Spearpoint ELR: June 2022 Retrospective

The other weekend I traveled with my 33XC for the first time to Spearpoint Ranch in Barnard, KS to shoot two ELR matches. This weekend was a complete and utter rollercoaster. As an ELR rookie, it was also one of the greatest trial-by-fire learning experiences of my competitive shooting career so far.

What is ELR?

ELR (Extreme Long Range) consists of shooting targets well beyond “typical” ranges for rifles. When exactly distances start becoming “extreme long range” is up to debate, but this match featured targets from 1,510 yd (0.86 mi) to 2,907 yd (1.65 mi).

The main Saturday match consisted of Light and Heavy divisions. Light division included rifles shooting .338 caliber and smaller (max 26lb) while Heavy division included all other calibers up to and including .50 BMG (max 50lb). The Sunday event was a special Rookie match for competitors who’ve shot less than six ELR-type matches and have never placed top 10 in one (limited to .375 CT and smaller).

Both matches began with a single cold bore shot at 1,560 yd followed by three strings of 10 rounds. In each string shooters engaged two targets of known distance – five rounds for target A hit-or-miss followed by five rounds for target B hit-or-miss. Scoring followed King of 2 Miles rules which calculates score based on target distance with multipliers for earlier round impacts.

Match Preparation

140 gr Hybrids getting the job done

I’ve only shot two ELR-style matches before: Nightforce ELR 2021 and ELR Southeast Fall Classic 2021. Both were shot with my 6.5 Creedmoor PRS rifle I was using at the time.

While the 6.5 held its own in Casper, WY with high DA and easy desert spotting conditions, the Fall Classic in Blakely, GA was a completely different story. If I wanted to compete seriously in ELR I needed to up my equipment and up my game.

After months of accumulating components, my 33XC was born:

  • Terminus Zeus action
  • MDT ACC chassis
  • Tangent Theta TT525P scope
  • Spuhr SP-4602 20MOA mount
  • Blake straight 1:9″ twist 32″ barrel
  • TriggerTech Diamond 2-stage
  • ATS XL tuner
  • T4+ Terminator brake
  • Phoenix Precision bipod

My initial load used:

  • 33XC Peterson virgin brass
  • Berger 300 gr Hybrid OTM Tactical bullets
  • H50BMG powder
  • Federal 215M primers

Cases were neck expanded with a PMA Tool carbide expander mandrel, chamfer/deburred with a hand tool, primed with a CPS, charged with an FX-120i + AutoTrickler V4, and seated with David Tubb’s 33XC seating die on a Forster Co-Ax press.

I first broke in the barrel with 50 rounds of the minimum charge, 116 gr H50BMG according to Tubb’s 33XC writeup. Bullets were seated 0.040″ off the lands with a COAL of 4.274″.

With Spearpoint coming up soon, my load development process was very abbreviated. I followed Tubb’s writeup and did a ladder test beginning at 116 gr, incrementing by 2.0 gr until hitting pressure.

My LabRadar was on the fritz during the test, but I captured pressure traces with my PressureTrace II:

Ladder test 116-128 gr H50BMG. T1=116 gr, T7=128 gr.
Absolute pressure numbers are APPROXIMATE and ESTIMATED.

The test stopped at 128 gr when I began experiencing heavy bolt lift. I explored 122 gr further and shot an additional 8 rounds with an average 3,148 fps, ES 38, and SD 13.0.

Now, these ES/SD numbers are… not good. But it was a new barrel, unfamiliar cartridge, and I was still getting the hang of prepping these massive cases. Some of the case necks arrived with gnarly dents and, despite mandreling, would’ve benefited greatly from fireforming. For a first, largely exploratory match it was fine.

Tubb publishes a nominal load of 124 gr H50BMG with 300 gr Berger OTM’s averaging 3,160 fps, so my velocity at 122 gr was precisely in-line and I was feeling good. I wanted to stay on the conservative side to avoid any surprises during the match.

Unfortunately I didn’t have the opportunity to shoot beyond 100 yd paper prior to the match. The only range nearby has steel out to 400 yd, and this rifle would’ve sent those steels into the stratosphere.

I dropped off a batch of cartridges to UPS to ship to Spearpoint, downloaded an Applied Ballistics CDM to my Kestrel, and started packing for the trip.

