How Case Filling Method Can Alter Powder Column Height
Most of us assume that if we weigh our powder carefully (down to the tenth of a grain or less) we can achieve a uniform powder fill from case to case in our handloads. Weighing does ensure that the weight of the propellant in each case is the same, but is the column of powder the same by volume each time? “Not necessarily” is the answer. An interesting experiment by our friend Boyd Allen demonstrates that the manner in which you place kernels in the case can make a significant difference in the height of the powder column within the brass case.
Using a Gempro 250 scale, Boyd measured exactly 30.6 grains of Vihtavuori N-133 powder. He then inserted this powder in the same cartridge case multiple times. (The case has a fired primer in place.) But here is the key — Boyd used various filling techniques. He did a slow fill, and a fast fill, and he also experimented with tapping and drop tubes. What Boyd discovered was that you can start with the exact same weight of powder (in fact the very same set of kernels), yet end up with vary different fill heights, depending on how you drop the kernels into the case. Look at the photos. Despite variations in lighting, the photos show the same 30.6 grains of powder, placed in the same cartridge, with four different methods.
 |
 |
 |
 |
Boyd Explains the Procedure Used for his Experiment.
EDITOR’s NOTE: So there is no misunderstanding, Boyd started with a weighed 30.6 grain charge. This identical charge was used for ALL four fills. After a fill the powder was dumped from the case into a pan which was then used for the next fill technique to be tried. So, the powder weight was constant. Indeed the exact same kernels (of constant weight and number) were used for each fill.
Boyd writes: “I used the same powder for all fills, 30.6 gr. on a GemPro 250 checked more than once. All fills employed the same RCBS green transparent plastic funnel. The fast drop with the funnel only overflowed when it was removed from the case neck, and 15 granules of powder fell on the white paper that the case was sitting on. The fast-funnel-only drop with tapping, was done with the funnel in place and the case and funnel in one hand, while tapping the case body with the index finger hard, many times (about 20 fast double taps). My idea here was to “max out” the potential of this tapping technique.
The slow drop with the funnel and 10″-long .22 cal. Harrell’s Precision drop tube, was done by holding the scale pan over the funnel and tapping the spout of the pan repeatedly on the inside of the funnel about 1/3 down from the top, with the scale pan tilted just enough so that the powder will just flow. Many taps were involved, again, to max out the technique.
Again, to be clear, after each case filling, the powder was poured from the case back into the scale pan carefully. You may notice the similarity between the fast drop with the drop tube, and the funnel only with tapping. Although I did not photograph it, fast tube drop and tapping (combined) improved on tapping alone, but only to about half as far down the neck as the slow with drop tube. Due to the endless possible permutations, I picked four and left it at that.
I believe that I can make the rough judgment that the scale pan funnel and drop tube technique, which involved a longer drop period, and probably less velocity at the top of the tube, left more room in the top of the case neck than the slow drop from the measure with the same drop tube. You have both pictures, so you can make the comparison.” — Boyd
Does Powder Column Height Variance Make a Difference?
Boyd’s experiment proves pretty conclusively that the method of dropping a given weight of powder can affect the height of the powder column in the case and the degree of powder compression (when a bullet is seated). He showed this to be true even when the exact same set of kernels (of constant weight) was used in repetitive loadings. This raises some interesting questions:
1. Will subsequent cartridge transport and handling cause the powder to settle so the variances in powder column height are diminished?
2. If significant inconsistencies in powder column height remain at time of firing, will the difference in fill level hurt accuracy, or result in a higher extreme spread in velocity?
3. Is there any advantage (beyond increased effective case capacity) for a tight (low level) fill vs. a loose (high level) fill?
We don’t know the answer to these follow up questions. This Editor guesses that, if we tested low-fill-height rounds vs. high-fill-height rounds (all with same true fill quantity by weight), we might see meaningful differences in average velocity. I would also guess that if you fired 10 rounds that exhibited quite a difference in powder column heights, you might see a higher ES/SD than if you shot 10 rounds loaded with a very consistent powder column height (either high or low). But further testing is needed to determine if these predictions are true.
Similar Posts:
- Powder Column Height Varies with Case-Filling Methods
- Advanced Reloading: Controlling Cartridge Powder Column Height
- This May Surprise You — Technique Matters When Case Filling
- Precision Powder Funnels from 21st Century Shooting
- High-Quality Powder Funnels from 21st Century Shooting
Share the post "How Case Filling Method Can Alter Powder Column Height"
Tags: Boyd Allen, Drop Tube, Powder, Powder Column, Reloading
Would the differences in height be as noticeable with another powder, say H4350? As long as the fills where the same for all cartridges at the time of loading, would the eventual results (all else being consistent) be “accurate”? Thanks Carl
Editor: Based on other powder measure testing by Boyd, we think the powder column variances would be MORE dramatic the longer the powder sticks are. H4350 has longer kernels than N-133, so we’d expect the results to be similar… or perhaps more noticeable.
One thing that does come to my mind with a very full case of powder, is bullet movement after seating the bullet. If you don’t use a lot of neck tension the powder column can actually push the bullet upward causing you to have inconsistency in your seating depths. In one of my rifles i have to use very light neck tension and i have to be careful and pay close attention when i drop my powder so i do not get this effect from the full case of powder. Good info Boyd. Thanks for sharing! Lee
I could see this having a positive effect on benchrest but wonder if it would have any effect (perhaps negative)on XTC mag fed rifles where recoil would be put on each round differently, ie; the 5th round in the mag would take 4 recoils, the 4th would take 3 recoils . . .and the 1st round would take no recoil. Just a thought.
I’m thinking that it will settle some in the case between the powder loading, bullet seating and checking/inspection process. For me the 20 + mile truck/car ride to the range will cause more than just the powder to settle.
Interesting info for those that may get to load at a indoor/outdoor range, chamber and shoot.
I can see how this would help with compressed loads, but…
I’m not sure I understand how any of these techniques would achieve greater or worse accuracy? After all, you lay the case on the side when it’s chambered…
In order to use a load, you have to be able to fit the powder in the case in such a way that there is room to seat the bullet. In the example where I dumped the charge into the funnel, with no attempt to slow the filling of the case, not only was there no room to seat a bullet, (since the powder was above the top of the neck), 15 granules of powder fell onto the paper that the case was in the center of when the funnel was removed from the case neck. This is more than a compressed load. Dumping it in, it is impossible.
@queen_stick I was just thinking (or over thinking)of the effects of powder granules being broken and having an effect on the external retardant coating doing its job and also having an effect on the powder column being different (and maybe burn rate efficiency)for each shot with round 1 being compressed and by round 5 the powder column is loose and towards the bottom side, although I doubt it will be drastic it may change a 10 shot ES from single digit to something in the teens.
I known German Salazar would put a loading block of charged cases on the top of his tumbler and vibrate them down that way.
I use a banknote vibrator. Its the same size as a cartridge case block and has a variable speed. It worked quite well with VV N550 in a 223 case and a 80gr JLK @ 100% of case capacity.
ML McPherson did an article regarding this in PS years ago. A swirl charge (if I recall rightly) allowed for charges that were more consistent. Worth a revisit.
When you test for affects of relative load density(what we’re talking about here), be sure to charge cases matched in H20 capacity.
You might also test with a cartridge that’s affected by load density(not a 6PPC). This would be a larger cartridge running rational pressure loads.
My results using a drop tube have not been convincing. But I have had success simply by filling very slowly directly from the pan. Did you try a “Very slow drop with funnel only” Boyd?