Mikecr
Well-Known Member
And my counter;
All powders vary in burn rate due to ever changing load density, confinement, and pressure at any given moment within a barrel.
Powder burn is very sensitive to initial confinement.
Put a 1/3 charge of powder in an open case, load carefully(barrel upward), and on firing you get WUMP...
Now do the same with a fold of toilet paper set on the powder, and you get BOOM.
This is the functioning of cream of wheat fireforming, and brass weight is not a factor in it.
The confinement offered by that paper, tiny as you can imagine, is significant.
The flame front literally bounces off it to light a higher percentage of powder granule surface at a resultant higher rate.
Another confinement test, caused by load density and/or proximity; with loaded cartridges that hold a relatively low load density(case filled to body-shoulder), you can measure a considerable velocity shift, again with no change in brass weight.
Just hand load one with the barrel pointed straight up, carefully lower the gun onto a rest so that the powder stays rearward in the case.
Fire it across a chronograph and note POI.
Then load case with the barrel pointed straight down, carefully raise the gun to a rest so that the powder stays forward in the case.
Fire it across a chronograph and note POI.
You will see velocity higher when powder was lit most rearward in the case.
This is one reason load density is important -beyond getting enough into a case. Load density is really confinement -caused by the powder itself.
Pressure itself affects every powder burn rate, all along the way, from primer ignition to muzzle release.
When you jam a bullet into the lands, you not only increase in pressure before full land engravement, but you speed powder burn RATE to a different position on a burn rate chart. Advantage in this depends on consistency of it, as it changes MV and barrel timing.
This again, can be independent of brass weight.
All powders vary in burn rate due to ever changing load density, confinement, and pressure at any given moment within a barrel.
Powder burn is very sensitive to initial confinement.
Put a 1/3 charge of powder in an open case, load carefully(barrel upward), and on firing you get WUMP...
Now do the same with a fold of toilet paper set on the powder, and you get BOOM.
This is the functioning of cream of wheat fireforming, and brass weight is not a factor in it.
The confinement offered by that paper, tiny as you can imagine, is significant.
The flame front literally bounces off it to light a higher percentage of powder granule surface at a resultant higher rate.
Another confinement test, caused by load density and/or proximity; with loaded cartridges that hold a relatively low load density(case filled to body-shoulder), you can measure a considerable velocity shift, again with no change in brass weight.
Just hand load one with the barrel pointed straight up, carefully lower the gun onto a rest so that the powder stays rearward in the case.
Fire it across a chronograph and note POI.
Then load case with the barrel pointed straight down, carefully raise the gun to a rest so that the powder stays forward in the case.
Fire it across a chronograph and note POI.
You will see velocity higher when powder was lit most rearward in the case.
This is one reason load density is important -beyond getting enough into a case. Load density is really confinement -caused by the powder itself.
Pressure itself affects every powder burn rate, all along the way, from primer ignition to muzzle release.
When you jam a bullet into the lands, you not only increase in pressure before full land engravement, but you speed powder burn RATE to a different position on a burn rate chart. Advantage in this depends on consistency of it, as it changes MV and barrel timing.
This again, can be independent of brass weight.
