My action is a one-off BAT.
True single shot, controlled round push feed, standing blade ejection, larger/magnum tenon diameter, coned breech, extended port.
The loading tray was reamed correct diameter & centered height for WSSM.
Pretty sure feeding would not be an issue with this at any degree of shoulder, including negative (which has potential).
But I went 35deg shoulders and reduced body taper, which was easiest to exactly match 260AI capacity (perfect for 140gr bullets).
I could now move shoulders back a bit for a higher shoulder angle while keeping this capacity.
An actual Ackley improvement is a little more comprehensive in that it's designed for crush fit of new brass at neck-shoulder junction.
This negative headspacing is for fire forming, so I went with that plan.
With taking shoulder angles higher, the neck-shoulder junction (and neck) pulls back with forming. I accounted or this as well while choosing chamber end clearance/trim length.
I mentioned earlier that I went fitted chamber. This is 1thou over ENTIRE new brass dimensions. Necks turned to 13thou for .290 loaded.
At a 65Kpsi mid-node (for this cartridge) and 35deg shoulder, the ONLY sizing I do is 1thou shoulder bumping.
Perhaps going more extreme with shoulders will eliminate the eventual need for bumping as well. Probably the only change I'll make.
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