The problems begin

To uphold the integrity of the cold bore shot, Spearpoint closes its range to competitors the morning of a match. So in order to chrono and confirm zero I made plans to arrive early the day before.

This plan was never meant to be.

My trip began with a 4-hour flight delay. This ate up most of my buffer time, but I was still scheduled to arrive with just enough time.

Rifle check-in at the airport went surprisingly smoothly (for Boston).

Out of paranoia I carry my optics in my carry-on rather than inside my checked case. This has always gone fine, but after arriving in Kansas City I opened my carry-on and was presented with this horrifying image.

At some point my Swarovski BTX 115mm objective was banged into and a chunk was taken out of the bayonet cap. Thankfully there was no damage to the glass itself.

After a 3.5 hour drive I finally arrived into Barnard. Despite the fact that sunset was looming, I made a quick stop to pick up groceries for the weekend before the town closed.

In what has to be the world’s worst timing, this detour was the same moment I received a low tire pressure warning. I pulled into the store, picked up food, and by the time I checked out my tire was completely deflated.

I swapped on the spare tire and… despite best efforts didn’t make it back to the range in time.

I picked up my ammo at the clubhouse, installed my scope back on my rifle, and tried to make a plan for starting an ELR match with no zero.

Match day 1: Catastrophe

I was assigned shooter #19 in the lineup. The morning started around 74°F and creeped up to 100°F by mid-day with clear skies, little mirage, and about 10-20 mph wind. I spent much of the morning meeting people and watching other competitors shoot, watching their spotters, and taking notes about how they communicated.

I was shooting the match alone, so I asked around and found several people willing to spot for me. Their first question was always whether I used mils or MOA, and when I responds mils they breathed a sigh of relief. (This became a recurring pattern throughout the weekend: “Mils or minutes?” “Mils.” “Oh thank GOD.”)

When it was my turn, I set up my LabRadar on the line. The plan was to rely on good spotting of my cold bore shot to “back-calculate” my zero, based on my Kestrel data.

String 1: Cold bore (1,560 yd), T1 (1,510 yd), T2 (1,669 yd)

Off the bat my velocities were significantly lower than expected – a full 20-30 fps lower. I didn’t impact a single target as I grappled with both elevation and windage issues.

Alright, no problem. I told myself. I know what my velocity is now, and at least I’m dialed in closer.

String 2: T3 (1,860 yd), T4 (1,943 yd)

I updated the velocity in my Kestrel to 3,131 fps and subtracted an elevation offset based on my “zeroing.” Rounds started sailing over the targets. The LabRadar reported my velocities were now increasing and becoming more inconsistent. I’d receive a correction to come down in elevation, followed by a call to come down even more, followed by a third call to remove the previous two corrections.

Zero hits.

This second string averaged 3,156 fps and every shot produced heavy bolt lift. This, despite the same exact load with a very similar velocity (3,148 fps) displaying zero pressure signs in testing at home.

Shot #2 clocked in at an abnormally high 3,184 fps before dipping back down to 3,140-3,160 fps for the remainder of the string.

Actual notes from the day

String 3: T5 (2,203 yd), T6 (2,913 yd)

I made a concerted effort in my third string not to let rounds cook in the chamber, in case that was causing issues. But out of the gate my velocities continued increasing. 3,171, 3,190, 3,183, 3,191…

Every round produced heavy bolt lift, this time worse than before. I transitioned to T6, fired a shot, opened my bolt, and… the fired case remained in the chamber.

I cycled the bolt again to no avail. The case failed to extract. I called out to my spotter who jumped in, made sure the rifle was safe, and helped guide a cleaning rod down the muzzle to push the case out. We ensured the bore was clear, I loaded another round, fired, and… another case failed to extract.

I called it there.

I packed up my rifle, removed the bolt, and a chip of metal fell out. My extractor had broken.

In a stroke of (extreme) luck another competitor Justin Wolf was carrying extra M16 extractors with him and performed field surgery on my bolt to get it up and running again.

Back to the drawing board

The day was a complete catastrophe. I spent that evening talking to others, asking opinions, taking notes, and formulating a plan for the Rookie match the next morning. The biggest question on my mind was whether to even continue shooting in the first place.

Once the temperature cooled down, I went out to the zeroing range with another competitor Gee Mann and confirmed my 100 yd zero, as well as DOPE out to 1,400 yd. Gee spotted for me and helped true my Kestrel data once we started making impacts.

