Have you measured case head expansion? This is what I would be looking for.
I have actually, though this is my first time doing so, and I left that data out because my method is somewhat primitive. Also, it seems like a very controversial way to check for pressure, some people say it is very accurate, others say it is useless. I just went off of what Hodgdon reloading data said to do, this is how I measured. First issue, I don't have a blade mic, just a simple set of rcbs calipers, but I did find a way to measure the web just in front of the extractor groove that yielded consistent measurements. I have to roughly estimate where the needle falls in between the thousandths, but I do believe I'm able to get within .0001" of the actual measurement. I was not able to measure each load prior to fireing, then again after firing, but upon measuring the remaining 10 unfired cases (as Hodgdon stated you want to start with virgin cases as they work harden) they were consistent, only varying about .0002", with the largest of them at .5810", and the smallest .5808", though there was only 1 of the 10 at .5808", 2 at .5809", and the remaining 7 at .5801". When I was going through this I measured every case 3 times, and every time came up with the same number.
According to hodgdon, a .223 case will stretch .0004"-.0005" at max, cases like .270, .308, 30-06 and such will be at max around .0005"-.0006", cartridges like 300 wm and 7mm rm will be at max around .0006"-.0007" stretch. It did not state what cases like the Lapua and Norma should stretch, though I think it would be safe to say, they would likely tell you .0007"-.0008". It did not say a specific pressure this would be, and that makes sense, as different cases will stretch differently (a lapua case would likely stretch less than a soft hornady case under the same pressure) however it may show what the limit is for that specific brass, which is generally what we look at with other pressure signs, such as primer pocket expansion, ejector swipes, etc. Hodgdon also stated that you must watch for other signs of pressure as well, don't rely simply on this measurement.
Anyway, here is what I ended up with.
H1000 had all .5810" up until 88 grains which was .5811", 89 was .5813", and 90 also .5813". Throwing in my variables, max charge could have been as much as .0006" stretch or as little as .0002", likely .0003" stretch. According to this, I didn't reach max.
With Retumbo, 87 was .5810", 88 was .5813", 89 was .5816", 90 was .5815", 91 was .5815", 92 was .5818", and 93 was .5819". With variable at max charge, as much as .0012" stretch or as little as .0008" stretch, likely .0009" stretch, and max would be around 91, or my 2884 fps load.
For Reloder 26, all were .5810" until 84, which was .5812", then 85 was back down to .5810", and 86 was .5811". Up to .004" stretch, as little as .0001", though I feel I didn't reach a max here if going off of this info.
Finally is Ramshot, which I had 2 of every load on this one. 86 was .5809" and .5810, then all loads were .5810" up until 92, one was .5811", the other .5810", then at 93 we had .5810" and .5813", then 94 were both nack ad .5810". So again, somewhat inconclusive, or a consistent "max" was not attained.
Now, I take this data with a healthy dose of salt. I know my measuring methods, while they did show some consistent increase as velocity rose, are primitive, and open up a large door for inconsistency, and measuring case web is not the best way in many peoples opinion to get a good idea of pressure, and this is the first time I have done it. I only did it to attempt to get some more data on this. And I am not putting much weight in it, though I do think it shows a significant increase in pressure with the upper retumbo loads, obviously more than any of the other ones, which corresponds to the velocity I was seeing. Even still, I have no idea what that pressure is.
I'll leave a link to Hodgdon's information on measuring case web. I know many people that do this say there is better/different methods, I jist went with Hodgdon because, well, they are Hodgdon, not some guy on the internet I don't know.
https://www.hodgdonreloading.com/re...-trick-monitoring-pressure-your-rifle-reloads
One more thing, sorry for the novels. I like to add a lot of detail. Appologies.