holding their centerfire rifles in 3 positions learned that long before then. It's my opinion the benchrest folks didn't believe it until several years ago when they finally learned it made their largest groups not quite as big. Their smallest groups stayed the same size. The key part of it is setting fired bottleneck case shoulders back no more than .002" for bolt action rifles so the case headspaces on its shoulder; not the belt on such cases. Sometimes a custom full length sizing die will be made that sizes case bodies down only .001" and their neck diameter is .002" smaller than a loaded round's neck diameter. Forster hones out their full length sizing die neck for $12 to what the customer specs. Redding or RCBS full length sizing dies with bushings sized the same are probably the best commercial dies made. They all end up making case necks better centered on case shoulders as well as the straightest. Neck only sizing dies don't keep the case body aligned with the case neck when the neck's sized down. Expander balls bend case necks a bit on their way up and out of the case neck.
Belted cases usually need their body diameters sized back down all the way to the belt. Standard dies stop short several thousandths and the tiny ridge in front of the belt on fired cases interferes with the chamber belt stop a little bit. A collet die from Innovative Technologies - Reloading Equipment solves that problem. Years ago, people cut the top and bottom off a standard full length sizing die then used it after normal full length sizing to size the case body back to virtual new case dimension right in front of the belt to get rid of that ridge. Otherwise, they used new cases. I've not seen any difference in accuracy with my 30 caliber belted magnum match rifles with new or properly sized fired cases; both have shot 20 to 30 shot test groups at 1000 yards in the 1/2 to 2/3 MOA range. I don't prep cases in any way other than sort them by weight to a 1% spread.
Bullets are centered in chambers best by having the case shoulder center in the chamber shoulder when fired; they all are from firing pin impact. Doesn't matter how much clearance there is around the case body. The case body at its pressure ring is always pushed against the chamber wall by the extractor pushing it there; no other part of the case touches the chamber wall so it doesn't matter how much clearance their is around the rest of the case body to the chamber.
New cases almost always shoot most accurate in rifles whose bolt face isn't square with the chamber axis. Their case head impacts the same place around the bolt face at its edge when fired so the barrel vibrates/whips in the same axis for every shot. That whip axis is typically right angles to the lug axis on a 2-lug bolt. That case head is now flattened against the bolt face at peak pressure and it stays that way. Resizing that case doesn't square it back up again. When its fired again, odds are it's not indexed the same way in the chamber so its high point will now impact the bolt face some other place around its perimeter when fired. That makes the barrel whip in a different axis before the bullet's gone; the bullet takes off in a different direction that desired.
I also suggest you judge a load's accuracy by the biggest groups they shoot. Smallest groups happen when all the variables cancel each other out; or when they're all at zero. Odds are in heavily in favor of them cancelling each other out. Biggest groups happen when all those variables add up in different directions.
Belted cases usually need their body diameters sized back down all the way to the belt. Standard dies stop short several thousandths and the tiny ridge in front of the belt on fired cases interferes with the chamber belt stop a little bit. A collet die from Innovative Technologies - Reloading Equipment solves that problem. Years ago, people cut the top and bottom off a standard full length sizing die then used it after normal full length sizing to size the case body back to virtual new case dimension right in front of the belt to get rid of that ridge. Otherwise, they used new cases. I've not seen any difference in accuracy with my 30 caliber belted magnum match rifles with new or properly sized fired cases; both have shot 20 to 30 shot test groups at 1000 yards in the 1/2 to 2/3 MOA range. I don't prep cases in any way other than sort them by weight to a 1% spread.
Bullets are centered in chambers best by having the case shoulder center in the chamber shoulder when fired; they all are from firing pin impact. Doesn't matter how much clearance there is around the case body. The case body at its pressure ring is always pushed against the chamber wall by the extractor pushing it there; no other part of the case touches the chamber wall so it doesn't matter how much clearance their is around the rest of the case body to the chamber.
New cases almost always shoot most accurate in rifles whose bolt face isn't square with the chamber axis. Their case head impacts the same place around the bolt face at its edge when fired so the barrel vibrates/whips in the same axis for every shot. That whip axis is typically right angles to the lug axis on a 2-lug bolt. That case head is now flattened against the bolt face at peak pressure and it stays that way. Resizing that case doesn't square it back up again. When its fired again, odds are it's not indexed the same way in the chamber so its high point will now impact the bolt face some other place around its perimeter when fired. That makes the barrel whip in a different axis before the bullet's gone; the bullet takes off in a different direction that desired.
I also suggest you judge a load's accuracy by the biggest groups they shoot. Smallest groups happen when all the variables cancel each other out; or when they're all at zero. Odds are in heavily in favor of them cancelling each other out. Biggest groups happen when all those variables add up in different directions.
Last edited:
