velocity goes down with more powder

[jlow]

FWIW, I have seen this plateau then additional increase in speed quite a few times working up load using an Ohler 35P.

 

[madderg]

if you have to much slower powder for a given round, or too much the powder does not stay in the boiler...cartridge, it get thrown out into the barrel. Stay with me here.. as the bullet travel farther down the bore the burning powder has a larger expanding area that it's burning in, and you actually get less pressure, so less velocity. It's like the old slide whistle, same air pressure but as the slide extends the area of the air in the barrel the note continues to get lower...at least to me, that makes sense!!

 

[chkunz]

Did you read #31?

Yes I did but there was a lot there to consider and I am still thinking about it but I think I got hung up on "At the muzzle the condition is released, all is burned and we get a spiking muzzle pressure peak that extends all the way back to the chamber". I will give #31 more thought and see if I can understand and have a meaningful response. The question we are dealing with is why in the case the OP cited would an increase in powder charge result in a decrease in velocity and I am trying to stay focused on that. Thanks for your response.

 

[Frankr]

no it's not a compressed load.
In boyds post #23 the link. i'm I reading it correctly ? it states they shoot 5 shots in a 06 increasing the charge by a half grain per charge. it shows 2,707 for the first shot then 2,794 then 2,814 then up a half grain more to 2,808 then up one more time to 2,818. now did it not go down on shot 4. then what is weird is the pressure is less on shot 5. it looks to me the velocity went down on shot 4. and it was a half grain more powder. now if it was all the same powder charge shots 2 threw 5 the velocity does not look bad. but it looks to me that shot 4 is more powder and less velocity. I'm I wrong?

 

[BoydAllen]

The problems is that we cannot be in the case and barrel so see what is taking place, so we are left guessing, trying to come up with a theory that is consistent with what we do know.

 

[chkunz]

no it's not a compressed load.
In boyds post #23 the link. i'm I reading it correctly ? it states they shoot 5 shots in a 06 increasing the charge by a half grain per charge. it shows 2,707 for the first shot then 2,794 then 2,814 then up a half grain more to 2,808 then up one more time to 2,818. now did it not go down on shot 4. then what is weird is the pressure is less on shot 5. it looks to me the velocity went down on shot 4. and it was a half grain more powder. now if it was all the same powder charge shots 2 threw 5 the velocity does not look bad. but it looks to me that shot 4 is more powder and less velocity. I'm I wrong?

This goes back to my question as to what is the uncertainty (accuracy) of the instrument, the chronograph? Based on the manufacturer's stated specifications of your chronograph (the reference did not shed any light on this) it is at least +/- 15 fps so the apparent decrease is within the variability of the instrumentation. If there is an effect of velocity going down with an increase in powder charge we can not support that conclusion based on this data. I expect the +/- 15 fps stated by the manufacturer is based on the uncertainty (accuracy) of the clock speed and the total uncertainty of the measurement is greater than +/- 15 fps but I do not know that for sure. As I said I do not have much experience with chronographs but do have experience with instrumentation in general.

 

[jlow]

if you have to much slower powder for a given round, or too much the powder does not stay in the boiler...cartridge, it get thrown out into the barrel. Stay with me here.. as the bullet travel farther down the bore the burning powder has a larger expanding area that it's burning in, and you actually get less pressure, so less velocity. It's like the old slide whistle, same air pressure but as the slide extends the area of the air in the barrel the note continues to get lower...at least to me, that makes sense!!

It’s an interesting theory, I was going down the same path except there is a catch and that is after the plateau, the MV goes back up again. That is something that this theory would be hard press to accommodate so there is something else going on in there.

 

[madderg]

if you have to much slower powder for a given round, or too much the powder does not stay in the boiler...cartridge, it get thrown out into the barrel. Stay with me here.. as the bullet travel farther down the bore the burning powder has a larger expanding area that it's burning in, and you actually get less pressure, so less velocity. It's like the old slide whistle, same air pressure but as the slide extends the area of the air in the barrel the note continues to get lower...at least to me, that makes sense!!

It’s an interesting theory, I was going down the same path except there is a catch and that is after the plateau, the MV goes back up again. That is something that this theory would be hard press to accommodate so there is something else going on in there.

When the bullet exits the barrel oxygen is presented to the burning powder, and the pressure goes up.

 

[jlow]

if you have to much slower powder for a given round, or too much the powder does not stay in the boiler...cartridge, it get thrown out into the barrel. Stay with me here.. as the bullet travel farther down the bore the burning powder has a larger expanding area that it's burning in, and you actually get less pressure, so less velocity. It's like the old slide whistle, same air pressure but as the slide extends the area of the air in the barrel the note continues to get lower...at least to me, that makes sense!!

It’s an interesting theory, I was going down the same path except there is a catch and that is after the plateau, the MV goes back up again. That is something that this theory would be hard press to accommodate so there is something else going on in there.

When the bullet exits the barrel oxygen is presented to the burning powder, and the pressure goes up.

I would think once the bullet is out of the barrel, the preverbal plug is gone and pressure cannot go up and certainly can never go higher than when the bullet was still in the barrel.

 

[1adrenaljunkie]

Not discounting anyones experience, but I'm just figuring out how to use my new chrony and I had a similar surprise result. In my case I believe it is a fluke with the instrument since the hotter load had about the expected elevation gain. All this happened while I was doing an Opt. Chrge. Wt. test for .308 win/Nosler 175g hpbt/imr 4064. It happened to be the max load from the Lee chart.

