June 25th, 2020

Quest for Less Vertical — Six Primer Types Tested at 500 Yards

primer 500 yard testing node vertical H4895 BRA

Do primer types make a significant difference in accuracy or vertical dispersion at long range? The answer is “maybe”. Here’s one anecdotal study that tracked vertical variance among six different primer types. The tester is a good shooter with a very accurate rifle — four of the six 4-shot groups were under 2″ at 500 yards. This test doesn’t settle the question, but does suggest that it may be worth trying a few different primer types with your match ammo.

Here is a very interesting test for the 6 BRA (6mmBR Ackley) cartridge. Forum member James Phillips, a talented long-range benchrest shooter, tested SIX different primer types from three different manufacturers. To help determine vertical dispersion, James set his target out at 500 yards. He then proceeded to shoot 4-shot groups, in order, with each primer type. Velocities were recorded with a chrono. The photo above shows the results. James says: “I’ll retest the best two for accuracy and consistency with 10 shots each”. CLICK HERE for full-screen target photo.

Wheeler 6BR 6mmBR Ackley Improved James Phillips

As you can see, ALL the groups are pretty impressive. The smallest groups, 1.253″, was shot with CCI 400 primers. Next best (and very close) was CCI BR4, at 1.275″ for four shots. The “flat line” winner was the Remington 7.5, at upper left. There was almost no vertical. If you are intrigued by this interesting primer test, you can ask join the discussion in this Primer Test FORUM THREAD.

Primer Brand Group Size Velocity Extreme Spread Std Deviation
Remington 7.5 1.985″ 4 shot 2955 FPS 8 FPS 4.0 FPS
Federal 205M 2.200″ 4 shot 2951 FPS 11 FPS 4.8 FPS
Sellier Bellot SR 1.673″ 4 shot 2950 FPS 14 FPS 5.9 FPS
CCI 450M 2.341″ 4 shot 2947 FPS 14 FPS 6.6 FPS
CCI 400 1.253″ 4 shot 2950 FPS 3 FPS 1.3 FPS
CCI BR4 1.275″ 4 shot 2949 FPS 15 FPS 6.9 FPS

CARTRIDGE: 6mmBR Ackley, aka 6 BRA. Parent case is 6mmBR Norma. The 6 BRA is fire-formed to create a 40-degree shoulder and less body taper. Capacity is increased, but the neck is longer than a 6mm Dasher. The capacity is enough to get to the 2950+ FPS accuracy node. Some shooters say the 6 BRA is more forgiving than the 6mm Dasher. The 6 BRA is certainly easier to fire-form.

LOAD SPEC: 6 BRA (40° 6 BR Improved), 31.1 grains Hodgdon H4895, Bart’s 105gr “Hammer” bullets.

TEST REPORT — Conditions, Shooting Method, Loading Method

Tester James Phillips posted this report in our Shooters’ Forum:
Conditions: The testing was done in the morning over flags. The flags never moved or even twitched. I had as perfect conditions as I could have asked for. It was overcast so no mirage and no wind. There were no other shooters, just me.

Test Procedure: Each shot was precisely shot at my pace and centered the best possible using my Nightforce 15-55X scope. I did not use the round-robin method. Each four-shot group with the same was shot at one time. Then I moved onto the next primer. Everything felt right for each and every shot fired today. Of course I could repeat the test tomorrow and it could be exact opposite of today’s test. We can chase this forever. But [soon] I’m going to test the BR4 and 400 primer… for best accuracy and consistency for 10 shots each.

How Rounds Were Loaded: Each load was weighed to one (1) kernel of powder. So I know that’s as good as I can weigh them. Each bullet seating force was within 1# on my 21st Century hydraulic arbor press.

Previous Initial Load Testing: All groups were shot with 31.1 grains of H4895. During initial load testing I settled in on the Sellier & Bellot primer to finalize everything as it showed more promise over the CCI 450 Magnum I also tried. I was actually surprised to have seen the higher ES and SD from that primer today along with the vertical shown. [Editor: Look carefully — one shot from the CCI 450 is right in the center black diamond, stretching the vertical. By contrast the Rem 7.5 had almost no vertical.]

primer 500 yard testing node vertical H4895 BRA

Velocity and NODE Considerations: I was about 5-6 FPS above what appeared to been my optimum velocity of 2943-2945 FPS, so I’ll test 5 shots of 31.0 and 5 of 31.1 and see what happens from there. I can only assume my velocities where higher due to the higher humidity and of course temps were 5 degrees warmer this morning as well. It wasn’t far off but I noticed it.

