Craig,
You first sized the cases, then neck turned them... they seated fine, and with seemingly consistant tension. You then fired these and sized them again, only this time they had uneven tension.
If this is how it happened, the only way you'd end up with this is... uneven neck thickness.
Even if you used an expander ball, the necks would not have neen sized down the same if they were varying in thickness. Spring back qualities of the brass is the reason for this. The same thing can happen if using brass that's been fired a different number of times.
If you have even neck thickness, what you'll find is, that when you fire the cases they all measure the same diameter at the neck. When you size them, same thing... all the same. When you draw them over an expander, same thing (I.D. is different in this case). Now, introduce one that varies slightly, .0005" or so and you'll be able to measure a difference in diameter. This is because the spring back is not the same between them.
Bearing surface = actual length of the bullet that measures .308" in this case, and which fully contacts the bottom of the grooves in the rifling, and also the comes in contact with the neck on the case.
Is the bullet seated so deeply the bearing surface reaches the neck/shoulder juncture? I'm not sure what the middle was that you refered to? I'm assuming a 165 SST would not reach the juncture at that length, although the 178 A-Max is about .080" into the juncture at that lenght so...
The important thing is, the bullet will get tighter at that point because it doesn't sping back as much as the neck does, the shoulder is reinforcing it so it don't. It's best not to seat that deep if you can keep from it.
If a doughnut forms on the inside there, it just gets worse. I'd recomend a neck turner from K&M with the fluted reamer mandrel, this would cure all you're problems in one swipe.
The Forster will not get you the accuracy the K&M will, I've got both and that's why I ended up getting the K&M.
If you can't control the cut to the .0001" (ten thou) you're gonna have problems. The problem with the Forester is that the case head is held in the collet and will not float on the neck mandrel, and if it's not tight on the mandrel, almost to the point it won't turn on it, it will cut one side thinner than the other... the side the neck is torqued over to when you tighten the collet on the case head. It'll do it every time, really bad if the mandrel has anything but a super tight fit to the neck.
The K&M unit will be forced away from the cutter as it rotated about the mandrel, it doesn't have this problem, as it floats on it. The back cut on the cutter forces the case tightly against the mandrel and thickness doesn't vary no matter what you spin the case with. Let the tool float in your hand tho, as most case holders won't center the case perfectly.
Ken sells a great modified ball mic, one is really necessary if you want to see the actual deviation it's producing.
I must admit tho, with the Forester, I could easily see the deviation with a .001" capable dial caliper slipped over the case neck.
If you use a K&M, you won't need the mic, trust me, it'll be within a ten thou every time, so save your money. If you're worried about clearance issues with a fitted neck, measure the loaded diameter with the caliper and that'll work perfect.
The factory neck thickness is probably beter than you can do with the Forester, and I'd never use one to turn a neck again FWIW. I messed up practically every case I ever turned with mine.
My new 338 Lapua brass was never getting touched with it for that reason!
Hope that helps some, sorry for the long bla, bla, bla...
