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July 9th, 2021

100/200 Group Benchrest Rifles & Loads — The Winning Formula

IBS Group Benchrest Nationals Jeff Stover IBS

The Rifle for Short-Range Benchrest Competition

Hardware Choices: Actions, Stocks, Barrels, Optics and More
Tech Talk by Jeff Stover

This article was prepared by past IBS President Jeff Stover based on results from the 2019 IBS 100/200 Group Nationals held August 12-17, 2019 at the Holton Gun & Bow Club in western Michigan.

Let’s examine the Top Ten rifles from the 2019 IBS Group Nationals in the 10.5-lb Light Varmint Class. We’ll focus on the most popular rifle components — the choices for Actions, Stocks, Barrels, and Scopes.

IBS Group Benchrest Nationals Jeff Stover IBS

IBS short range 100/200 group benchrest
Hall of Famer Jeff Gaidos taking aim at the 2018 IBS Group Nationals. He has a low-profile carbon-fiber stock with a Leupold fixed-power scope.

For some years now, BAT has been the predominant action. This year BAT actions held nearly 100% of the Top Ten places in all the Bag Gun equipment lists. Bruce Thom’s Idaho-crafted actions, except for a couple stray actions in Heavy Bench, swept the top rankings.

IBS Group Benchrest Nationals Jeff Stover IBS

Next, look at barrels. Bartlein or Krieger seem to rule with upstate New York’s venerable Hart barrels as competitive. Shooters tend to go with winners, so Wayne Campbell and Jeff Peinhardt dominate as gunsmiths for the top benchrest shooters.

In stocks there seems to be variety, but there is some commonality. The Scoville and Scarbrough stocks, both Michigan-made, are laminated wood (balsa and other wood) with carbon fiber and wrapped in carbon fiber. The Scoville stock on my 10.5-lb rifle weighs 18 ounces but is full size with a nice long fore-end. Bob Scarbrough makes a very similar product. Both are winners — it’s a choice of Ferrari or Lamborghini. The Roy Hunter and Terry Leonard stocks among these top rifles take a different route to winner’s circle. Both are wood (cedar or other), but super high-tech as they are laminated with carbon fiber. They are beautiful to boot. High-magnification Leupold, March, and Nightforce scopes rule the roost among benchrest optics.

IBS Benchrest rifle stock tuner

IBS benchrest loading table powder

Bullets and Powder

Bullets are important. Really important. A hot bullet gives you “Teen Aggs” and lots of trophies. An average bullet does not. Most of these are 68 grain 6mm boattails. The Peinhardt (StaMoly Precision) bullet is well represented on this list, but some top shooters make their own as you can see. Bullet jackets are likely StaMoly or J4. For powder, nearly everyone shoots Vihtavouri N133 except a few guys running LT30/32 or surplus 8208.

Vihtavuori N 133 N133 powder reloading

IBS Benchrest wailing wall targets

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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 »