The main problem with the doughnuts is that the SD is not consistent, most of my other "good" rifles
will hold SD numbers below 10 easy where this rifle while very accurate the SD will be much higher and all over the place due to the neck tension variance.
At 100-200 yards it does not account for much but at 500-700 yards I get noticeable vertical dispersion.
Now I know from the comments that what I am seeing with the necks is not so uncommon.
I have not noticed any issue with excessive ES/SD where I am seating bullets with the bottom of the bearing surface well below the donut, which I found surprising, because I had really thought that's exactly what I would observe. In your situation, it may be that extending the freebore of the rifle so you can seat bullets further out in the neck (above the donut), or reaming out the donuts, may be the only approaches that really solve the problem. Before I went to either of those extremes, I'd want to be very sure the vertical dispersion at longer distance was do to excessive ES/SD, rather than an easily correctable issue with the load itself. You can certainly run the numbers in a ballistic calculator yourself, but it takes what I personally perceive as a LOT of velocity variance to make a significant impact on vertical, even at 1000 yd.
As an example, a common F-TR .308 Win load is running the Berger 200.20X bullet over Varget or N150 at ~2650 fps from a 30" barrel. An ES of 20 fps should theoretically still give [barely] X-ring vertical at 1000 yd (0.5 MOA). The same holds true for .223 Rem load I have used many times at 1000 yd, with 90 VLFDs over H4895. Now, I'm not saying that such loads are ideal, and you'd certainly run the risk of dropping points "out the corners" with loads like that, but they wouldn't necessarily kill you in terms of vertical at local matches. Another important point is that I used "ES" values rather than "SD", which in theory will better define the extreme vertical dispersion on the target than SD. The key point is that by definition, the ES is defined by the highest and lowest velocity shots; i.e. only two shots out of the total number fired. In general, SD values typically run less than half the value of ES for the same number of shots (where N>/= 5 to 10 shots, or more). It's a little more complicated than that, but I think you get the point I'm trying to make about assessing the effect of velocity variance on vertical. In any event, it may be that a simple adjustment of charge weight and/or seating depth might largely solve your problem. Obviously, there are no guarantees of that, but it's fairly simple and of minimal effort to test that before undertaking something like reaming out donuts on many pieces of brass, or throating out the rifle and then re-working a load from scratch.
In any event, best of luck with it, and let us know of you are able to solve the issue.
