Heat — What a Michigan Summer Does to Ammunition in a Truck

Introduction

Ask anywhere what happens to .22 LR stored in a hot vehicle and you get the same answer: the wax melts. It is a real thing — .22 LR carries its lubricant on the outside of the bullet, so there is wax exposed to the air on every round in the box, and a box that has been hot comes back sticky and full of grit.

That answer is correct and almost entirely beside the point.

⭐ THE FINDING: the wax is the symptom you can see. The propellant is the risk you cannot. And the single largest lever over both is not what is on the bullet — it is which box on the truck the ammunition rides in. The intuitive place, the cab, is the worst place on the vehicle. The DECKED drawer is the best.

That inversion is what this volume is for.

2.1 The number that governs

SAAMI — the Sporting Arms and Ammunition Manufacturers’ Institute — says to avoid exposing ammunition to sustained temperatures above 150 °F, and puts the sane storage band at roughly 55–85 °F.

The mechanism has nothing to do with wax. Smokeless propellant is nitrocellulose, and nitrocellulose decomposes with heat and time. It is a slow, cumulative, one-way process: velocity drifts, consistency degrades, and eventually ignition gets unreliable. Nothing about a polymer coating on the outside of the bullet touches it. A round that has been cooked is cooked whether or not the box looked tidy afterwards.

That is the whole reason to care about location rather than product.

2.2 Why the cab is the worst place on the vehicle

The figure everyone half-remembers — a parked car gaining about 40 °F over ambient in an hour, with most of the rise in the first thirty minutes — comes from measured work on vehicle heat and it is real. On a 90 °F Michigan afternoon that is a ~130 °F cabin, and dashboards run far hotter still; instrumented studies of parked cabins have recorded dash surfaces approaching boiling in high-sun conditions.

🔴 But read the mechanism, because it is what makes the rest of this volume work: that is a greenhouse number. Short-wave solar radiation comes in through the glass, is absorbed by dark interior surfaces, and is re-radiated as long-wave infrared that the glass will not let back out. The cab is hot because it is glazed. The centre console is not a neutral storage box; it is a box inside a solar collector.

So the intuitive place to keep a truck gun’s ammunition — the console, the glovebox, the door pocket — is the one place on the vehicle specifically engineered to trap heat.

2.3 The inversion: the DECKED drawer

A DECKED drawer is an HDPE box inside a steel bed. It has no glazing at all. There is no pane trapping re-radiated infrared, because there is no pane. It sits under its own lid, shaded further by the bed rack above it, thermally coupled to a large steel bed that radiates freely to the sky at night.

It should therefore track ambient plus a modest solar-gain offset, rather than following the cab’s runaway curve. On the same 90 °F day the cab is at 130 °F and climbing, the drawer should be somewhere well below that and holding.

⚠ That is reasoning from the mechanism, not a measurement, and it is labelled as such deliberately. No source consulted has instrumented a truck-bed drawer, and this dive is not going to invent a number for one. What it will do is tell you how to get yours:

Put a $12 min/max thermometer in the drawer and a second one in the centre console. Leave them for one summer week. Read both. That is the entire experiment. It costs less than a box of match ammunition, it settles the question permanently for this truck in this climate, and nobody publishes that number — so it would be the only real one in this dive.

⭐ The practical conclusion holds either way, which is why it is safe to act on now: the drawer cannot be worse than the cab, because the cab has a heat-trapping mechanism the drawer physically lacks. The measurement determines how much better. It cannot flip the sign.

2.4 Three different things heat does, ranked

Popular advice collapses these into one. They are not one, and they have different fixes.

Table 1 — Three different things heat does, ranked

What heat does	How bad	What actually fixes it
Degrades the propellant — cumulative, irreversible, invisible	The real risk. Governs the 150 °F line	Location only. No coating, no container, no desiccant helps
Softens or melts the bullet lubricant — sticky boxes, grit pickup, lube migrating off the bearing surface	Annoying; a fouling and feeding problem, not a safety one	Location, or a polymer-coated bullet
Drives moisture cycling in a sealed container — condensation on the coldest surface	Slow, and it is the cooling half that does it	Desiccant, plus location

🔴 Note what is in the “actually fixes it” column for the row that matters most. Switching to polymer-coated ammunition fixes row two and does nothing whatsoever for row one. It is a genuine improvement to a genuine annoyance, and it is not heat protection. Buying Clean-22 and then leaving it on the dashboard is a worse plan than leaving bulk CCI in the drawer.

