Last time I posted on observations about the different velocities (or lack thereof) obtained with a "powder back" vs. powder forward position with some low-volume powder charges, I speculated that maybe the sectional density of the bullet was important. Seemed that all the loads we had found which appeared not to be position-sensitive had relatively high sectional-density bullets (a .250 SD 38/55; a .270 SD 30/30; and a .360 SD 43 Mauser), while my low sectional-density loads were showing considerable position sensitivity. So here's what I did: in the 454 Casull case I made up a batch of loads with my lowest SD .452 bullet, a 185 grain Lee using 8.5 grains of Green Dot powder. Then I made the same loading with my highest SD bullet, a 315 grain Lee. Here's what I found today:
Sectional Density = .129
185 grain, powder forward -- 1058 +/- 28 fps
185 grain, powder back -- 1249 +/- 19 fps
Sectional Density = .220
315 grain, powder forward -- 1005 +/- 6 fps
315 grain, powder back -- 1036 +/- 9 fps
Sooo -- huge position sensitivity with the very low SD 185 grain bullet; much much less position sensitivity with the kinda' mid-range SD 315 grain bullet.
I also made some loads with the 8.5 grains Green Dot and the 225 grain bullet I used in previous tests. But this time I stuffed in a wad of dacron to hold the powder back. 1220 +/- 22 fps -- not too good considering the previous "powder back" load had given +/- 14 fps. So my dacron seemed to increase my standard deviation of the load, and as you might guess accuracy was mediocre.
I think I'm learning something.
Velocity change with powder position -- progress maybe
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- earlmck
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Velocity change with powder position -- progress maybe
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is he who heals the most gullies. Patrick Henry
Re: Velocity change with powder position -- progress maybe
This would have a lot more meaning statistically if you shot something like ten each and published the range and average of each load. It takes the "randomness" out of the equation. However, it's a very good subject to investigate. It's difficult to make a statement on a population of 1 data point. Doing more of each will shore up your findings.(Maybe you did do that and didn't share the findings?)
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Re: Velocity change with powder position -- progress maybe
Looks like promising research to me Earl. I'm interested in your finding.
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- earlmck
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Re: Velocity change with powder position -- progress maybe
?? Sorry j... that was average of 5 shots and that little +/- figure? That is one Standard Deviation calculated in Excel spreadsheet.jmiller wrote:This would have a lot more meaning statistically if you shot something like ten each and published the range and average of each load. It takes the "randomness" out of the equation. However, it's a very good subject to investigate. It's difficult to make a statement on a population of 1 data point. Doing more of each will shore up your findings.(Maybe you did do that and didn't share the findings?)
The greatest patriot...
is he who heals the most gullies. Patrick Henry
is he who heals the most gullies. Patrick Henry
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Re: Velocity change with powder position -- progress maybe
OK I'll stick my neck out... Heavy bullets seem to mitigate powder position sensitivity....
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- earlmck
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Re: Velocity change with powder position -- progress maybe
Well, at least heavy-for-caliber. At this point in my little investigation that seems to be the most noticeable difference between those loads that are very position-sensitive and those that are not.Ben_Rumson wrote:OK I'll stick my neck out... Heavy bullets seem to mitigate powder position sensitivity....
The greatest patriot...
is he who heals the most gullies. Patrick Henry
is he who heals the most gullies. Patrick Henry
Re: Velocity change with powder position -- progress maybe
I never did any in depth testing, but I always used pillow stuffing to hold the powder in place in many 454 loads. It did seem to help with consistency over the chrono.