Velocity vs POI/POA

arcticcathonda

arcticcathonda

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So little physics question for you precious folks.

Load A: 2900fps muzzle velocity, zeroed at 100 yards
Load B: Unknown muzzle velocity, scope setting uses Load A zero.


Load B prints 1" below the POA. Is it slower or faster than Load A?
 
Same bullet, or different bullet?

Load B could be slower or it could be faster than Load A. It depends on how that rifle's barrel "whips" or moves during firing, and where the muzzle happens to be in this cycle at the time that the bullet exits the muzzle.
 
This seems like a loaded question... mwah, mwah
I'm assuming load B prints 1" below the POA at 100 yards?
Perhaps it is faster and your rifle is only accurate within 2moa?
Perhaps your increase in load changes the initial trajectory due to a different release point in the resonant frequency of the barrel?
Are you asking out of genuine curiosty or trying to nail down unexplained phenomana from personal experience.
Is this a theoretical or practicle question?
Slower bullets have more drop over a given distance than faster bullets (given identical bullets, wind, and atmospheric conditions).
Shot to shot POA will not demonstrate a 1" difference unless you can say that rifle is repeatable within 0.1moa.
A 1" difference in MPI might warrant an explanation.
I'm only replying because there's nothing to do at work and I'm sooooooo bored.
 
Sorry maybe more clarification is needed. I observed this the other day.

Load A is my standard pet load of 140gr Nosler CC over 43.3gr of H4350 at lands.

Load B is a trial Berger 140 VLD load of 43.5r H4350 at lands.

Rifle is 0.3MOA consistent with the pet load and 0.5MOA groups with the Berger VLD.

The question is all three, curiosity, theory and personal experience.

I will shoot it at LR to confirm MV down the road.
 
Did you run 20 of each through a chronograph to confirm the velocities, or are you just assuming from the powder load difference?

In my experience, different makes of bullets have shown drastic velocity differences for the same given powder load.

An interesting question, but Load A Nosler vs. Load B Berger is not a valid comparison.
 
joe.danay said:
Did you run 20 of each through a chronograph to confirm the velocities, or are you just assuming from the powder load difference?

In my experience, different makes of bullets have shown drastic velocity differences for the same given powder load.

An interesting question, but Load A Nosler vs. Load B Berger is not a valid comparison.
Click to expand...

The 2900fps is the average of 100 loads.

What do you mean by a valid comparison? I understand they are completely different, just curious if the velocity could be ascertained (slower or faster) based on trajectories.
 
Ya I think it's possible to work the equation backwards but I'm not sure if ballistic computers will do that... You typically enter the velocity to figure out the trajectory, not the other way around. But it should be mathematically possible.
Without having chrony data for both loads, it's quite possible that the Bergers with 0.2 grains more powder are actually slower than the Noslers.

The previous post mentions harmonics being a bigger factor than velocity. Has anyone seen data on the actual amount a barrel is deflected when a shot is fired? Now I'm curious! Actual deflection would be affected greatly by the rigidity of a barrel.
 
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You could be quite right, may well be with them seated out further the % of filled case capacity is also lower....
joe.danay said:
Ya I think it's possible to work the equation backwards but I'm not sure if ballistic computers will do that... You typically enter the velocity to figure out the trajectory, not the other way. But it should be mathematically possible.
Without having chrony data for both loads, it's quite possible that the Bergers with 0.2 grains more powder are actually slower than the Noslers.
Click to expand...
 
Buckshot70 said:
It depends on barrel harmonics more than velocity.
Click to expand...

It might, it might not...

Have a look at the first graph on this page: http://www.varmintal.com/aflut.htm

Using the largest amount of deflection and asuming that the different loads are exiting the barrels at oppisite extremes of the resonant barrel swing, you could see a height difference of 1.3" at 100 yards.

Using the smallest amount of deflection, you could see as little as 0.1" at 100 yards. Note the chart assumes a downward swing at the time of bullet exit, so I doubled the amounts to account for bullets exiting at opposite extremes of the barrel swing.

So if your rifle has a long, skinny barrel then harmonics could defineately have more affect than velocity.
If your rifle has a short, heavy barrel it's likely that velocity has more effect than harmonics.
 
If everything is the same (barrel, air temp & pressure) except the unknown load, but the BC is the same (ie. same weight, same shape) and we're talking about the bullet passing LOS for the second time, then your velocity is lower for load B, but not by much. 25-50fps difference I'd guess without knowing the BC.
 
That makes sense. My .223 was spitting out V-max bullets about 100 fps faster than the same weight of Speer bullets for the same powder load. So it's completely possible the velocities are different enough despite the similar powder load.
 
Very interesting. With a 24" barrel in M40 contour I was leaning towards velocity. Running both loads in QL should similar speeds, but that is just an educated guess. To be an inch low at 100 yards I would have to guess the velocity is significantly slower.
 
joe.danay said:
Did you run 20 of each through a chronograph to confirm the velocities, or are you just assuming from the powder load difference?

In my experience, different makes of bullets have shown drastic velocity differences for the same given powder load.

An interesting question, but Load A Nosler vs. Load B Berger is not a valid comparison.
Click to expand...
This has been my experience too.
 
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