2.5 What the polymer coating actually buys

CCI’s Clean-22 replaces the traditional wax with a polymer bullet coating derived from Federal’s Syntech technology, and CCI claims it cuts lead fouling inside a suppressor by 60 to 80 percent.

🔴 The correction that matters for a take-apart can: the coating changes what the fouling is made of, not how much fouling there is. Every round still pushes powder and priming residue ahead of it into the baffle stack. What the polymer removes is the lead fraction — and lead is the part that cements a rimfire baffle stack into a solid object. So the can gets easier to clean, not cleaner for longer. The commonly cited 300–500 round rimfire interval does not move.

That distinction matters more here than it would for most people, because this suppressor is out of production. A can you cannot replace is exactly the one you do not let go long between cleanings on the strength of a marketing figure.

2.6 The counterintuitive bit about lubricant

The instinct is that expensive ammunition must be better in every way. For heat, it is exactly backwards.

ELEY says so in its own words: beeswax-tallow “produces a softer, thicker and stickier lubricant as opposed to pure paraffin,” and it is what goes on the match rounds — Tenex, Match. Paraffin is “a much thinner lubricant [that] remains harder than beeswax at any given temperature,” has the higher melting point, and is what goes on the semi-automatic and recreational rounds — specifically because it does not clog a semi-auto mechanism.

So the ranking for a hot drawer runs:

Polymer-coated (Clean-22) — nothing to soften
Paraffin-lubed bulk and standard velocity (ordinary CCI) — hard wax, higher melt point, chosen for semi-autos
Beeswax-tallow match ammunition (Tenex, SK, Lapua) — the softest, stickiest lube on the shelf

⚠ Popular advice frequently gets this backwards, describing match lubricant as a “greasy liquid oil” that will blow into a suppressor as sludge. It is not an oil; it is a soft wax. But the direction of the correction is the useful part: the most expensive ammunition you can buy is the worst choice for a truck, and the cheap bulk paraffin that everyone apologises for is genuinely more heat-tolerant than the match stuff.

CCI’s paraffin is commonly reported at around a 160 °F melting point. ⚠ That figure is community-sourced rather than published by CCI, and this dive treats it as medium confidence. Taken at face value it puts a ~130 °F cabin below the melt point — the wax goes tacky rather than runs — and puts a dashboard or a black case in open sun above it. Which is, again, an argument about location.

2.7 What the desiccant is actually for

This is the part that is almost always explained wrong, and getting it right changes how much desiccant you need by two orders of magnitude.

In a sealed bottle, the absolute amount of water is fixed. Heating the bottle adds no water to it. What heating and cooling do is move the relative humidity: as the drawer cools overnight, the air’s capacity to hold water falls, RH climbs, and if it reaches the dew point, liquid water forms on the coldest surface available — the bottle wall, which is exactly where the cartridges are resting.

⭐ So the desiccant is not fighting Michigan’s humidity. It is fighting the nightly downswing of your own drawer. It is a thermal-cycling countermeasure, which is why it belongs in the same volume as the location decision rather than in a general storage checklist.

And the sealed-in air is almost nothing:

Table 2 — And the sealed-in air is almost nothing


Void air in a filled 355 mL bottle	≈ 150 mL
Water it holds at 90 °F / 80% RH	≈ 4–5 mg
Capacity of a single 1 g silica gel packet	≈ 300 mg

A single gram would handle the sealed-in air roughly a hundred times over. So the fill is never the load. What the load is depends entirely on the closure, and that is what decides how much gel to use:

With a poor closure — a beverage cap, a snap latch, a printed thread — the load is leakage. The container breathes as it heats and cools, and each breath brings in outside air. Size for the leak.
With a real gasket — a mil-spec can, a proper dry box — leakage effectively stops, and the load becomes openings. Every time the lid comes off, the whole void volume is replaced with ambient air. Size for how often you open it.

⭐ That distinction is what makes the architecture in the next section worth adopting, because it moves the problem from a leak you cannot control to an event you can count.

2.8 Which desiccant

Orange indicating silica gel, in a sealed packet or a vented canister — never loose beads.

