Allen, Yes, you should be roughly 28.7 when you hit recommended max pressure, plus or minus a little for your specific gun.
I don't think Vihtavouori publishes data for a 115 grain bullet with N-140.
However they do show data on the web for a 105 grain bullet and also N-140.
Along with the 105 grain, you can get a feel for the difference to your bullet by a look at the trend between the 105 and the next lighter one. Here is what that looks like.
When they don't specifically show you the pressure, you can assume that they will not go over the CIP specs for a given cartridge, so assume this is at or below the cartridge max of roughly 58.7 KSI.
So for the above example, let us assume a 6 BR with 28.9 grains of N140 and a 105 will be roughly 58.7 KSI for talking purposes.
Next step is to look at the lighter bullet and see that we are lucky they show N-140 again. Here we see 29.0 grains. So for an increase of 5 grains in bullet weight, we got to pressure with a decrease of 0.1 grains and had roughly the same speed for that 100 grain bullet.
Next, if we have nothing else to go on, we would assume another 10 grains of bullet weight would put us at pressure A) with more powder than the loads shown, or B) with less powder then the loads shown?
To play things safe, the answer would be B, it will take less powder to hit pressure with an increase in bullet weight for a small perturbation around known data. This is a general rule when experimenting with no load map and without the use of a tool like Quick Load or Gordon's Reloading Tool.
Now if we look at the Sierra data listed on this web site, we will find the following:
So, let us assume a 107 grain bullet with 27.5 grains of N-140 was near 58.7 KSI. We now have yet another sample of published data for a different bullet, but close to the one we want to try. We combine it with what we found above, where a 105 grain bullet used 28.9 grains to hit assumed pressure.
Now using the published data for a 105 grain, and a 107 grain, when we extrapolate to a 115 grain and assume the trend would be less powder for heavier bullet, we would have to assume the top end should be less than 27.5 grains shown in the Sierra manual.
We see from the QL chart, that their estimate is climbing roughly 5 to 6 KSI per grain of powder near the top. That chart shows 27.5 - 28.5 as the last step before you get flags and are likely hitting their max recommended pressure.
So the rifle to rifle differences in better quality rigs is easily on the order of 5 to 6 KSI and that amounts to the possibility that you get roughly a grain of difference between folks when it comes to max. Keeping in mind QL also assumes somewhere between 2560 to 2650 fps at the point where you hit max recommended pressure. So, it is also good to chrono yourself to see how you sit with respect to known load maps.
Even doing load ladders and watching your brass, you should always do the above homework before you set out at the range to keep out of trouble. Play it safe. Good Luck.
