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A couple possiblities not mentioned.....
the tracer bullet is much much longer than the standard ball bullet of the same weight. That creates much more drag and would indeed raise the pressure. If you had a little extra powder it probably wouldn't create much trouble with a normal bullet but a little extra and the long tracer might just do the trick. Another possibility is that H110 is too fast for that bullet and the combo of fast and hot could be just enough to create the blowout. I agree with some of the others that the chamfer/radius is more than generous and is in fact excessive. There is a lot of unsupported case that could contribute to a blowout. I do agree with your position that this is not the problem in the current case in question. There is a lot of excess with the primer and case head in that condition. The ejector formed a nice dimple as well with the case head flowing into the bolt face. I've seen some of this when using powders that are too fast even though the charge weight should be ok. 2400 seems to go that way with just a .1gr increase past what was working ok. I haven't blown any out to the extent you've shown but I have had some definite pressure signs with flowed case heads and primers. Another thing I've noted is that what works good in the bolt gun may blow the semi. I keep brass fired in the SIG separate from anything fired in a bolt gun due to differences in the case support which change how much stretching there is. Probably no simple answer to your case so use caution when using tracers or other large light bullets.
Frank
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