I was now making consistent impacts at range, and my numbers were largely lining up with rounds on target. Across 15 shots, my velocity had finally stabilized around 3,192 fps with an SD of 8.0 fps (interestingly, a sizable decrease from its previous 13 fps).

I came to Spearpoint with 79 rounds on my barrel, and the consensus I received was that my barrel had finished speeding up during the match. With that factor sorted out, the only remaining question was how to mitigate pressure.

With no reloading gear available, decreasing the charge weight wasn’t an option so I turned to another variable I could control – temperature.

Match day 2: Redemption

With newfound confidence in my data and a plan in place, I came into the Rookie match with a vengeance.

That morning Gee Mann located a cooler and we filled it with bags of ice. I kept my ammo chilled throughout the day and only removed them when it was my turn to shoot. I was careful to keep the cartridges dry.

String 1: Cold bore (1,560 yd), T1 (1,510 yd), T2 (1,669 yd)

I started with a baseline of 3,190 fps in my Kestrel. My cold bore shot missed low, but I transitioned to T1, held top of plate, and impacted my first two shots. I made a correction and I was dialed in.

I ended string one with 8/11 impacts and a clean on T2:

My first few rounds shot around 3,150 fps but trended back to 3,180-3,200 fps as the chamber heated up and the cartridges warmed back to ambient.

String 2: T3 (1,860 yd), T4 (1,943 yd)

I took note of this velocity pattern going into my second string. Instead of writing down a single number from my Kestrel for each target, I bracketed my velocity between 3,150-3,195 fps. I began the string using my slower velocity DOPE, then as I continued shooting I corrected towards the higher velocity DOPE. This worked surprisingly well.

String two I scored 6/10 impacts:

String 3: T5 (2,203 yd), T6 (2,913 yd)

This was the final string of the weekend and I went in with the same plan.

I took five shots at T5. Five splashes danced around the plate in the dirt. I transitioned to T6.

At the high end of the bracket, my Kestrel calculated 34.00 mils for T6. Shouting over the wind, my spotter called 6 mils of wind left. I dialed to the end of my windage turret, dialed 25.0 mils of elevation, and held over an additional 9.0 mils in my reticle.

Pulled the trigger… 5.3 seconds later my spotter caught the splash. “Come RIGHT 0.4 mils! RUN IT! RUN IT!” I made a correction and fired. I struggled to open the bolt. As I pried it open, I realized my action screw was now loose and my action was wobbling inside my chassis. My spotter frantically called another windage correction.

I took another shot. The LabRadar recorded its highest velocity yet, 3,212 fps, and my bolt locked closed. The round sailed just off the edge of the plate.

I ended my string and the match there. Despite making zero hits this string, my elevation on all three shots at 2,913 yd were spot-on.

And somehow, that all was enough.

With a total score of 41,476 Ko2M points, I took first place at the Spearpoint Rookie match.

Lessons Learned

Like I mentioned, this weekend was one of my greatest learning experiences in competition shooting so far.

  • Understand your rifle, your load, and the conditions you’re shooting in. Err solidly on the side of caution. I didn’t understand the cartridge I was shooting, I didn’t understand my barrel yet, and I didn’t account enough for the extremely high temperatures in Kansas. Factor in a healthy safety margin, not only for what you expect but what you don’t expect.
  • Don’t get flustered when things go wrong. Focus on what the problem is and what’s within your control to address it. Being upset is only a distraction.
  • Bring tools. Bring extra parts. Have a plan for everything that can possibly loosen, break, or fail. Whatever can go wrong inevitably at some point will.
  • Go into each stage with a well-organized plan. Chefs use mise en place to prepare their workspace ahead of time and keep a clear head. Devise a plan so that you’re simply executing, not thinking on the line.
  • Use gear you’re comfortable with. I went into the match with an F-Class rear bag and realized mid-way through I hated it. Without an adjustable bag rider it was difficult to make fine elevation corrections. As soon as I swapped it for a heavy fill PRS bag, I felt more comfortable and stopped fighting against my own gear.
  • Dial your corrections. This was a big change coming from the PRS world where holdovers are common. Dialing allows you to make precise corrections without thinking and line up targets more quickly and precisely with your crosshairs.
  • Efficiency is key. Quicker corrections means quicker shots before conditions can change. Develop economy of movement and practice shooter-spotter communication so you’re not fumbling on the clock.
  • Learn from people smarter than you. Find the experts and experienced shooters you trust, stick by them, and learn as much as you can. Some of the most talented shooters at a match are more than happy to help rookies. Just don’t bother them when they’re getting ready to shoot.