Permalink Bullets, Brass, Ammo, Competition, Tech Tip 3 Comments »
March 22nd, 2016

Vertical Fliers? Poor Ignition May Be the Cause…

USAMU Handloading vertical dispersion ignition rimfire accuracy firing pin
Top to bottom – Remington firing pin assembly with ISS, Tubb SpeedLock alloy-composite system without ISS (current versions have dual, opposite-wound springs), and Remington short action firing pin assembly without ISS.

Each Wednesday, the U.S. Army Marksmanship Unit publishes a reloading “how-to” article on the USAMU Facebook page. Last week’s “Handloading Hump Day” article covered mechanical issues and related ignition irregularities that can cause vertical fliers even with good ammunition in an otherwise excellent rifle. We highly recommend you read this article, which offers some important tech tips.

USAMU handloading hump day

Vertical Dispersion: Mechanical/Ignition Issues?

Poor or inconsistent ignition has long been known to be one of the “usual suspects” when one encounters vertical fliers that just shouldn’t be there. By having a sense of some of the basic principles involved, and a few basic areas to check, the shooter may avoid colsiderable frustration, not to mention time, expensive loading components and barrel wear.

USAMU Handloading vertical dispersion ignition rimfire accuracy firing pinIs your well-built rifle of high-quality components plagued with vertical fliers across more than 1-3 handload combinations? Consider the bedding, crown and scope/sight mounts. Are they correct? If so, then you might check for ignition issues before boldly undertaking an extensive, expensive, and quite possibly fruitless quest for the “magic handload”.

SEEING IS BELIEVING: While the author had been aware for many years that poor ignition should be considered and ruled out when dealing with vertical fliers in an otherwise-excellent rifle, actually seeing the problem and its almost instantaneous cure really drove the lesson home.

He was working with a “dot” rifle – a .22 LR match rifle that really stacked bullets into little piles at 50 yards and beyond. With one lot of ELEY Tenex, it produced consistent “bughole” groups at 50, but with another, selected lot of Tenex, similar groups were regularly ruined by single, vertical fliers that did not appear in other rifles. Rather than spending days burning up expensive, select ammunition looking for “magic lots”, he contacted a well-respected rimfire gunsmith and explained the situation.

Without so much as batting an eye, the highly-experienced ‘smith tore into the rifle’s action, and quickly found the cause(s) of the problem. He discovered a demonstrably weak firing pin spring, plus a chip out of the face of the firing pin where it contacted the cartridge rim.

After replacing and tuning the offending parts, the rifle immediately began shooting tiny, bughole groups with the previously “unacceptable” lot of Tenex. Centerfire rifles can also benefit from ensuring positive, consistent ignition. A wise riflesmith is literally worth his weight in gold!

So, what are some issues we as shooters can inspect in our rifles to help determine if ignition woes could be part of our problem? At the club level, ask yourself if that “experienced” Remington, Winchester 70, or even Springfield-based match bolt gun you’re using is still running its’ original 40-80 year-old factory striker spring? If so, a new replacement is cheap insurance against current or future problems. (And BTW, it might be best to stick to the normal, factory-spec spring weight. A super-powerful spring can cause vertical, just as a weak one one can.) Along with that, a routine check for proper firing-pin protrusion is a quick preventive measure that can rule out potential issues.

Other areas to consider are the centering and consistency of the firing pin’s operation in the bolt. Admittedly, with the increasing use of precision-machined custom actions, this is becoming less an issue every day. Below is the firing pin assembly from a custom BAT action:

USAMU Handloading vertical dispersion ignition rimfire accuracy firing pin

However, particularly with factory actions, a very quick and easy check is to remove the bolt, let the firing pin go forward, and look at the firing pin tip through the firing pin hole. Is the tip off-center in the hole, and possibly striking it as it moves forward? Is the hole out-of-round or burred from being struck repeatedly? If so, a trip to the riflesmith is likely in order.

