powder charge vs velocity

[LouBoyd]

I'm sure there is a rational reason.
I've never seen, or met anyone who has seen, DECREASING velocity with MORE powder.
The velocities always climbed, and predictably via Quickload.

I have seen this happen. It has nothing to do with a drop in bullet velocity with an increased load. Follow this explanation:
As the load increases the muzzle pressure and muzzle blast increases. The propellant gas released as the bullet clears the muzzle has a considerably higher (molecular) velocity than the bullet and will pass the bullet for some distance. That gas can trigger the first screen of the chronograph prematurely causing the time between the triggering of the first screen and the second screen to be longer. That is interpreted by the chronograph as a lower velocity.

I'd recommend repeating the test exactly as before, but with the chronograph screens set a couple feet further from the muzzle. I'd bet the measured velocity drop goes away and shows normal increasing velocities.

 

[rscott5028]

[...]I commonly see it manifest when averaging erratic extreme spread.

We may not be in such disagreement afterall.

The major difference is that I beleive you're attributing a decrease in MV to the increased powder. But, you just said your hypothetical sample set was erratic. ...which means that one time the mean MV of the load with more powder might be higher and another time lower.

I just don't think it'll consistently average lower MV.

-- richard

 

[jsthntn247]

Bml, what is your barrel length?

 

[BML]

Bml, what is your barrel length?

26" barrel.

 

[brentc]

We may not be in such disagreement afterall.

The major difference is that I beleive you're attributing a decrease in MV to the increased powder. But, you just said your hypothetical sample set was erratic. ...which means that one time the mean MV of the load with more powder might be higher and another time lower.

I just don't think it'll consistently average lower MV.

-- richard

Although it may not always show a consistent drop in MV, it certainly doesn't show a consistent increase. When the data is analyzed it's either a very slight increase or decrease from the previous powder charge, indicating the plateau, or more simply it shows the point of diminishing return where more powder is gaining you very little or no performance increase with the increased pressure and brass wear.

 

[BML]

Here's the complete data for the day's test. These are obviously only 3 shot groups so I realize it's limited data.

50.0g MV:

2981
2977
2799

ES of 22

50.5g MV:

3048
3055
Error-not sure why the error, but that's what the chrono read.

2 shot ES of 7

51.0g MV:

2837
2854
2893

ES of 56


As I've said before, I am pretty new to reloading and while I may have all the data that I need to collect, I'm sure that I am short on the knowledge of how to interpret that data into real world results.

 

[Lefty7mmstw]

I have seen this happen. It has nothing to do with a drop in bullet velocity with an increased load. Follow this explanation:
As the load increases the muzzle pressure and muzzle blast increases. The propellant gas released as the bullet clears the muzzle has a considerably higher (molecular) velocity than the bullet and will pass the bullet for some distance. That gas can trigger the first screen of the chronograph prematurely causing the time between the triggering of the first screen and the second screen to be longer. That is interpreted by the chronograph as a lower velocity.

I'd recommend repeating the test exactly as before, but with the chronograph screens set a couple feet further from the muzzle. I'd bet the measured velocity drop goes away and shows normal increasing velocities.

That can happen at times, but likely it will be noticeably blowing on his chrono. I've litterly blown my chrono over with my 300 ultra and never had it happen, but have seen gas at other times with a chrono. I know it has seen gas because it was registering shots from a gun on the righty side of the bench, and it was MUCH slower than the weapon that made the chrono register. I've also seen bullet shadows and sun glints off of the bullet do some wierd stuff. I'd re-check at a mid-day hour with the chrono back a ways. Powder could be doing something, I'm starting to think lou has the answer and those of us that were looking for phantom load abberations were off kilter.

 

[T3-OleMan]

BML, how far is it from your muzzle to your chrony????? It could be the more powder pushed out is messing with the sensors = miss reads???

 

[jsthntn247]

I would concentrate on 49.5-50.5 if I was you. Either that or find a lower node that will shoot with a better ES. If you are determined to get it over 3000, use another powder, Re 22 or Hybrid 100V will get you there more than likely.

 

[BML]

I set up the chronograph 10 feet from the end of the barrel. I'm not really concerned with reaching a specific speed. Accuracy is most important but I do want to make sure I can maximize my speed without losing any accuracy. If that speed happens to fall in the 2800's somewhere I'm ok with that. If its closer to 3000 that's just an added bonus as far as I'm concerned.

 

[JackinSD]

I set up the chronograph 10 feet from the end of the barrel. I'm not really concerned with reaching a specific speed. Accuracy is most important but I do want to make sure I can maximize my speed without losing any accuracy. If that speed happens to fall in the 2800's somewhere I'm ok with that. If its closer to 3000 that's just an added bonus as far as I'm concerned.

Might want to back that away from the muzzle another 5 to 10 feet. You are definitely getting muzzle blast. That has most definitely been a good portion of your erroneous readings.

 

[rscott5028]

Although it may not always show a consistent drop in MV, it certainly doesn't show a consistent increase. When the data is analyzed it's either a very slight increase or decrease from the previous powder charge, indicating the plateau, or more simply it shows the point of diminishing return where more powder is gaining you very little or no performance increase with the increased pressure and brass wear.

Ageed.

I think diminishing returns (plateau as you put it) was MikeCR's point.

With enough powder, you could start setting your lugs back or experience case head separation which would probably cause a statistically significant decrease in MV provided you live long enough to collect enough samples.

-- richard