My 30-06 with 165 gr and H4350 at 58 gr shows what appears to be flattened primers, just noticable. This is also the case with every factory load tried in this rifle. The factory loaded primers appear identical with those shot with my hand loads. So, I don't think it is necessarily a pressure sign. The expansion of the brass with the friction against the chamber is what actually holds the case from excessive thrust on the bolt face. However, just before the brass can expand to seal against the chamber walls, a loose chamber permits the case to edge back against the bolt face and this may be causing the flattened primers slightly. Severly flattened primers are obvious signs of pressure, but do not make the mistake of thinking one is not over acceptable pressure limits, when not. Another possibility is having the chamber contaminated with too much lube, like gun oil. The chamber should be dry and totally clean, when a tight swab is twisted inside it. Cases may not have all the lube removed from sizing. This allows the case to slip or not grab the chamber walls like designed. Hope this helps. I've done all the above and haven't had any decrease in the slightly flattened primers, either with factory or hand loads. Another way to check for high pressure in the case is to take a paper clip and bend on end at 90* just enough to fit down the neck. Insert it into the case all the way to the bottom and slowly drag the bent end along the case wall. This will indicate if any excessive case stretching occurs, as a hollow will form beyond the base about a 1/16" from the extractor groove. Any differences in case wall thickness at this point are signs of excessive pressure.
