December 13th, 2012

“It Hammers” — Radical Jennings-Stocked F-TR Rig Shoots Great

We recently reported on the new Jennings F-TR stock with integrated bipod. When we first saw this rig we thought, “OK, it looks cool, but how does it shoot?” Well, we had a chance to test a .308 Win F-TR rifle built by Chesebro Rifles using the Jennings stock, Barnard action, and 32″ Bartlein barrel. With the gun on the bench, we first shot a few rounds to confirm zero and test for function.

Then gun-builder Mark Chesebro set the rifle on the shooting mat, opened up a box of Federal 168gr Gold Medal Match (GMM) .308 Win ammo, and got down to business — from the ground. What happened next can only be described as “shock and awe”. Mark nailed three successive groups that left us shaking our heads in amazement. The Jennings stock works. Does it ever. This gun hammers.

All groups were shot from the ground, bipod-supported, with Federal factory GMM ammo.

Mark’s first three-shot group had two shots in one hole, then the third leaked a bit high for a 0.184″ group. Then Mark dialed down 2 MOA elevation, and drilled an astonishing 3-shot .047″ group. (For reference, the black diamond in the orange paster is 1/4″ from point to point.)

I was watching through a Swarovski spotting scope and I saw all three shots track into one hole that just got a little whiter in the middle with each successive round. I yelled out “Stop shooting!” because I wanted to measure the group. It was an easy mid-zero — and honestly it looked like just one bullet hole from a pistol. That is amazing with factory .308 Win ammo, particularly in a barrel throated for 185s, not the 168gr SMKs Federal uses in its Gold Medal Match .308 ammunition.

Mark Chesebro Rifles

After measuring Mark’s 3-shot bughole, we walked back to the firing line and Mark shot a full 5-shot group. This would have been a two-flat, but he flinched a bit and his third shot went a little high to open the group to a 0.233″. Still darn impressive with factory ammo…

Editor’s Comment: This Gun is Ultra-Stable and Tracks Straight Back
I had a chance to shoot the gun from the ground. I can tell you this — the stock design really works. With the wide-track bipod, the gun is incredibly stable. As you’re aiming there is virtually zero horizontal movement in the crosshairs. All you need to do is squeeze the ears to set your vertical Point of Aim and pull the trigger. This thing is one of the easiest guns to shoot accurately (from the ground) that I’ve ever tried. You don’t have to struggle for stability at all — the gun wants to stay dead calm.

With the large, cylindrical Delrin feet placed on a mat, the gun tracks straight back. And there is no hop, no bounce, no roll. In fact, the gun tracked so well that I could see my bullets impact on the paper target. That’s surprising for a .308 Win with no muzzle brake. After a shot I could slide the gun forward and the crosshairs were right where they should be — the only thing I had to do is squeeze the ears to re-set my vertical. All I can tell you is the thing is very easy to shoot well.

I don’t know whether it is because of the forward-angle geometry of the legs, or the Delrin feet, or the properties of the carbon fiber tube that supports the front end, but the gun seems to have more damping than other metal-chassis stocks I’ve tried. Some metal-stocked guns seem to “ring” and transmit a sharp pulse to the shooter. This Jennings stock doesn’t do that — it seems to soak up vibration somehow. And the recoil is very mild, I think because the Delrin feet slow the gun down as they slide back smoothly.

Bottom Line: We came away very, very impressed with this rifle and the Jennings stock. I have never experienced a bipod-equipped rifle (in any caliber) that is easier to aim and hold steady, or which is easier to return to precise point of aim after each shot. And, without question, this is one of the most accurate .308 Win rifles we have ever shot from the ground. And that was with factory ammo, not tuned handloads!

Making a Great Design Even Better
Could the rifle be improved? Yes. While there is some rear elevation adjustment (via an eccentric bag-rider that rotates) we would like to see more rear-end elevation adjustment, so the gun could better adapt to uphill and downhill target placements. Also we’d like to see a higher mounting point for the bag-rider so you could use a taller, beefier rear bag. We discussed these points with Mark Chesebro, and he’s agreed to start prototyping some upgrades. This may include a thumbwheel-adjustable bag-rider (sort of like an upside-down adjustable cheekpiece). At our suggestion, the vertically adjustable bag-rider may be offered in two versions — straight and angled. With an angled bag-rider (i.e. with a slight amount of drop front to rear), you could adjust your vertical point of aim by sliding the gun forward or aft in the rear bag.

We will supplement this test report with more photos and video in a few days. We know you want to see how well it tracks. The video tells the story better than words can…

Permalink Gear Review, Gunsmithing 2 Comments »
December 13th, 2012

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.

Permalink Reloading, Tech Tip 12 Comments »
December 13th, 2012

Target Gift-Wrapping Paper from Creedmoor Sports

Here’s a cool new item for the avid shooters on your Xmas gift list. For this holiday season, Creedmoor Sports has created special package-wrapping paper with target graphics. The unique, heavy-weight gift wrap features Dennis DeMille’s High Power Rifle National Record Target score of 200-20x+100-8x at 200 yards. The 36″ x 24″ sheets are made from 60# stock with a gloss finish. Individual wrapping sheets cost $1.95 or you can buy five sheets for $7.95. This special wrapping paper with bullseye graphics is perfect for gifts to the shooters in your family, or for gifts a club may present to members at year’s end.

Creedmoor Sports Target Gift Wrap

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