I was somewhat uncertain if their explanation for how they got 3100 fps (in the comments section of the link, above) was compelling.

First, they used a 24 inch barrel, which ostensibly gives the slow-burning powder more time to propel the bullet (though he said they had to use less powder in the longer barrel. Question: is that because the pressured gas stays in the barrel longer, making a load safe for a shorter barrel unsafe for a longer one?). Okay, it makes sense that a longer barrel contributes to a higher fps.

But I then got lost when he said something in a response about how their bullet "has lower friction because of a small bearing surface...and out of a high quality custom barrel." Not sure what "small bearing surface" means, and why a custom barrel is likely to shoot quicker than a factory one.

As for measuring pressure, I find no evidence they did anything other than check for "signs of pressure" like REM7600 says we hoi poloi must.

One curious thing was that he claims using CCI 400 small rifle primers creates "extraordinarily consistent MV of 3040 fps." Based on what people said on other threads about getting (what they perceive to be) a temperature-sensitive powder to burn in the first place, I would have thought people would suggest a hotter primer to get a slower-burning powder going---but again, I have no experience in such things. I'm merely highlighting where I cannot follow the logic in what these guys have done at their outfit when choosing a primer, if there is a logic to it other than just seeing what works.

REM7600, could you shed some light on what you mean by emphasizing that you were shooting a semi-auto when checking for warning signs, or point to a resource that might explain it in such a way that I could appreciate it, better? Perhaps I'm seeing an emphasis or connection that isn't there, in which case I beg your pardon.