Quickload and Bullet Jump

[RickKr]

How does one know or define bullet jump in Quickload? I began using Gordon's Reloading Tool a few months back and have now acquired Quickload. There is a direct parameter in GRT for bullet jump, but I cannot figure out where it is or how to define it in QL. It is hard for me to believe that there is not way, so I've looked high and low, far and wide. I assume I just haven't figured it out.

Rick

 

[Straightshooter1]

How does one know or define bullet jump in Quickload? I began using Gordon's Reloading Tool a few months back and have now acquired Quickload. There is a direct parameter in GRT for bullet jump, but I cannot figure out where it is or how to define it in QL. It is hard for me to believe that there is not way, so I've looked high and low, far and wide. I assume I just haven't figured it out.

Rick

QuickLoad has no function for bullet jump. That's probably because bullet jump is such a very small factor, if at all. Jump is constantly changing as the throat erodes, so what's the point? But, QuickLoad does have a function for adjusting Shot Start Pressure for when touching or jamming bullets adjustments, as well as adjusting for different bullet composition that effect bullet engraving. It's the seating depth that's the big issue as it changes the Useable Case Capacity for the powder's performance.

 

[Murray Brook]

I believe the bullet jump is incorporated into their OAL column. It shows a difference in pressure as you change it.

 

[RickKr]

That is very perplexing as it seems bullet jump does affect pressures and velocities as it changes the effective case/combustion volume. And, yes, starting pressure is an adjustable "calibration" factor, as are some others. I think I'm not talking about chasing the lands, as a matter of practice, more knowing what the distance is between the bullet Ogive and lands as an input parameter as a way of defining what the jump is for modeling.

I'm partially going on results I'm seeing using both QL and GRT and changing bullet jump in GRT and partially going on info from the US Army article about how the bullet moves as a result of the primer going, prior to the propellant beginning to burn.

Comparing the same rifle/case/bullet/loads between QL and GRT, with and without jump in GRT, I'm seeing about a 100 fps difference (lower) in muzzle velocity (~3400 vs 3500) and a ~6000 psi change (lower) with bullet jump in GRT vs no bullet jump. These are very similar in both GRT and QL with no jump. (It does take substantially reducing (to unreasonably low levels ~150 psi) starting pressure in QL to get it to agree with GRT in the zero jump condition. Starting pressure in GRT is also fairly low (1000 psi), which is trouble, but I get that it is a calibration factor more than a real number. It is interesting that pressures due to primer ignition in the ARL article were in the 2K-3K psi range.)

What I take from the ARL article is that the bullet moves into the lands with primer ignition, effectively increasing the effective case/combustion volume when the propellant begins to burn. This seems consistent with the change in velocities and pressures I see in GRT with the jump.

 

[mikecr]

I assume I just haven't figured it out.

Thinking about what things are, or what you're doing, is essential with QL.
It's not a reloading manual.

So think about what 'jump' might mean to a powder load, and think about what seating depth might mean to a powder load. Then adjust parameters provided for what you're doing. In this case it's [Shank Seating Depth] and [Shot Starting Pressure].

 

[RickKr]

Thinking about what things are, or what you're doing, is essential with QL.
It's not a reloading manual.

So think about what 'jump' might mean to a powder load, and think about what seating depth might mean to a powder load. Then adjust parameters provided for what you're doing. In this case it's [Shank Seating Depth] and [Shot Starting Pressure].

I think I'm not trying to use it (either QL or GRT) as a reloading manual. I am trying to model my observed velocities using data from my loads and fired cases. More is given in my reply that I just posted, prior to seeing your reply just now. Shank Seating Depth is still a reflection of the case volume with a seated bullet rather than effective case volume with a bullet already moved into the lands by primer ignition, is my perspective.

 

[mikecr]

What I take from the ARL article is that the bullet moves into the lands with primer ignition, effectively increasing the effective case/combustion volume when the propellant begins to burn. This seems consistent with the change in velocities and pressures I see in GRT with the jump.

Every bit of that is dead wrong, and ANYONE testing this across a chronograph will see this.
Our bullets are NOT moving into the lands prior to powder burn.
QuickLoad is correct. I've validated it for decades.

 

[RickKr]

Well, I'm very new to all of this and just trying to understand and learn. Please elaborate. How does chrono data reveal whether or not bullets move prior to powder burn? Is there other information/data that says that bullets do not move? Not trying to poke anyone in the eye, just trying to understand.