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 »
March 29th, 2016

Cactus Classic in Phoenix Draws Top Benchrest Talent

Berger Bullets Cactus Classic Benchrest competition match Phoenix Ben Avery
Click to view full-screen size image.

The Cactus Classic is a prestigious benchrest competition held every year in Phoenix, Arizona. On March 16-20, many of the nation’s top short-range benchresters came to Ben Avery to vie for glory and prizes. There were some impressive performances at this year’s Cactus Classic, hosted by the Arizona Benchrest Shooters. Top Gun was Larry Costa who won the Two-Gun Grand Aggregate as well as the Light Varmint (LV) 200-yard Agg. Lou Murdica (shown below) won the Heavy Varmint (HV) 200-yard Aggregate. At the shorter range, Larry Baggett won the Heavy Varmint 100-yard Aggregate and Gary Bristow won the Light Varmint 100-yard Agg. For full results, click the link below. To see hundreds of high-rez photos from the match, visit the Berger Bullets Flickr Photo Gallery.

CLICK HERE for Complete Cactus Classic Match Results.

HV 200-yard Aggregate winner Lou Murdica.
Berger Bullets Cactus Classic Benchrest competition match Phoenix Ben Avery

Berger Bullets Cactus Classic Benchrest competition match Phoenix Ben Avery

Berger Bullets Cactus Classic Benchrest competition match Phoenix Ben Avery

Most short-range benchrest shooters load at the range.
Berger Bullets Cactus Classic Benchrest competition match Phoenix Ben Avery

Now in his late 80s, Berger Bullets founder Walt Berger is still competing…
Berger Bullets Cactus Classic Benchrest competition match Phoenix Ben Avery

Impressive hardware was on display at the Cactus Classic.
Berger Bullets Cactus Classic Benchrest competition match Phoenix Ben Avery

Cleaning is part of the routine in the short-range benchrest game.
Berger Bullets Cactus Classic Benchrest competition match Phoenix Ben Avery

Permalink Competition, News 2 Comments »
April 24th, 2015

Hammerhead Dual-Caliber, Multi-Discipline Bench Gun

We first ran this story a couple seasons back. Since they we’ve received many questions about this gun, so we thought we’d give readers another chance to learn about this truly innovative, switch-barrel “convertible” rifle. This gun works for both short-range and long-range benchrest matches.

You interested in a really wild, innovative bench gun that can shoot both short-range and long-range matches? Check out Seb Lambang’s latest “do-it-all” rifle. It’s a switch-barrel rifle combining two very different chamberings: 6 PPC and .284 Winchester. With that caliber combo, Seb’s covered from 100 yards (LV/HV mode) all the way out to 1000 (LR Light Gun mode). But the dual chambering is not the rifle’s only trick feature. Exploiting the new long-range benchrest rules, Seb has fitted a 3″-wide, flat rear metal keel to the buttstock. That counter-balances his 30″-long 7mm barrel, improves tracking, and adds stability. Seb built the stock and smithing was done by Australian gunsmith David Kerr.

Seb Lambang 6PPC .284 Win Benchrest hammerhead

Detachable Hammerhead Wing Section Plus Fat-Bottom Keel
To further reduce torque and improve tracking, the stock features an 8″-wide, detachable fore-end fixture. This “hammerhead” fore-end section has extended “wings” on both sides, making the rifle super-stable. The hammerhead unit can be removed, leaving the stock 3″ wide for use in registered benchrest matches where 3″ is the maximum width. The photos below show Seb’s gun in .284 Win Long-Range (LR) Light Gun mode.

Seb Lambang 6PPC .284 Win Benchrest hammerhead

(more…)

Permalink - Articles, Gunsmithing 2 Comments »
October 4th, 2014

Fascinating Test Shows Tuner Settings Can Alter Point of Impact

6PPC Pascal Fischbach Bukys Barrel Tuner sine waveHave a good look at the photos below — this may be one of the most noteworthy target strings we’ve ever published. What you can see is the effect of barrel tuner position on point of impact (POI). You can clearly see that the tuner position alters the up/down POI location in a predictable fashion.

This remarkable 15-shot sequence was shot by French benchrester Pascal Fischbach using his 6 PPC fitted with a CG (Carlito Gonzales) action and a Bukys barrel tuner.

Pascal reports: “After [bullet] seating and load validation, I put the Bukys tuner on, screwing it out 10 turns. According to Carlito, the CG’s super stiff action-to-barrel fit gives a faster vibration modulus that is detrimental below 10 turns [position of the tuner].” Pascal’s procedure was to screw out the tuner 1/4 turn progressively from one shot to the next. He shot one bullet at each tuner position, with a total of 15 shots.

15-Shot Sequence with Tuner Changes
6PPC Pascal Fischbach Bukys Barrel Tuner sine wave
CLICK HERE to SEE Large Version of Complete Test Strip (All 15 shots in a row).

