April 18th, 2017

Powder Column Height Varies with Case-Filling Methods

powder drop tube

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.

Using funnels with long drop tubes packs kernels more tightly, creating a shorter powder column. That allows you to get more propellant (by weight) into the case.

powder drop tube

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.

Permalink Bullets, Brass, Ammo, Reloading 6 Comments »
April 18th, 2017

Tough Brass — Peterson .308 Win Brass Strong After 32 Firings

Peterson Cartridge Brass .308 Winchester torture test range accuracy IMR 4064 Sierra 155 Palma bullet
Here are five Peterson .308 Win casings after 32 loading/firing cycles (31 at SAAMI max). The brass remained intact, with no cracks. The circles below the shoulders are markings from pressure testing.

This story comes from the Peterson Cartridge website.

Torture Testing Peterson .308 Win Brass — 32 Load Cycles

Recently Peterson’s ballistician had some extra time in his schedule, and asked what he should work on next. He was told, “Just for the heck of it, see how many times you can fire our .308s before you experience failure.” So that’s what he set out to do.

He took five casings out of inventory and loaded them at SAAMI max pressure, which is the pressure we use for all of our longevity testing. It is a hot load, and he did the firing out of Peterson’s Universal Receiver. This way he could measure pressures and velocities each shot. He shot all five, 20 times. (It takes a long time to do that. Load five casings. Shoot five times. Back into the lab to reload, back into the indoor range to shoot, back into the lab, and so forth.)

After 20 firings with no sign of case deterioration, Peterson’s tester asked if he should keep going. “Sure, let’s see how long these can go”, was the reply. So he shot them five more times. Same result. All casings still in good shape. We told him to keep going. He shot each of them six more times. At this point each of the five casings had been fired 31 times. After several days of this the casings were still in good shape but “ballistician fatigue” was setting in. Finally he said, “Let me take these cases to an outdoor range and see how they do for accuracy.” The Peterson team agreed.

Five Shots at 100 Yards after 32 Load Cycles:

Peterson Cartridge Brass .308 Winchester torture test range accuracy IMR 4064 Sierra 155 Palma bullet

For the 32nd firing, the cases were loaded with a somewhat lighter load, and then tested for accuracy. The test rifle was a Tikka T-3 bolt action, with a 20 inch, 1:11″-twist barrel. After 32 firings the primer pockets had opened about 0.002″ (two-thousandths) but were still tight enough for further use. There were no cracks or signs of head separation. The tester put five shots in three holes at 100 yards. The group was 1.5 inches for the five shots, on a somewhat windy day.

Story Tip by EdLongrange. We welcome reader submissions.
Permalink Bullets, Brass, Ammo, Gear Review 9 Comments »
April 18th, 2017

Teaching New Shooters — CMP Training Resources

The CMP (Civilian Marksmanship Program) offers a wide variety of resources for novice shooters and juniors. These materials help novices learn basic marksmanship skills and get started in competition. Some resources can be downloaded from the CMP website, while others are available for purchase from the CMP E-Store. In addition, The CMP maintains a Coaching Resources webpage with dozens of informative articles. Here are some of the CMP articles you can find online:

teaching shooting positions youth junior

Videos

These short marksmanship trainging videos cover the basics of the Kneeling, Standing, and Prone postions. (NOTE: these are live links — videos will launch when you click.)

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Permalink Competition, Shooting Skills No Comments »