Similarly, machining issues in the bolt/firing pin system can lead to rough and erratic firing pin movement, in which the firing pin drags against an internal surface of the bolt. In high-quality rifles these issues are relatively rare, but not unheard-of, and it takes mere minutes to rule them out. It may be worthwhile to remove the cocking piece/firing pin/spring assembly and look for any unusual gouges, dings, peening, burrs or signs of abnormal wear.

This task is especially easy with Winchester 70s, Springfields, and the similar Mauser 98s, involving little more than the push of a button and unscrewing the cocking piece assembly. This is just one of the many reasons these tried-and-true actions have earned such a loyal following in the field, among hunters who must maintain their rifles away from a shop.

USAMU Handloading vertical dispersion ignition rimfire accuracy firing pin

Particularly with older rifles, watch for and remove excess grease (or even Cosmoline!) from both the firing pin assembly and inside the bolt. This can help improve firing pin speed and consistency. Other bolt-action designs may need a take-down tool or other measures.

As part of this inspection, AFTER ENSURING THE RIFLE IS UNLOADED, slowly cock the rifle, dry-fire, and repeat several times. Listen carefully near the action for inconsistency in the sounds it generates. Does the striker falling make the same sound each time? Do you hear or feel grinding upon operation? If so, where?

Be sure to check the operation of the cocking piece (bolt shroud), firing pin within the bolt shroud, the cocking piece cam and the rear of the bolt body where the cocking piece cam operates. As with our examination for abnormal wear marks discussed above, look for marks indicating roughness or a possible need for light polishing. Then, clean and lightly grease the bearing surfaces while you’re at it.

Remington 700 bolt shroud and cocking cam
Rem 700 bolt cocking cam

These are relatively easy checks that shooters can undertake to perform a preliminary inspection on their own. Other mechanical issues can also cause ignition issues, chiefly centered around the action of the trigger, sear and sear spring. If these are suspected, a trip to an experienced, qualified riflesmith for diagnosis is recommended. We hope you find this information helpful! Join us again next week, and in the meantime, enjoy the shooting sports safely!

Permalink - Articles, Reloading 1 Comment »
April 1st, 2012

Powder Kernel Uniforming for Ultimate Long-Range Accuracy

MFR ScaleSuccessful long-range shooters know that careful weighing of powder charges helps them achieve superior long-range accuracy. By maintaining powder charges within very narrow weight tolerances, hand-loaders can produce ammo with more consistent muzzle velocities from shot to shot. Low Extreme Spread (ES) and Standard Deviation (SD) numbers translate directly to reduced vertical dispersion at very long ranges (although velocity is not the only contributing factor to vertical spread). In pursuit of load weight uniformity, many of our top long-range aces have invested in the latest, high-tech magnetic force restoration (MFR) digital scales (such as the Sartorius GD503). These laboratory-grade MFR scales are extremely stable (with minimal drift) and they can reliably measure to .005 grain, that is five thousandths of a grain. That is less than the weight of one kernel of typical extruded powder. For example, with Varget, there are three to four kernels in one-tenth of one grain of Varget. That means each kernel weighs .025 to .035 grains.

With the capability of modern modern MFR scales to measure less than one-hundreth of a grain, we have a new frontier in precision reloading. You’ll note, in the preceding paragraph, we said that one-tenth of one grain of Varget is three or four kernels. Well, “which is it?” you might ask. The answer is that it might be three, or it might be four, depending on the size of the individual kernels. That’s a disturbing uncertainty that we simply had to accept… until now.

Powder Kernel Uniforming — A Breakthrough
We now have the tools and the methodology to resolve the inherent uncertainty in individual kernel weight. Using the new technique of powder kernel uniforming, first pioneered by German Salazar, we can now, for the first time, ensure that every kernel of powder that goes into a cartridge is virtually the same weight — the same, in fact, within 0.01 grain (one-hundredth of a grain) TOTAL spread.