If you handload your ammunition, check out our open source software ChronoPlotter which lets you easily graph and analyze your load development sessions.

How does humidity affect powder?

Table of contents:

You may have heard about a relationship between humidity and bullet velocity either in a book, on a reloading forum, or from a crusty benchrest shooter right after saying they get better ES/SD’s by only using Poland Springs in their wet tumbler.

Humidity is largely discussed as it relates to calculating ballistic solutions, but one relatively unexplored aspect of humidity is the direct effect it has on your powder itself.

Smokeless powder is hygroscopic – that is, it has an affinity for absorbing moisture from the air. Powder can be expected to perform differently if it’s wetter or dryer, which is why precision reloaders have long-recommended storing components at consistent conditions, but little public research has been done to put actual numbers to it.

PDM velocity

I stumbled on the topic of powder humidity almost by accident. In June I flew to Wyoming to compete in Nightforce ELR, where I learned during my Applied Ballistics PDM that my 6.5 Creedmoor load was clocking in a full 54 fps slower than I expected. I chronographed my load at 2,786 fps some months prior with a LabRadar, and a change of this degree was shocking. My stock Tikka barrel wasn’t nearing the end of its life yet with only ~1,400 rounds on it, and while Wyoming’s environmentals are different from Massachusetts (hotter, dryer, higher density altitude) those differences should lend to the load being faster. I wondered if the plane trip somehow had an effect on the ammo, or if maybe I hadn’t fouled my barrel properly leading up to the PDM. After returning home however I loaded a fresh batch of rounds and confirmed this was, in fact, my new velocity and not just a fluke.

After my PDM I had a chance to talk to Bryan Litz about the discrepancy, and he immediately suggested powder humidity could’ve played a role.

Why is it important?

To put it simply:

“[O]nce you break the seal on a jug, that powder starts to acclimate to whatever your environmental, ambient humidity is. …That’ll change a great deal the way that it burns.”

Bryan Litz, Powder Humidity / Temperature Storage

In your reloading you’ve probably come across a smokeless powder burn chart such as this one. While there are a number of ways to characterize powder performance, powders can be generalized and quickly compared according to their overall burn rate. Hodgdon Titewad (pistol powder) burns faster than H4350 (rifle powder) which burns faster than Retumbo (magnum rifle powder).

In his video, Litz continues to explain that moisture content plays a critical role in controlling a powder’s burn rate, and humidity directly influences that moisture content. A powder that’s been dried will burn faster with higher peak pressures, while “wetter” powder burns more slowly with lower pressures.

Powder manufacturers ship their products targeting a specific moisture content (according to the product’s formulation). But the moment the seal is broken that moisture content begins to change. If you live in a region with a year-round humidity similar to factory levels (typically 40-55% RH), or if the conditions in your reloading room are tightly controlled, there may be minimal change. Here in New England however, the ambient humidity swings wildly with the seasons.

Background information

An article simply named “Powder” (alternatively named “All about powder and a little more”) by Sven-Eric Johansson, published in the Norma Reloading Manual: Expanded Edition, is likely the most comprehensive and authoritative research publicly available on the topic. In the article Sven-Eric details the chemical composition, manufacturing process, and numerous other factors that influence the performance of smokeless powders. An entire section is devoted to moisture content – why powder absorbs moisture, the relationship between relative humidity and moisture content, and how it affects the burn rate of various Norma powders. If you don’t already own it, I highly recommend picking up a copy and reading the article for yourself.

The main ingredient in smokeless powder is nitrocellulose, a substance formed by subjecting cellulose (a fibrous material found in plant cell walls) to a complex set of chemical and manufacturing steps.

On page 112 of the manual, Sven-Eric explains:

“[N]itrocellulose is hygroscopic – this means it has the ability to absorb a certain amount of moisture from the surrounding environment; the amount of moisture is related to the relative humidity.

“The moisture content of a powder directly affects the burn rate of the powder – a powder with low moisture content will burn faster than a powder with high moisture content.”

While the exact composition of H4350 is not publicly known, we know it’s a single base powder which means it’s based solely on nitrocellulose. (Double base powders rely on both nitrocellulose and an added percentage of nitroglycerin for propulsion.) Single base powders are commonly 90-98% nitrocellulose by composition.

