Don't worry about it I like when I am questioned about my loads and fps numbers, I like answering them because I have nothing to hide and don't fudge the numbers since there is no need to. And to add to that these numbers can be repeated any time, any time, any place, and in any conditions. Not some nuclear lab under Ideal conditions, I have got even higher numbers than that I have posted but do not feel comfortable reproducing the load repeating them or posting the numbers.
As far as the brass RUM brass does not last no matter how you load it, so I say screw it and take no prisoners. And as far as pressures go I am sure I am above the 65000 mark but that does not mean that at 66000 evrything goes awry, that is not how it works there is some saftey built in. I could be at 70000psi or even 75000 for all I know, flat primers are a given so I don't go by that heavy bolt lift however is where I draw the line and back off, there are other signs but that is my main one and has never let me down. You can get away with higher pressures with light bullets since by the time the pressure Peaks the light bullet has already started to move forward and is dissapating the pressure, so the peak in pressure is there far less longer than it's heavier counter part IE:300gr And as far as the numbers there is no one thing it is a combination of Those TTSXs with there short bearing surface, the RL17, the long barrel, it's slow twist rate, NON MAG Primers also help in keeping the pressure under control, I also jump the lands 100 to 125 thou I suspect that chamber has a lot of free bore to which all helps with dissapating the pressure. all these things together make up this ungodly round. I have a shooting buddy who has a 700P in 338 Lapua that I load 100gr of RL17 and he gets 4000fps with those 160s He cracks me up he has those 50 round ammo boxes and when he goes to the range he has 40 rounds loaded with 300s and 10 with the 160s in the same box.LOL
Dean