So I was necking down virgin 6br brass in my Redding type S FL bushing sizer and ran into some problems, hoping someone here might have an answer. My first pass was with a .260 intermediate bushing, neck was sized all the way down to the shoulder, Bo problems. Next pass was with the final .249 bushing. This one left about an 1/8” unsized. Die won’t go in any farther and is bottomed out on the shell holder, it it shouldn’t need to since the previous bushing sizer the whole neck!
With the die bottomed out, hopefully you're not bumping shoulders back. Does the sized down brass chamber fine in your rifle? If so, load em and send it. This brass will for to your chamber and all will be well. All bushing dies will leave a small portion of the neck unsized.
Chances are, the intermediate bushing was leaving a small portion as well, but it's much less detectable when it's only 005 per side, now it's 010 per side. The only way to eliminate this, is to use a Hornady or equivalent 22cal neck sizing die. They're designed to size the neck only, but completely.
The problem is, going from 268 to 244 the the expander ball to 248, it's a lot of working the brass, and runout occurs. Using an intermediate bushing prior to the neck die helps a lot. But that's a lot of damn work to do when the stuff needs formed anyway. My heavily runout brass shot half moa breaking in the barrel, its a BR variant, it'll shoot.
Neck down with the bushing die as far as you can, but do not shoulder bump, as long it'll chamber(a small amount of resistance on bolt close is okay) load and shoot! Second firing that bulge at the base will be gone. Another tip, make sure you're bushing retention stem is screwed down to where it's tight against the bushing, and back out 1/8th a turn, just enough for the bushing to float, then lock the retention stem into place. This will ensure you're sizing as much neck as possible without bumping the shoulders.