Adding other substances to the composition like nitroglycerin can reduce a powder’s sensitivity to humidity, making single base powders more sensitive to humidity change than their double base counterparts:

Norma Reloading Manual: Expanded Edition, Page 113

Sven-Eric went on to further measure humidity’s effect on velocity and pressure for a number of Norma powders:

Norma Reloading Manual: Expanded Edition, Page 115

Important takeaways from this testing are that: 1) humidity has a sizable effect on powder performance, and 2) this effect is not perfectly linear.

Powder does not absorb moisture at a constant rate as it’s subjected to different humidities, and these rates can change according to the exact composition of the powder itself. It’s unclear in the article if only two data points were collected for velocity testing, but a clear pattern was observed in humidity having an increased effect on pressure towards the extreme ends of the scale (lower than 40%, higher than 70% RH).

Since the release of this Norma article, little has been published on the topic that can be considered comprehensive.

Vihtavuori in 2018 posted an extremely broad overview of an internal powder test. In 2020, Litz discussed the topic on an episode of the Everyday Sniper Podcast and reported observing velocity swings of up to 200 fps in testing. He followed up with a brief video on powder humidity describing their testing process at Applied Ballistics but did not include numbers. Bolt Action Reloading recently posted a great video testing H4350 and humidity but recognized shortcomings in his own testing process.

I wanted stronger data about humidity’s effect on my own personal reloading. How consistent should my storage conditions be reasonably kept? Exactly what kind of effect can humidity have on my powder’s performance? How much can my load be expected to change when conditions change?

The big questions

I chose to test H4350 since I personally use it in my PRS load. To understand humidity’s effect, we actually need to break it down into two separate questions:

  • How much does H4350 hygroscopically absorb moisture, and to what degree does it affect charge weight?
  • How does moisture absorbed in H4350 affect the powder’s burn performance?

Changing the moisture content of powder can affect a load in several potential ways. Powder with a higher moisture content contains proportionally less propellant by weight, so it stands to reason that 41.50 gr of H4350 conditioned at 90% RH will produce less overall energy and slower velocities than the exact same charge weight at 10% RH.

It’s easy to condition powder to different humidity levels and compare velocities, but a test like this conflates multiple variables and doesn’t provide the full picture we’re looking for. Increased moisture not only makes powder kernels heavier, but the added water also absorbs more energy from the explosion. Without isolating these effects from one another, it’s impossible to tell how much of our velocity change is caused by one or the other.

To address this, I decided to run two experiments in parallel.

Experiment 1

The first experiment reflects the “real life scenario” and shines light on question #1. Say you’ve unsealed a jug of H4350 and over time the jug conditions to a different ambient humidity in the room. How does this affect your charge weight, and how much can your load’s behavior be expected to change overall?

I began by measuring five equal portions of 600.00 gr H4350, weighed on a calibrated, power conditioned, grounded FX-120i scale. Each portion was quickly poured into an airtight Mason jar with a cigar humidor pack, along with a Kestrel DROP D2 to wirelessly monitor the relative humidity inside each jar.

Boveda humidor packs provide two-way humidity control and maintain a specified target % RH within their containers. I used these packs to condition my powder samples – a technique also used by Applied Ballistics in their own testing.

The five jars contained:

  1. 600.00 gr H4350 (control)
  2. 600.00 gr H4350 + desiccant pack
  3. 600.00 gr H4350 + 32% RH humidor pack
  4. 600.00 gr H4350 + 65% RH humidor pack
  5. 600.00 gr H4350 + 84% RH humidor pack
Airtight containers with powder samples, humidor packs, and Kestrel DROPs

Each jar was cranked tight, labelled, and further sealed in a Ziploc bag.

Prepared samples

Temperature and relative humidity were recorded for each sample every 10 minutes by the Kestrel DROPs, which connected to the Kestrel LiNK app via Bluetooth. The samples were stored in my reloading room away from sunlight for a total of 10 days.

Each sample took about 24-48 hours to stabilize to its target humidity, which it then maintained for the remainder of the time.

