Are burn rate and pressure curve synonymous?

[Bart B.]

With all the ways barreled actions are held by their stock and shooter, plus the spread in barrel bore dimensions for a given cartridge across all barrels, a given cartridge load specifics will easily have a 100 fps or more spread in average muzzle velocity across everyone and their barrel.

Best way to test a load for muzzle velocity numbers is bolt the barreled action to a board clamped solid to a bench top. It'll stay fixed in place during bullet's barrel time very repeatable from shot to shot.

Of course, they'll be different when the rifle is shot free recoil or off ones shoulder. That's not a problem with the ammo.

 

[dmoran]

With all the ways barreled actions are held by their stock and shooter, plus the spread in barrel bore dimensions for a given cartridge across all barrels, a given cartridge load specifics will easily have a 100 fps or more spread in average muzzle velocity across everyone and their barrel.

Best way to test a load for muzzle velocity numbers is bolt the barreled action to a board clamped solid to a bench top. It'll stay fixed in place during bullet's barrel time very repeatable from shot to shot.

Of course, they'll be different when the rifle is shot free recoil or off ones shoulder. That's not a problem with the ammo.

After reading your input to how a rifle is held can effect velocity, had me and @tom curious to how much. So this morning while conducting scope tests and fire-forming brass, @tom tested the fallowing 3 rifle holds with 22-shots fired to each position (66-shots total):

22-shot strings velocity averages / 66-shots total (LabRadar)

• 2672-fps - Free-recoil
• 2670-fps - Light hand and shoulder contact
• 2672-fps - Aggressive hand and shoulder contact

Test was conducted using a benchrest rifle: Panda action, Krieger barrel, chambered in 6mmBRA
Thanks @tom for conducting and sharing the data !.!.!
Donovan

 

[Bart B.]

• 2672-fps - Free-recoil

• 2670-fps - Light hand and shoulder contact

• 2672-fps - Aggressive hand and shoulder contact

Thanks for testing. Those number spreads are at the low end in the range I've got from others.

I'm not surprised at those numbers. It happens. Too bad you didn't shoot to get your numbers with it. The observed spread is masked by LabRadar tolerances. The actual numbers may differ if a chrono with tighter specs were used

How much does the scoped rifle weigh?

 

[LHSmith]

I am not surprised by those numbers either.

 

[dmoran]

@Bart B.
Texted @tom for the rifle weight; he replied 13-lbs.

Maybe your not familiar with Labradar, but comparison tests have proven it to be very accurate, repeatable, and technically advanced in comparison to most other chronographs currently available. Wouldn't be surprised if other types of chronographs that your sources used would have worse tolerances. That may have masked there results, more so then would the continues pulsed radar data collected and averaged like does Labradar firmware.

Personally, while I have experienced and seen proof of POI and dispersion variation in relationship to how a rifle is held, balanced, and/or rested, I had never noticed much variation occurring to the velocity like you report. As stated, the curiosity in that is why we wanted to see results of our own tests and our scenario's !.!.!
Donovan