QuickLoad vs Chrono'd Velocities; Effect of Shot Start (Initialization) Pressure

[Straightshooter1]

I do, to me it is the most consistent way to adjust the powder lot you are using to the results you are seeing. I wasn't smart enough to discover this myself, but I can follow the lead of others. So here is the process I use:

http://www.the-long-family.com/Tuning QL to achieve best results.pdf

I also use the OBT barrel time QL provides to help me find nodes. I adjust the Ba value to make my velocities match so I get the ms of barrel time.

I do the same and find it works out quite well in saving time and components when making changes with the cartridge (like changing bullets or changing a long hand fed COAL to a much shorter one to fit into the mag, etc).

 

[RegionRat]

I'll add just a little food for thought.

In addition to the points already made about the initial pressure of OTL or ITL seating, as well as the use of the Ba and mass, there is a concept I will suggest that helps match up your data...

If you think of doing a charge ladder as having each step as an opportunity to tweak the GRT or QL model, then using the initial pressure for seating as an offset, and the Ba as a gain factor is a way of using many points to match the performance instead of just one.

Use the Ba to try and match the over all change in speed per charge, even if the points are a little lower or higher, then use the initial pressure to close that gap. In a way it is like trying to use Ba as a gain factor or slope and the initial pressure as an short term intercept or offset. By getting most of the data points to match up along your ladder, the overall model is better.

I try not to tweak the bullet weight if I actually know it isn't off, but I am willing to tweak initial pressure and powder since I know those are due to the gun and the powder batch or humidity content. YMMV

 

[Laurie]

This practice sounds something like what you've described.

Yes, exactly the same!

 

[SeabeeKen]

Jepp2, you have mentioned adjusting Ba values. I had thought that Ba referred to burning rate, and I see that QL inserts the appropriate values for the powder you have entered. Do you then tweak these from what QL gives you? And, if so, on what basis do you do this?

Ba is where the powder model is calibrated to YOUR rifle and IP would seem to be a pressure spike that varies with seating depth and bullet hardness. A pressure trace system would be the only way to get accurate pressure measurements for IP. Anything else is a guesstimate

 

[mikecr]

QL is internal ballistic software that is just like external ballistic software in one regard: NEVER LIE TO IT
Enter all values correctly, and tweak only the CAUSE of discrepancy.

For example, a fast/slow lot of powder may need a Ba adjustment, but different seating does not change anything about the powder. So don't adjust Ba for seating changes. If you do that and save the powder file, then you have created no more than a bogus powder file.
And when you do a Ba tweak, you should also test that powder in another cartridge. If your new Ba is correct, it will not need further adjustment in another cartridge. Then save the custom powder file for credible use.

For a load-pressure curve needing expansion/collapse, use 'weighting factor'.
Make sure your bullet's shank seating depth is correct (don't use COAL), and your barrel length is correct, and H20 capacity, and if you end up with a ~50fps discrepancy then run it with different QL barrels. YOUR barrel could be a faster/slower barrel with a different cross-sectional bore area. QL was kind enough to provide plenty of bogus barrels (and powders) in their system.. Test barrels & powders from different realms I guess.

 

[BCBRAD]

QL is internal ballistic software that is just like external ballistic software in one regard: NEVER LIE TO IT
Enter all values correctly, and tweak only the CAUSE of discrepancy.

For example, a fast/slow lot of powder may need a Ba adjustment, but different seating does not change anything about the powder. So don't adjust Ba for seating changes. If you do that and save the powder file, then you have created no more than a bogus powder file.
And when you do a Ba tweak, you should also test that powder in another cartridge. If your new Ba is correct, it will not need further adjustment in another cartridge. Then save the custom powder file for credible use.

For a load-pressure curve needing expansion/collapse, use 'weighting factor'.
Make sure your bullet's shank seating depth is correct (don't use COAL), and your barrel length is correct, and H20 capacity, and if you end up with a ~50fps discrepancy then run it with different QL barrels. YOUR barrel could be a faster/slower barrel with a different cross-sectional bore area. QL was kind enough to provide plenty of bogus barrels (and powders) in their system.. Test barrels & powders from different realms I guess.

To add, the Ba changes with pressure it is operated at. Albeit a small amount.

Even a seating depth change, no matter how small, will change the Ba a little.

So, to say this lot of powder has a Ba of 'x' is only accurate in that specific hand load at a that specific pressure. Changing anything will affect the Ba.

 

[mikecr]

The parameters that QuickLoad uses to determine powder burn characteristics are:
1. Heat of Explosion / Potential
2. Ratio of Specific Heats
3. Burning Rate Factor (Ba)
4. Pro or Degressivity Factor a0
5. Progressive Burning Limit z1
6. Factor b
7. Propellant Solid Density
8. Load Density (a calculated factor) @ 100% Fill Ratio

You can tweak Ba, the ambient burn rate (as it sits in it's bottle), but this does not box in the dynamic way powder burns under various pressures.
Would you for example tweak Ba for a charge dropped by 10% weight, or 10% less load density?
Are going to tweak Ba for each increment of your load testing?
NO, you should not, QL does it.