Pressure in measurements but not with traditional signs?

[SDHNTR]

So I’m getting significant growth in base diameter of Alpha brass in my 6 GT. No ejector mark, no flattened primers, zero stiff bolt lift, but the base (just above extractor groove) diameter is growing a lot. .0015 to .002”. That’s a lot more than I’m used to with other cartridges. I ran this same load up another 1.8 gr of powder before I saw even the faintest ejector mark. I’ve never seen this kind of brass growth without other pressure signs showing up before. Ideas?