 

[Frankr]

can someone answer my question, in boyds post #23 in the posted link a half grain powder increase the velocity went down 2,814 to 2,808 on shot 4 yes it's only 6 fps but it was a half grain increase in powder. now shots one and two saw a 87 fps gain(sounds right to me). also the pressure went down on shot 4 from shot 3 not what I would think would happen putting a half grain more varget in a 06 case. ??

now as far as chrnoy error's . I will state I have only seen this twice in 18 years of using a chrony. I will shoot 25 shot strings to try to see where my ES really is. where the SD is and the average SD is. in a 25 shot string in a good load I will never see more than 25 fps ES and hope to see under 10 FPS SD and have NERVER! never seen the velocity go down. especially adding a half grain more powder. now I have seen loads have a 150 FPS ES and seeing a errant shot now and then an example would be. 3,025 3,027 3,042 3,215 3,070 . is not uncommon. now if all my reading are 15FPS off so what. I know the load is stable and most importantly under varying temperature condition. I have chrony'ed loads from 95 deg F to -20 deg F the same load in the same rilfe and only lost 50 FPS from 95 down to 0 deg and another 25 fps down to -20. now how accurate is that. sure seems accurate to me and I have used the velocity readings for building drop tables that are sure accurate.(that is my best load) so can the chrony be causeing this to happen. I really do not think so. but im keeping a open mind.

 

[savagedasher]

I think it as the chronograph. Several times I have a slower reading with more powder. I found when testing at 600 yd with a target cam. The Chronograph said the bullet was going slower but the bullet impacted higher on the target at 600. I found the light condition on the chronograph was the problem.
Larry

 

[Jo2]

Not trusting the chronograph sounds a little to me like the guy who flies his plane into the ground in a fog because he couldn't trust his instrument panel. A shot to shot variation in velocity, can, and does occur on a regular basis. As BillPa pointed out in reply #3, he experienced this drop in velocity as he increased powder charge. He reduced the charge, the velocity increased, increased the charge, and the velocity decreased. The results occurred over a one hour period during the same range session. Neither the light nor the temperature were likely to have changed significantly, and if there was a slight change, why did it only occur when he tested the higher charge? In other words, the results were repeatable.

I think that under the circumstances, we can eliminate the chronograph as the weak link in this chain of events. Unfortunately, I am unable to offer any suggestions as to why there is a velocity drop with a powder increase (I have experienced the same thing with H4831 in my 280 Rem).

 

[Syncrowave]

For what it is worth, stoichiometric ratio is the ratio of the oxidizer to the fuel that results in complete combustion. That ratio is different for different fuels and oxidizers. For example oxygen and hydrogen have a stoichiometric ratio of 8.

By mass, yes. By moles, no.

When I said it was 1-to-1, what I meant was that there is enough oxidizer in the powder (or more than enough) for it to reach 100% combustion, even in the absence of atmospheric oxygen.

Since I don't know the chemical formulae for the fuel(s) and oxidizer(s), I can't calculate the stoichiometric ratio by mass or moles. But I think it should be clear what I meant. You don't need any air in the case for the powder to burn completely!

 

[savagedasher]

I think it as the chronograph. Several times I have a slower reading with more powder. I found when testing at 600 yd with a target cam. The Chronograph said the bullet was going slower but the bullet impacted higher on the target at 600. I found the light condition on the chronograph was the problem.
Larry

I DO NOT trust a Chronograph.
No 1 the test was done over a period of time. Here is a few things that cause a Chronograph to change the results you get. Lighting, the angle of the light, heat , voltage , wind, change in temp
gun angle the way the test was taken.. Without a back up.
Here is the way I do my testing . I do 10- 2 shot groups at 600yd with each powder charge with the Chronograph . One bullet with a green marker on it. I shoot one lite then one heavy .10 of each the results will show the back up proof. Larry

 

[Jo2]

Larry, I agree that the angle of the light is a factor in achieving accurate velocity readings, but; I would think that when you get a certain velocity with a given charge of powder and after increasing that powder charge with a resulting drop in velocity, you repeat the original powder charge and get the same velocity as the first load you tried, and you repeat this experiment three times on the same day under the same conditions, you have eliminated the chronograph as the source of the problem.

 

[savagedasher]

Larry, I agree that the angle of the light is a factor in achieving accurate velocity readings, but; I would think that when you get a certain velocity with a given charge of powder and after increasing that powder charge with a resulting drop in velocity, you repeat the original powder charge and get the same velocity as the first load you tried, and you repeat this experiment three times on the same day under the same conditions, you have eliminated the chronograph as the source of the problem.

The only way you can get any real answer you must shot One then the other in the same period of time. First a lite then a heavy and repeat the same 10 times. You can take some of the problems with the crone out. As a back up shoot 300yd plus and look where the bullets impact. With a target cam you can go to 600 Or longer and see the impact in real time. It not what the crony tell you it where the bullet impact at longer distance. Larry

 

[Barlow]

I have been gone a few days and I did not read all the posts. I had the exact same thing happen on the 17th of this month. 25-06 Rem in Ruger 77 TS. 49,5 grs IMR4831, RP cases, WLR's 3055 mv, 50 grs IMR4831 3046 mv, 50.5 gr IMR4831 3110 mv. Used 100 gr Hornady sp in all. I have had this happen before, but can't recall the exact circumstance. The 49.5 gr load was the most accurate load in the Nosler book and three shots went into .561 at 100. IIRC it's a starting load. Barlow