Here is the fired brass from the 39.5gn loads. Let me know if this is signs of pressure. Thanks.
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Reading the primers is a sort of subjective and you won't get the same answer from any two people in most cases. There are signs that everyone knows are bad like ejector marks pressed in to the brass or a hole in a primer or signs of gas having escaped around the primer on new brass but the signs of excessive pressure is usually not that easy to define.
It looks to me like there are signs of pressure increasing with each of your loads and I would say that the 39.5gr load seems to be getting pretty close to the top end but the one thing I use to determine when the pressure is at the absolute top end is the flatness of the primer.
Some people will look for an indication that the primer material is beginning to flow around the firing pin (your 39.5 gr load seems to show signs of that, thats the little curl of primer material that is raised around the firing pin indentation) but I have found that some rifles and some primers can cause this to happen even when the pressures are OK. My favorite sign to look for is when the primer has been flattened to the point where there is no real gap between the outside edge of the primer cup and the wall of the primer pocket in the brass. Your pictures don't seem to show that happening yet. Oh, and don't misunderstand, that gap will start to get smaller in increments so what I'm saying is watch the gap for signs of it getting smaller and when you see that it is getting smaller than you are just under the max pressure that I would be willing to work with. Eventually the gap disappears and when that happens your brass is really taking a pounding. In fact I throw my brass away if I see that happen because chances are the case will split within another reload or two.
The one thing that will affect the pressure very quickly is the volume in the case. Anything that creates less volume will raise the pressure. Seating the bullet deeper or using a bullet that is longer than another will lessen the usable volume of the case and that will cause higher pressures. So while I say that your 39.5gr charge weight should be OK it might be getting hotter than it would for me because I might assemble the cartridge a little different than you.
And most of us seem to find the best charge weight for the 168gr bullets is somewhere around 40 - 41.5 gr of IMR 4895. But every rifle is unique and you need to take all the appropriate safety precautions while you work up to the load you're happy with.
