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Questions for Oom Driepoot and others that spend a lot of time in internal ballistic simulation programs
Simulations .. because there is no ACCURATE easy way to measure pressure - although it is possible to accurately measure velocity
Velocity and pressure are however not parametrically one to one linked !
My particular application is a bit different as my rifle has a very long throat - more than the total length of the [ internal] magazine so I have to load long ie. you can get more powder in the case
Seeing as the easiest powders to get are the VV ( not Vryheids Vront ) I have been running simulations in the N555 / 560 / 160 burn rate - 5 powders are double base 1 powders are single base
They are all quite close differing on load ratio - how much you can stuff into a case
Seeing as powder is so hellishly expensive one tries to find a powder that works needing less
I have found that QL and GRT differ quite a bit in their simulation of these VV powders
( It is possible that my powder files are not 100% up to date ? )
However what have the maestros discovered - from real World experience - with the above powders
What is more accurate in load simulation .. QL or GRT ?
Posted : 26/03/2026 12:41 am
My experience :-
1. QL - the propellant data and bullet selection is in most cases very old data. I started with QL in 2012. Speeds calculated are normally somewhat lower (even up to 200fps) - this can also be due to long COL and closeness to the lands.
2. GRT is sometimes surprisingly close with speeds, but can also differ substantially. N550 always gives higher speed than predicted. This might be true for most VV propellants.
In general I use data from the manufacturer's website and compare that with calculated predictions. Once I have charge, speed, COL (at least 1mm jump) and water volume of fired cases, I can calculate node charges and speed. If the first speeds are low, then normally extrapolating you can expect more speed as pressure passes 50K psi. A very good pressure range is 5K psi below max when looking for a node. Many top nodes do fall into the 50-55K psi range for a 60K psi max.
Posted : 26/03/2026 12:10 pm
Topic starter
My experience :-
1. QL - the propellant data and bullet selection is in most cases very old data.
Many top nodes do fall into the 50-55K psi range for a 60K psi max.
Thanks very helpful
Is QL data still very old - even with the recent update CD's ?
With a psi max on the larger calibres eg. 300PRC at 65,000 I am still wary at 60,000 as one is not sure of all the possible variables and pressure can spike quite quickly
Reloading manuals are also really only guides
I have found the best fill ratio / burn ratio / velocity comes in at the higher pressures
I hope someone develops a means of testing pressure that is available and affordable for private reloaders ...
Posted : 29/03/2026 9:25 am