2.8.1 The actual number, worked out

⭐ Two 10 g indicating packets — call it 20–25 g total — in the Sheffield 12633. Here is the arithmetic, because the intuitive answer is far too much:

Table 3 — ⭐ Two 10 g indicating packets — call it 20–25 g total — in the Sheffield 12633. Here is the arithmetic, because the intuitive answer is far too much


Sheffield internal volume	225 in³ = 3.7 L
Less contents (ammunition boxes, magazines, foam)	void ≈ 2.2 L
Water in 2.2 L of air at 90 °F / 80% RH	≈ 59 mg
Working capacity of silica gel (moderate RH)	≈ 150–200 mg per gram
So 1 g covers	≈ 3 lid-openings
20 g covers	⭐ ≈ 55–60 openings before it needs an oven

Every opening is a full recharge of the load — the whole void is replaced with ambient air — which is why openings, not leakage, are the thing to size against once the lid is decent.

⚠ This revises the earlier “25–50 g” figure downward, and for a good reason: that range was sized for an unknown void with a cloth in it. With the box known and closed-cell foam instead of cloth, 20–25 g is generous.

⭐ Use two smaller packets rather than one large one. One at each end reads at a glance, and you can rotate one through the oven while the other keeps working.

⚠ Check the packet is vapour-permeable. Tyvek and paper packets breathe, which is the point. A packet sealed in solid poly film cannot adsorb anything and is decoration.

🔴 And keep hygroscopic material out of the box entirely — see vol 4 on cartons. Paperboard holds roughly 6–7% of its weight in water and will consume this whole charge on its own.

Rule out clay first — it is the actual trap. Most cheap bulk desiccant is montmorillonite clay, and clay gives moisture back into the container as the temperature rises. In a box that heats every afternoon and cools every night, clay would spend the day re-humidifying what it dried overnight. It is the one option that is actively wrong for this application, and it is the one most likely to arrive if you buy the cheapest packets available.

Molecular sieve is technically the best performer in heat — it holds water far more strongly at elevated temperature, and in thermal-desorption testing a 3A sieve gave up only about 40 percent of its moisture by 125 °C while silica gel had released most of its own. That strength is also the problem: it cannot be reliably regenerated in a domestic oven. You would be buying consumables forever.

Silica gel is the right pick here. It works steadily across a wide range, is suited to environments up to about 120 °F, and regenerates at 250–300 °F for one to two hours — an ordinary kitchen oven does that, indefinitely, for free.

🔴 Orange, not blue. Blue indicating gel is coloured with cobalt(II) chloride, classified as a Category 2 carcinogen, restricted in Europe and banned from consumer products in a number of countries. Orange indicating gel uses methyl violet and goes bright orange → yellow → green as it loads. Given a clear bottle, that colour is the entire reason the container choice is a good one: you read the state of the desiccant without ever breaking the seal.

🔴 Never loose beads. One bead into a chamber or a rotary magazine is a malfunction at the worst moment. Sealed Tyvek packets or a vented rigid canister only.

⚠ Check the packet physically fits the neck before buying twenty of them. A flat 5 g packet runs roughly 40 × 55 mm and may not pass a bottle mouth; the small cylindrical canisters sold for pill bottles go in easily.

2.9 Split the jobs — the architecture this dive actually recommends

The single-container plan asked one object to solve two unrelated problems, and it solved neither cleanly. Abrasion control and moisture control are different problems with different right answers.

The abrasion problem is real. A .22 LR bullet is soft lead with an exposed, lubricated bearing surface and a thin, fragile rim — which is why ELEY packs match ammunition in moulded trays so the noses never touch anything, a detail the .22 Rimfire dive already records in its manufacturing volume. Hours of washboard road in a loose container deform noses, burnish lubricant off bearing surfaces, and — on polymer-coated bullets — chip the coating you are specifically paying for.

⭐ So: an indexed inner container for abrasion, inside one gasketed outer container for moisture.

