GRT Users - Question on Burn Out

[Martin52]

Generally, I understood 1) slower powders achieve full burn closer to the muzzle, faster powders closer to the chamber and 2) an early burn (closer to the chamber) is preferred for improved consistency of muzzle velocity.

My results in GRT seem to show the opposite. Using the Sierra 2156 155 grain projectile and comparing Varget, H4895 and IMR 8208, it is Varget that achieves the fastest burn. This is in a 31.88 inch barrel, COAL 2.824 inches, Lapua case capacity 55.9 gr H2O

According to GRT, Varget achieves burn out at 16.5 inches, 8208 at 23.1 inches and H4895 at 28.7 inches. These are at the predicted OBT nodes.

This question is am I correctly interpreting what GRT Burn Out means, or is it something else ?

TIA

Martin

 

[jelenko]

What volumes of powder are you using for Varget, 8202 and H4895?

 

[Martin52]

Thanks,

45.06 gr Varget
44.6 gr H4895
43.6 gr 8208

 

[jelenko]

Here's what I get with a Win 308 chamber, 32 inch barrel:

45.06 gr Varget Burn out at 30.13
44.6 gr H4895 Burn out at 16.6
43.6 gr 8208 Burn out at 23.8

 

[Martin52]

Your numbers are closer to what I originally expected, at least for Varget at 30.13 inch burn - although I would have thought 8208 (23.8) would burn closer than H4895 (16.6).

In my calcs the problem appears to arise because I have been modelling powder changes in the same file, each subsequent iteration may still contain links to previous data. I am going to start fresh with a new file for each powder and see how that goes.