Left Half of Target Strip (shots with 1/4 rotation change of tuner in sequence)
6PPC Pascal Fischbach Bukys Barrel Tuner sine wave

Right Half of Target Strip (shots with 1/4 rotation change of tuner in sequence)
6PPC Pascal Fischbach Bukys Barrel Tuner sine wave

Pascal observed: “Note the point of impact displacement [from shot to shot] tracks clearly along a sinusoide (sine wave curve).” This is indeed notable and significant! This shows how the tuner’s ability to change barrel harmonics can alter the position of the muzzle as each bullet exits, resulting in a higher or lower POI. Pascal sent his results to Carlito Gonzales in Argentina for analysis.

Pascal poses this question to readers: “Guess which three positions Carlito recommends to try?”

Editor’s Note: While this target sequence clearly shows how tuner position can alter bullet point of impact, this, by itself, does not tell us which tuner position(s) are best for accuracy. That will require further multi-shot group testing, involving careful experimentation with tuner position (and powder charge weights). But for those folks who doubt that a tuner can make a difference on a short, fat barrel, just take another look at the photos. The up/down changes are undeniable, and noteworthy in the wave pattern they follow.

6PPC Pascal Fischbach Bukys Barrel Tuner sine wave

Permalink Bullets, Brass, Ammo, Gunsmithing, Tech Tip 6 Comments »
January 26th, 2014

PMA Tool Now Offers High-Quality Carbide Expander Mandrels.

Responding to customer requests, PMA Tool is now offering carbide expander mandrels in popular calibers. These carbide mandrels are listed as .22, .24, .26, .28, and .30 calibers, but they are sized for popular chamberings in .223, .243 (6mm), .264 (6.5mm), .284 (7mm), and .308 (7.62mm). PMA’s new carbide expander mandrels will cost $56.95 per item.

PMA’s tool-makers tell us: “Over the past several months we have received many requests to make expanding mandrels from carbide. Due to this popular demand we are now offering expanding mandrels from carbide. Carbide reduces galling and scratching both on the inside of the case neck and the mandrel itself. We still recommend the use of lubricant when expanding case necks to make the operation easier. These mandrels are ground from a 3/8” solid carbide blank and sized properly to expand case necks, preparing them for neck-turning. They can also be used to iron out dings and flat spots on new brass not destined to be neck turned, preparing them for loading and bullet seating.”

PMA Dual Taper Non-Carbide Expanders are Just $8.95
PMA also makes regular steel expander mandrels at a much lower price — $8.95. These regular Expanding Mandrels are designed to fit both the 21st Century Shooting and Sinclair Expander Dies. PMA states: “Our mandrels are longer than other expanding mandrels and feature a special dual taper which expands both on the up and down stroke of the press to more uniformly expand and straighten case necks.” These regular expanders are offered for all popular calibers, from .17 all the way to .338.

PMA Expander Mandrel steel carbide

PMA Specialized Necking-Up Mandrels for 30 BR and 6 PPC
Last but not least, PMA makes specialized “long-taper” expanders designed to expand 6mmBR brass to 30 BR brass, or expand 220 Russian brass to 6mm (for the 6 PPC). Priced at $9.95, these handy, effective tools make it easy to neck-up your brass for 30BR or 6 PPC.

PMA Expander Mandrel steel carbide

PMA explains: “So you want to make 30BR brass quick? Here’s the mandrel for you. A while back, while forming some 30BR brass for a customer’s rifle we noticed that after necking 6mm up to 30cal the neck fit on the turning mandrel was a lot tighter than we wanted. Regardless of how many steps we took to get there we had to run the case necks over the final expander repeatedly to get the fit right. After that experience we decided to set out and make a mandrel with optimum taper and diameter to neck 6mm up to 30 caliber in one step. We think is the best way to expand the necks of 6BR Lapua brass [for the 30 BR]. Remember to always use plenty of lubricant when necking.”

Product Tip from EdLongrange. We welcome reader submissions.
Permalink New Product, Reloading 2 Comments »
June 1st, 2011

New Lapua 220 Russian Brass — Thicker Necks?

220 Russian brass lapuaJackie Schmidt, posting on Benchrest Central, observed that there may have been some production changes with Lapua 220 Russian brass. This brass is commonly used as the parent case for fire-forming 6 PPC cases. The newer 220 Russian brass has slightly thicker neckwalls, and, according to Jackie, the new brass is more consistent in overall neckwall thickness.

Jackie writes: “I have not made any new PPC cases in a while. But I finally used up all of my older 220 Russian brass, and just bought 500 new cases, in the blue plastic boxes. The necks are thicker. By at least .0008 (eight ten-thousandths). That is right at .0015 on diameter. I am getting neck-wall thickness of .0142″ on the old cases, .0150″ on the new cases. I [fire-formed] two cases, and seated a Flat Base Ultra bullet in each. The old case, with a seated bullet and non-neck-turned case, measures .2708″ average. By contrast, the new case, with a seated bullet in an unturned neck, measures .2722″ average. That is, on average, about .0015 difference in the diameter of a seated round.”

“Anybody else notice this? I guess the main reason I did the measuring is that I am thinking of having a ‘no-neck turn’ reamer ground. With this new brass, .0274″ would be the minimum. The new brass is a tad better in overall [neck]-wall thickness variation.” — Jackie

What does Lapua say? We’ve sent inquiries to Lapua’s USA tech representatives. We hope to have a response soon.

Permalink Bullets, Brass, Ammo 1 Comment »