Another question on OBT

[BCBRAD]

The acceleration of the bullet within the barrel is not consistent due to the radial pressure wave travelling the length of the barrel thus deformation of the barrel due to this, tight spots will slow the acceleration and loose spots will not slow the acceleration as much.

The bullet travels down the bore in a hurky jerky fashion due to the changing diameter of the bore.

What counts is what's happening at the time of bullet exit.

 

[RonAKA]

The acceleration of the bullet within the barrel is not consistent due to the radial pressure wave travelling the length of the barrel thus deformation of the barrel due to this, tight spots will slow the acceleration and loose spots will not slow the acceleration as much.

The bullet travels down the bore in a hurky jerky fashion due to the changing diameter of the bore.

What counts is what's happening at the time of bullet exit.

Not true. Due to momentum of the bullet the acceleration will be quite smooth. The only little bit of a glitch area will be when the bullet jumps to the lands, when there is a jump in the bullet seating depth.

 

[BCBRAD]

Not true. Due to momentum of the bullet the acceleration will be quite smooth. The only little bit of a glitch area will be when the bullet jumps to the lands, when there is a jump in the bullet seating depth.

Thinking at the macro level here!

 

[BCBRAD]

The acceleration of the bullet within the barrel is not consistent due to the radial pressure wave travelling the length of the barrel thus deformation of the barrel due to this, tight spots will slow the acceleration and loose spots will not slow the acceleration as much.

The bullet travels down the bore in a hurky jerky fashion due to the changing diameter of the bore.

What counts is what's happening at the time of bullet exit.

Again, it is this radial deformation along the barrel length that begets us the heavy/varmint barrel.
The thicker cross section of the barrel resists this radial deformation better.

 

[FeMan]

Think you have it confused, and are actually referring to pressure. Max acceleration takes place after peak pressure, to barrel exit. It is the pressure behind the bullet that "bleeds off" after peak pressure. The bullets continue to accelerate the entire length of the barrel.
Donovan

Technically you are correct sir. Acceleration = Force (i.e. pressure)/mass. Since the mass is constant, the pressure and acceleration are proportional. The bullet continues to accelerate all the way down the barrel but not at a constant rate. That was the point I was trying to make. The acceleration rate will have a curve that is the same shape as the pressure curve. Never zero, but certainly not a straight line.

 

[dmoran]

Technically you are correct sir.........

I can respect that, and agree !.!.!
Kind of misread your other reply until after I had replied back.
Donovan

 

[kvd]

I am curious why QL’s calculated dwell time and the value returned from the two equations given in post #10 are different. Average acceleration is of little importance really and only serves to supply a value to plug into the second equation when solving for time. Whether the acceleration is faster in the first few inches of barrel travel and slower toward the crown or vice versa is maybe food for thought but one thing is undeniable – whatever is going on, if the MV is known and the barrel length is known, then the average acceleration is a fixed number. One cannot vary either the MV or barrel length without changing the average acceleration. By the same token, once average acceleration and MV are known, the average dwell time becomes fixed as changing either MV or average acceleration will affect the calculated dwell time of the bullet in the barrel.

Granted the difference in calculated values is only a few hundred microseconds but apparently that is significant if you are a disciple of OBT. Wondering how QL arrives at their calculated value? What information must be supplied in order for the program to return the dwell time?

Ken

 

[RonAKA]

I am curious why QL’s calculated dwell time and the value returned from the two equations given in post #10 are different. Average acceleration is of little importance really and only serves to supply a value to plug into the second equation when solving for time. Whether the acceleration is faster in the first few inches of barrel travel and slower toward the crown or vice versa is maybe food for thought but one thing is undeniable – whatever is going on, if the MV is known and the barrel length is known, then the average acceleration is a fixed number. One cannot vary either the MV or barrel length without changing the average acceleration. By the same token, once average acceleration and MV are known, the average dwell time becomes fixed as changing either MV or average acceleration will affect the calculated dwell time of the bullet in the barrel.

Granted the difference in calculated values is only a few hundred microseconds but apparently that is significant if you are a disciple of OBT. Wondering how QL arrives at their calculated value? What information must be supplied in order for the program to return the dwell time?

Been nearly 50 years now since I've done any significant amount of calculus. However, I have always found it helpful to look at extremes when trying to understand a concept. Take two cases. First you have a very high acceleration up to full speed in the first 2 inches of the barrel. That takes very little time, and once at full speed it takes very little time to travel the length of the barrel. Total barrel time is quite short. Now consider the other (hypothetical) extreme where the bullet chugs down the barrel at 100 fps and magically in the last two inches accelerates to 3500 fps. Takes a long time to get down that barrel, and even though that last two inches is pretty fast, total time is quite long compared to the first case.

So, my conclusion is that rapid early acceleration (faster powder?) results in a shorter barrel time than later acceleration (slower powder?), even though the barrel length is the same, and the muzzle velocity is the same.

Just my thoughts without having to dig into the heavy math...