Shot Start/Initialization Pressure Adjustments in QuickLOAD

[jepp2]

True, the powder is not always, most often not, consumed at peak pressure,

This statement kinda confuses me. Peak pressure tends to occur somewhere around just over 2 inches of bullet travel down the barrel. The powder is 95% consumed somewhere around 10 inches of bullet travel down the barrel, and completely burned at ~22 inches of bullet travel down the barrel in the graph I'll share. Different for different powders of course.

The only reason the bullet continues to accelerate during the path down the barrel is because powder is continuing to burn and generate gases to drive it. Otherwise it would start slowing down as the volume behind the bullet increased for the gases that aren't.


And regarding start pressure changes vs bullet seating depth. As seating depth increases (shorter OAL) case volume decreases which increases pressure. As seating depth decreases (longer OAL) case volume increases which decreases pressure. Add in bullet movement prior to encountering the lands and the effect this has on start pressure. These two factors cross at some point. Here is a graph showing the point where these cross based on a study that was done some year ago.

 

[BCBRAD]

I meant to say deterrent chemicals are consumed by peak pressure, the Z1 line been an indicator.

And, yes there are diminishing returns as you go deeper on bullet seating, which is ~1/4" as illustrated in the graph.

In your sample for the 25-06 , RL-19 is 'fast' for the combination of components as the Z1 line is to left of peak pressure indicating the powder burns uncontrolled , as it does not have the benefit of the deterrent chemicals after that point (z1).

 

[chop house]

exc discussion. thx all. tag

 

[davide]

Interesting topic, where the value 290 is coming from ? It’s a valid value for every bullet and caliber ?
thanks for replay

 

[BCBRAD]

Interesting topic, where the value 290 is coming from ? It’s a valid value for every bullet and caliber ?
thanks for replay

In the shot start pressure drop down there are notes on differently constructed bullets.
Suggest you develop a model and insert 10 825 psi in the start pressure window, this indicates a 'touching' lands for the bullet, so add 7200 psi to the default of 3625 psi for 10 825 total psi.
Now, noting the overall pressure in the results window, reduce COL 0.010", the overall pressure in the start window will be ~290 psi less.
The drop down suggests 146 psi, I calculate this to a little less but use the 146 psi number for every 0.005" off the rifling. The default is 3625 psi and represents 0.247" off the rifling after which there is limited returns (see graph in post #21. Doing this will keep your Ba tweak (to align actual velocities to the model to less than 5%) 1-2% is typical if the program is run properly. The 5% represents up to normal powder lot to lot variances.
Some operators of QL do not agree with this approach, I have discovered they deal with 1/2 nodes, finding a node, and adjusting Ba up to 13% in one sample, and mix traditional methods to get a good shooting load.
Suggest you try it and report back.

 

[davide]

Thanks

 

[Murray Brook]

Very interesting stuff.