Additionally, immediately upon unsealing the H4350 jug, a Kestrel DROP was temporarily placed inside the jug itself and measured a factory humidity level of 51.0% RH. Since the manufacturer jug is not hermetically sealed (the reason for this whole test in the first place!) I created a separate “baseline” sample to act as a control for the experiment. This baseline sample contained only H4350 and no humidor pack or desiccant. A minor change was recorded as the sample equalized inside its container around 52-53% RH.

Initial measurements for Experiment 1

At the end of 10 days, the samples were measured:

SampleRelative HumidityTotal WeightWeight Change
Control53.0% RH599.88 grBaseline
Desiccant14.7% RH596.22 gr-3.66 gr (-0.61%)
32% humidor pack34.9% RH598.16 gr-1.72 gr (-0.29%)
65% humidor pack66.5% RH601.34 gr1.46 gr (+0.24%)
84% humidor pack84.0% RH604.68 gr4.80 gr (+0.80%)

These differences seem small at first glance, but placing them in context is where the real story is. These numbers suggest that a 41.50 gr charge dispensed from a H4350 jug conditioned at 34.9% RH would, in actuality, contain the equivalent amount of propellant as a 41.62 gr charge at factory conditions. A 41.50 gr charge dispensed from a jug conditioned at 14.7% RH (say, through the dead of winter) would contain the equivalent amount of propellant as 41.75 gr conditioned at 53.0% RH. Not even factoring the double effect of dryer powder having an increased burn rate as well.

It’s important to note these numbers only represent this specific lot of H4350 I tested. Other lots may contain different formulations or factory moisture levels that decrease or increase this effect.

Experiment 2

The second experiment hones in on question #2 and isolates moisture content as the sole variable. I hoped to answer exactly how much of the change in powder performance was due to moisture alone, rather than a combination of factors.

I followed a similar process to the first experiment but with one important difference. Rather than conditioning bulk amounts of powder, I began by measuring exactly 12 rounds’ worth of powder (41.50 x 12 = 498.00 gr) at factory humidity level. This sample was poured into an airtight Mason jar with a Boveda pack and Kestrel DROP D2, and was repeated for each humidity level tested.

The five jars contained:

  1. 498.00 gr H4350 (control)
  2. 498.00 gr H4350 + desiccant pack
  3. 498.00 gr H4350 + 32% RH humidor pack
  4. 498.00 gr H4350 + 65% RH humidor pack
  5. 498.00 gr H4350 + 84% RH humidor pack

After conditioning, each sample would then be equally divided into 12 rounds regardless of the sample’s new weight. Measuring samples in this way allows us to directly compare the same initial charge weight at different humidities. A sample at 32% RH will contain exactly the same amount of propellant as an 84% RH sample, with moisture content being the only variable.

Initial measurements for Experiment 2

At the end of 10 days, the samples were measured:

SampleRelative HumidityTotal WeightWeight Change
Control52.2% RH497.92 grBaseline
Desiccant16.9% RH494.72 gr-3.20 gr (-0.64%)
32% humidor pack34.9% RH496.46 gr-1.46 gr (-0.29%)
65% humidor pack66.1% RH499.16 gr1.24 gr (+0.25%)
84% humidor pack82.3% RH501.82 gr3.90 gr (+0.78%)

These weight changes (expectedly) line up almost exactly with the ones recorded in Experiment 1.

Performing a linear regression and calculating the y-intercept lets us estimate that the total weight of a completely desiccated sample containing no moisture would be 492.76 gr. This is a 5.16 gr difference from our 497.92 gr baseline, which lets us calculate that H4350 has an approximate 1.04% moisture content. This falls squarely within typical range according to the Norma powder article.

Loading test cartridges

Experiment 1

Twelve rounds from each of the five bulk powder samples (60 in total) were loaded with the following recipe:

  • Powder: 41.50 gr H4350
  • Brass: 3x fired Lapua, 6.5 Creedmoor LRP
  • Primer: CCI BR-2
  • Bullet: 6.5mm Berger 130 gr VLD Target

I wet tumbled the cases, resized with a 6.5 Creedmoor Redding Type S Bushing FL Sizing Die with 0.288″ bushing, shoulder bumped 0.0020″, neck expanded with a 21st Century 0.2625″ mandrel, trickled to the kernel with an FX-120i scale, and seated with a 6.5 Creedmoor Short Action Customs Seating Die to a factory-recommended 2.800″ COAL. Loading was performed on a Forster Co-Ax press. Each powder sample was opened for the minimum amount of time necessary, and I worked to accurately measure, charge, and seat each cartridge as quickly as possible.

