Re: New problem, need expertise!
If an ackley chamber is headspaced properly seating bullets into the lands is completly unneccesary when fireforming.
Heres why, a standard 25-06 chamber is cut to the go gauge, or with-in a thou or two. This allows the bolt to close on new brass with no resistance.
An ackley chamber should be headspaced to about .004" bellow the standard 25-06 go gauge. This is so that when the bolt is closed on new brass, there IS RESISTANCE. That resistance is the leading edge of the case shoulder being crush fit into the chamber shoulder at the neck juncture.
When done this way the brass can not move forward from the plunger(although I like Chads Idea of removing it) or from the fireing pin strike. It is locked in place so only the shoulder and case walls are expanded, and the web does not stretch.
If at all possible when you have an akley built send the smith 20 pcs of brass from the same lot, that will feed the rifle for it's life. Then smith can modify the headspace to put a precise crush fit on the brass YOU will feed the gun. Now the whole web stretching issue is a nonissue.
This is also why a factory tube can not be acklied properly without setting the barrel back some to produce the crush fit.
Now the problem with your gun as I said earlier, UNDERSIZED brass at the web dia. (measure your webs and compare them to a saami spec for that chamber) did you try that yet? The other possibility is an oversized reamer created a chamber that is a touch too big. But my bet says it's a brass size issue, I seen it on a 280 ackley with rem brass that measured .464" at the web.