MFR ScaleFor a reloader looking to achieve “perfect” load weight uniformity, powder kernel uniforming offers the ultimate control over powder weight. The method we devised to uniform individual kernels consists of kernel core-drilling. The propellant we chose for this kernel-uniforming test was a new prototype (not yet commercially available) EuroChemie RL “X” propellant. This was chosen because it offered relatively large, can-shaped kernels that could be drilled relatively easily.

Powder Kernel Uniforming TestCore-Drilling Kernels with Micro Drill-Bits
The center of each kernel was bored out with a micro-drill. But here’s the key. Before drilling, we first weighed each kernel. Then we selected a micro drill bit of appropriate diameter to achieve uniform weights. With the heavier kernels (in the 0.04 gr range) we used a larger micro-bit. With the lighter kernels (in the 0.02 range), we selected a smaller diameter micro-bit that removed less material from the center of the kernel. Obviously, many kernels were ruined while we perfected the drilling process. It required great patience and a very steady hand. But after a few dozen hours of drilling, we had a batch of uniformed kernels that were all within plus or minus .005 grains (.01 grain ES). Now we were ready to do some testing.

Powder Kernel Uniforming Test

Powder Kernel Uniforming TestProof That It Works
All this time-consuming work to drill holes in individual kernels would be pointless, of course, if it did not produce meaningful accuracy gains. The proof, as they say, is “on the target”. We were curious to see if our uniformed powder kernels would out-perform unmodified kernels, so we did some field testing. We prepared two batches of 6mmBR ammo in Lapua brass, with full case prep, and bullet base to ogive sorting (we wanted to eliminate as many variables as possible). Bullets were Lapua 105gr Scenar Ls, which proved to be some of the most consistent projectiles we’ve ever measured.

One set of rounds was loaded with a carefully-weighed charge of unmodified kernels. Case to case charge weight was held to .05 grain (half a tenth uniformity). Then we prepared a second batch of cartridges with uniformed kernels, using the exact same charge weight, also held to .05 grain (half a tenth) tolerances. We took these rounds to the range, and did a “round-robin” test at 800 yards, shooting one of each type in sequence (i.e. one uniformed on right, then one non-uniformed on left) until we had two 10-round groups. The test was done with a rail gun fitted with a 1:8″ twist, 28″ Krieger 0.236″ land barrel. The uniformed-kernel ammo was shot at the right diamond, while the non-uniformed rounds were shot at the left diamond. Conditions were good, so we simply “held center” on every shot. No attempt was made to correct for wind as our primary concern was vertical dispersion.

Powder Kernel Uniforming Test

Ammo with Uniformed Kernels Shows Significantly Less Vertical Dispersion at Long Range
As you can see, the uniformed-kernel ammo out-performed the non-uniformed ammo. The difference is quite clear. The rounds with non-uniformed kernels (on the left) produced a 10-shot group with roughly 3.0 inches of vertical dispersion. On the right, our ammo with uniformed kernels produced a group with 9 of 10 shots showing roughly 1.75 inches of vertical dispersion (we did have one high flier among the uniformed-kernel rounds). Additionally, we had a lower 10-shot ES and SD with the uniformed-kernel ammo. We repeated this test two more times and the results were similar. The targets speak for themselves. If you are looking for ultimate long-range accuracy, powder kernel uniforming is a “new frontier” you may wish to explore. With all other factors held constant, we were able to reduce vertical dispersion by more than an inch at 800 yards by drill-uniforming our NitroChemie powder. That’s huge in the long-range game.

Yes, the kernel-uniforming process is incredibly time-consuming and tedious, and a set of micro-drills is not cheap. We also freely acknowledge that the process may be much less productive with narrow-kernel propellants that are hard to drill. (Also EuroChemie powders are preferred because the burn rate controlling compounds are impregnated throughout the entire kernel — not just the outside.) But the potential for significant accuracy gains is there. We proved that.

Is it worth the huge investment of time to drill your powder kernels? That’s a question each reader must ask himself. But if you know the competitor on the next bench over has uniformed his kernels, can you afford not to do the same? Sometimes the extra effort is worth it, just for the peace of mind you get knowing you’ve done everything possible to achieve “ultimate accuracy”.

Permalink Bullets, Brass, Ammo, Reloading 24 Comments »