Experiment 2

After weighing, each sample was carefully divided into 12 equal portions for a total of 60 rounds:

SampleTotal WeightCharge Weight
Control497.76 gr (497.92)41.48 gr
Desiccant494.64 gr (494.72)41.22 gr
32% humidor pack496.32 gr (496.46)41.36 gr
65% humidor pack498.96 gr (499.16)41.58 gr
84% humidor pack501.60 gr (501.82)41.80 gr
Weights in parentheses include remainder kernels

and loaded with the same recipe and process as Experiment 1:

  • Brass: 3x fired Lapua, 6.5 Creedmoor LRP
  • Primer: CCI BR-2
  • Bullet: 6.5mm Berger 130 gr VLD Target

Since the FX-120i has a resolution of 0.02 gr (approximately a single H4350 kernel), and I wasn’t about to start cutting individual kernels, a small number of kernels were leftover after dividing up each sample. In these cases, the new smaller total weights were recorded and a note was made to scale (by a very minor amount) any necessary calculations to account for the change.

Loading rounds for the 65% humidity sample

With this second batch of cartridges ready, it was time to shoot some dollar bills into a berm.

Live fire testing

I tested using my Tikka T3x CTR with a 24″ factory barrel. The weather at the range was 77°F 62.6% RH with a 1,864 DA according to my Kestrel.

For data collection, I recorded velocities with a LabRadar and chamber pressure with a PressureTrace II.

The PressureTrace system is based on a strain gage installed directly above the chamber. The gage links to a control box, which transmits data via Bluetooth to a PC running software that records the pressure curves.

I began with 10 fouling rounds and ensured everything was recording properly.

Once the barrel cooled down, I then shot the 12 round control group (unconditioned 41.50 gr H4350) from Experiment 1.

To ensure consistency between shot strings, I monitored the temperature of the chamber with a FLIR camera and waited until it reached 90-100°F before continuing testing (approx. 5 minutes).

Monitoring chamber temperature

It’s important to note here that reading #2 (which is immediately adjacent to reading #1) in the FLIR image isn’t actually 81.5°F. Depending on composition, steel barrels can have a relatively low emissivity level which results in inaccurate temperature readings. One way to account for this is to measure a higher emissivity material like electrical tape (or the plastic tape of the strain gage) on the target.

For each string of 12 shots, the PressureTrace II recorded and displayed a pressure curve chart like the ones below. The software limits 10 shots per file, so each string was split across two files.

Live fire results

Experiment 1

Muzzle velocity:

Group Tested# of SamplesStatsAvg. Velocity
52.7% RH (Control)n=11ES 25, SD 8.12,786 fps
14.5% RH (Desiccant)n=10ES 54, SD 15.92,879 fps
34.8% RH (32% humidor pack)n=12ES 29, SD 10.82,838 fps
66.5% RH (65% humidor pack)n=12ES 50, SD 12.42,747 fps
83.5% RH (84% humidor pack)n=12ES 31, SD 9.22,650 fps

Chamber pressure:

Group Tested# of SamplesAvg. PressurePeak Pressure
52.7% RH (Control)n=851,259 PSI52,376 PSI
14.5% RH (Desiccant)n=1054,396 PSI55,027 PSI
34.8% RH (32% humidor pack)n=1252,917 PSI54,000 PSI
66.5% RH (65% humidor pack)n=1250,157 PSI50,711 PSI
83.5% RH (84% humidor pack)n=1248,146 PSI48,921 PSI

Unfortunately one cartridge in the Control group misfired, and two shots in the Desiccant group weren’t recorded on the LabRadar due to acquisition and user errors.

Experiment 2

Muzzle velocity:

Group Tested# of SamplesStatsAvg. Velocity
52.2% RH (Control)n=12ES 45, SD 12.22,790 fps
16.9% RH (Desiccant)n=12ES 20, SD 6.02,861 fps
34.9% RH (32% humidor pack)n=10ES 31, SD 10.22,829 fps
66.1% RH (65% humidor pack)n=12ES 82, SD 20.52,744 fps
82.3% RH (84% humidor pack)n=12ES 25, SD 6.82,669 fps

Chamber pressure:

