Exploring a Theory

[ET]

I don’t need to express my thoughts on what I see with the latest pressure trace but am trying to focus on one area of the pressure cycle being the decline rate.

The additional red line on TG’s provided trace represents a slower decline rate with some remaining pressure and no secondary spike. No secondary spike means no remaining unburned powder.



Now the big question is how to obtain such a trace with a slower declining pressure rate and no unburned powder?
In theory you would need a more accelerated burn of a powder at the declining point of pressure to offset the current acceleration level to the load.

Any thoughts or comments on this theory?
Now I know some of you may well come up with the same answer I have for a possibility. But keep in mind it is only a possibility and should not be jumped at to try until a careful examination is made of this theory. There may be other factors that need to be looked at.


Ed

[edge]

Reverse duplex ? ;D

edge.

[pposey]

less of a slightly faster powder

[Savage Shooter]

I have found only 2 ways to decrease the 2nd spike in this type trace. (provided it IS a burn rate issue).

1. Faster Powder

2. More Powder

Every powders burn rate "quickens" by adding volume. So it can be as simple as more of the same powder, but in this particular case by the high psi indicated adding more powder would not be a viable option.


HOWEVER, I seriously doubt that burn speed is the culprit on this particular trace (knowing this powder and bullet weight combo should be close to 100% burn) so we would have to evaluate other causes.

Some other possible causes are:

Lack of inertial bullet resistance due to lack of weight, poor fit, poor obturation/seal, barrel harmonics, powder to slow to keep up, and other physical.

I then take individual suspects and attempt to evaluate.

i.e. bullet weight in this instance is probably NOT the problem

poor fit may be contributor (poor fit and poor seal are not always the same thing, a bullet that fits poor and be made "fit" if pressure build up is just right to obturate and seal the bullet SOON after ignition).

poor seal likely contributor (lack of bullet friction contributes to lack of inertial resistance as much or more than bullet weight) and is needed for gas seal to allow pressure build to start.

poor or LATE obturation possible contributor (and probably obturation of the late variety is most dangerous of contributors)

barrel whip or harmonics (not likely in this case since bullet appears to still be full inside of barrel)

This is NOT an answer by any means, it is only an example of the thoughts I have when evaluating a trace for load use.

P.S. when you have a deep thought moment think about Edges response of reverse duplex, if built right it has possible solutions to several of the issues I just mentioned.

Reverse duplex has merit!

[pointman]

Having ordered a pac nor 45 and anxiously awaiting it's arrival, I have been reading all of the discussion about these pressure traces. Thanks to all who have taken the time to do this for us.

I think I understand the goal here is to get something close to ET's straight red line.

Now the question and maybe it is a stupid one but that has never stopped me before, what does a centerfire file pressure trace look like? Is it the match to ET's line?

[pposey]

That's a good question, There is lots more room for variance with a center fire though as there is a better bullet to barrel seal.

[edge]

Mar 23, 2011 8:19:34 GMT -5 pointman said:

SNIP.

Now the question and maybe it is a stupid one but that has never stopped me before, what does a centerfire file pressure trace look like? Is it the match to ET's line?

Look here for some different traces:

www.shootingsoftware.com/pressure.htm

edge.

[pposey]

"Here's a classic good load for 6PPC. The only difference between all these traces is the first 3 were seated right on the lands. The last 4 were 30 thousands of an inch off the lands. Note the substantially reduced pressure and overall reduction in energy."

wow scroll down to this section,,, also has some massive secondary pressure spikes below that

[Dave W]

What about a tri-stack? 5gr of booster for ignition, then the primary, then another 5gr of booster to take over later in the cycle?

[Savage Shooter]

Mar 23, 2011 14:08:02 GMT -5 Dave W said:

What about a tri-stack? 5gr of booster for ignition, then the primary, then another 5gr of booster to take over later in the cycle?

I have given a lot of thought to the sequencing also, I am leaning to like Edge stating ending the load with faster burn rate to perhaps keep up better.

I think more and more that the bullet is getting to far out in front of the burn rate on a lot of these problems.

[ET]

Edge

I had no doubt you’d catch this right away as you earlier proposed looking at this concept of reverse duplex.

Savage Shooter like you I try to isolate the variables and their cause & affect and then try to reintegrate them into main event of interior ballistics. This can be mind boggling at times for me.

How I am seeing for what events occur in a pressure trace is first the rise to peak pressure. Here powder burn is accelerated with pressure rise to produce peak pressure. Once the bullet load has gained significant energy for a level of acceleration it simply creates enough volume in the bore for the pressure to start dropping and the powder burn in turn begins to decelerate.

There comes a point the bullet load is no longer accelerating it has to begin a slight deceleration from bore friction. This sort of explains the “Burn Catch-up Term” that is mentioned.
Now the rate of the bullet deceleration in the bore is also influenced by rate of pressure drop. If the rate of pressure drop can be decreased this in turn should help maintain better bullet velocity when it exits the bore.

Now here’s the catch of going this route, is knowing the right ratio for obtaining the desired results with a reverse duplex. The last thing you would want is an amplified secondary spike.
With the current approach of using a duplex the only thing affected is the way peak pressure is developed.

For anyone looking at the red line I’ve added to the pressure trace this is not a true representation of what a reverse duplex would create and was only meant for visual referencing for looking at a possible theory.


Ed

[redspinner3]

Just a tought, dose the barrel sensor show expansion and contraction. how far down the barrel dose the projectile get pushed before it pulls.
could be all wet here.
G.

[savagebrother]

could the secondary's actually be the shock wave returning back thru the barrel ?? it seems to me that the pressure trace style of reading pressures can give some false readings due to the strain gauge being mounted on the outside of the barrel/chamber area. thats why the big guys use a pressure gauge that is mounted in the chamber and reads direct pressure on it. i would like to see there readings as compared to the strain gauges readings. i can tell you from experience that strain gauges can read different pressures just by where you mount them and that they are subject to and pick up stray vibrations - returning shockwaves in a barrel. especially when you look at where and when the secondarys occur. the initial detonation of the powder starts a shock wave that runs the length of the barrel faster than the bullet is moving, and it bounces back and forth a few times before it dissapates.
just my 2cents worth
sb

[ET]

Redspinner3

The basic principle of the barrel sensor is a strain gauge that responds to the expansion of the barrel from resulting pressure in the bore. It does not however indicate the bullets exact position in the bore. It can calculate the exit point of the bullet.

Savagebrother

I won’t dispute what you are saying.
But I can’t fathom multiple shockwaves running back and forth numerous times without the sensor showing some indications of there presence.
Can’t vouch for the gauge placement at this time but know orientation will affect their performance.
I will be the first also to admit this isn’t a perfect system but it does provide enough information as to what is occurring in the bore with pressures.



Ed