Group Tested# of SamplesAvg. PressurePeak Pressure
52.2% RH (Control)n=1251,608 PSI52,545 PSI
16.9% RH (Desiccant)n=1254,032 PSI55,193 PSI
34.9% RH (32% humidor pack)n=1252,472 PSI53,332 PSI
66.1% RH (65% humidor pack)n=1250,205 PSI51,544 PSI
82.3% RH (84% humidor pack)n=1249,076 PSI50,030 PSI

Interpreting the results

Experiment 1

At its lowest humidity (14.5% RH), our 41.50 gr H4350 charge clocked in at an average 2,879 fps, peaking at 2,901 fps. Its highest humidity (83.5% RH) saw an average of 2,650 fps with a lowest velocity of 2,635 fps. The entire experiment saw an Extreme Spread of 266 fps.

Between the desiccated and 66.5% samples, a 10% change in RH resulted in a velocity change of about 25.6 fps. Above 66.5%, this effect nearly doubled and a 10% change in RH resulted in a change of about 57 fps.

There’s a similar trend with chamber pressure:

It’s important to note that the numbers observed for chamber pressure are only estimates and should not be referenced to determine the safety of this or similar loads. The PressureTrace II claims to accurately measure the relationship between samples, but correctly calculating absolute chamber pressure can only be achieved with finely calibrated industrial tools.

Experiment 2

Our second experiment largely corroborates our findings from Experiment 1:

However plotting the two velocity datasets on top of each other provides us with additional insight:

Both experiments found nearly identical velocity spreads at factory humidity levels, but as RH became more extreme the results began to diverge. Since Experiment 2 isolates moisture content as the sole variable, any difference between the two results should be attributable only to their difference in charge weight.

For instance, our 41.22 gr sample of 16.9% RH H4350 (conditioned from 41.50 gr) was 18.2 fps slower than our 41.50 gr sample at 14.5% RH. Presuming there isn’t a significant difference in the 2.4% RH spread, that means that at 14.5% RH approximately 71 fps of muzzle velocity change (from baseline) can be attributed to a change in moisture content, while the remaining 18 fps can be attributed to its effect on charge weight.

The same calculation can be applied to the other end of the graph. At 83.5% RH, approximately 121 fps of muzzle velocity change (from baseline) can be attributed to a change in moisture content, while the remaining 19 fps can be attributed to its effect on charge weight.

Closing thoughts

Some takeaways from this experiment:

Humidity has a significant impact on the performance of H4350 and likely rifle (single base) powders in general.

The “effective” charge weight of a load changes depending on powder humidity – by a few tenths of a grain, in our case with H4350.

However the largest impact by far on powder performance is driven by a change in burn rate. Only modifying a charge’s moisture content (while keeping its effective charge weight constant) has almost as much of an effect as moisture content and charge weight combined.

At the extreme ends of the scale, high RH slows down the burn rate of H4350 more significantly than low RH speeds it up.

Don’t “keep your powder dry,” keep it consistent. Store powder in a closed jug, not in a hopper, away from significant environmental changes.

If you can’t control your storage room conditions, consider using a two-way humidity pack inside the powder jug itself. Boveda 49% RH and Integra Boost 55% RH packs may be candidates for H4350.

Drying out powder doesn’t let you achieve “free velocity.” It increases the burn rate, but if you want a faster burning powder then just choose a faster burning powder. Significantly altering moisture content may create unsafe conditions or unwanted side-effects in your load.

There’s a ton of research opportunity in this area. Future researchers may be interested in testing the RH sensitivity of other popular powders, its impact on characteristics like temperature stability, or even its effect on other components like primer ignition.

There’s no way to know for sure what happened with my 6.5 Creedmoor load, however I’d been loading from the same 8lb H4350 jug since the winter. It’s very likely my powder was dryer during load development, then re-hydrated as spring and summer progressed. A 21% change in RH would easily account for the 54 fps change in velocity.

Special thanks to Brian Li and Kaitlin B. for their assistance in designing this experiment and analyzing results.

If you handload your ammunition, check out our open source software ChronoPlotter which lets you easily graph and analyze your load development sessions.

Also consider donating to help cover website costs and fund future experiments like this one. Making purchases using the affiliate links supports the project as well!

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ChronoPlotter v2.1.0

In this version:

  • Added support for manual entry of powder charge data
  • Added experimental support for ShotMarker files (both .tar and .csv files)
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ChronoPlotter v2.0.0

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  • Added support for graphing seating depth data
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