Table 4 — Split the jobs — the architecture this dive actually recommends

Layer	Job	What it must be
Inner — capsules or trays	Abrasion only	Indexed, so rounds never touch each other. Rigid at drawer temperature. 🔴 Deliberately NOT sealed
Outer — ammo can or dry box	Moisture only	A real gasket. One desiccant charge for the whole volume

🔴 THE COUNTERINTUITIVE PART, AND THE ONE THAT IS EASY TO GET WRONG: the inner capsules must not seal. The instinct is to seal everything. A sealed capsule sitting inside a desiccated can is a desiccant-proof pocket — the gel cannot reach the air the cartridges are actually resting in, and you have carefully protected the rounds from the only thing protecting them. Vent the capsules, or use loose-fitting lids. The gasket belongs on the outer box and nowhere else.

2.9.1 The simplification: the factory box already is the inner container

The first version of this section assumed printed PETG trays. Having worked the numbers, that is effort spent on a problem the factory has already solved.

⭐ Abrasion is driven by free volume, and a full rigid factory box has almost none. It is also, by definition, the container the ammunition survived its trip from Idaho in. ✅ And a factory box does not seal — which satisfies the “inner must not seal” rule for free, with nothing to design and nothing to fit.

🔴 But only in plastic packaging, and this is where the ammunition choice was actually decided. The 200-round Clean-22 Suppressor load ships in a carton, and paperboard holds roughly 6–7% of its weight in water — a desiccant load in grams, against a gel charge whose whole working capacity is grams. A carton in this box would leave the gel drying paper for the life of the system. Vol 4 works the trade through; the outcome is Clean-22 Sub-Sonic in its 100-round plastic box, two boxes to a 200-round load-out.

⭐ Which means the plastic factory box is doing three jobs at once, for free: it is rigid (abrasion), it does not seal (the gel can reach the rounds), and it is not hygroscopic (it adds no desiccant load). Nothing needs to be printed, bought, or modified.

⚠ PETG would still be the right filament if trays were being made — glass transition around 80 °C / 176 °F, comfortably above anything an unglazed bed drawer reaches, where PLA’s is roughly 55–60 °C / 131–140 °F, inside the range a vehicle enclosure genuinely hits. 🔴 A stack is load-bearing, and PLA under sustained compression above its glass transition does not shatter — it creeps, and you find out when the lids stop seating. That comparison is kept here because it governs any printed part that lives in this drawer, not just ammunition trays.

2.9.2 The outer box, and the void problem it creates

The box chosen is a Sheffield 12633 .30 cal field box — polymer, stackable, lockable, with a compression-fit lid rated water and dust resistant. Internal volume is 9⅜ × 4 × 6 in, about 225 in³.

⚠ Note what that closure is and is not. A compression-fit lid is a long way better than a beverage cap and a long way short of a mil-spec O-ring. Size the desiccant for a moderate closure, and let the indicating colour tell you how it is actually doing rather than trusting the marketing word “resistant.”

✅ The owner’s worry that a plastic box “may not hold up well filled with ammo” does not apply at this load-out. A .30 cal box filled with centrefire would be genuinely heavy; 200 rounds of .22 LR is about 1.6 lb. The box is nowhere near its limit. The problem is the opposite one:

🔴 A 200-round factory box occupies roughly a tenth of 225 in³. The load-out is about 90 percent air. That is a lot of void to slosh in, and it is also a lot of air for the desiccant to keep dry.

Fill it deliberately — with the right things:

✅ Spare magazines belong in here. The .22 Rimfire dive calls the rotary magazine “the one part whose loss ends the trip”; keeping spares with the ammunition is both good void-fill and good practice. Polymer and steel, no moisture concern.
⭐ Closed-cell foam is the best bulk filler. It absorbs essentially nothing, and it damps vibration — which is the actual abrasion mechanism, so it is doing two jobs.
🔴 Microfiber cloths carry moisture, and that is worth knowing before you seal them in. Synthetic microfibre has low but non-zero moisture regain, and a cloth at room equilibrium can hold a few hundred milligrams of water — comparable to the entire air load in the box. The desiccant then spends its capacity drying the cloth before it gets to the air. If you want a cloth in there for its field utility, dry it in the same oven session as the silica gel. For pure void-fill, foam is strictly better.

2.9.3 Why the steel can was rejected — and the one point in its favour

🔴 On payload, steel loses. A surplus M2A1 (.50 cal) is about 5.2 lb empty, an M19A1 (.30 cal) about 3.7 lb — before a single round goes in. Against a build vol 1 shows is already 114 lb over its label, that is real weight for a box living inside a DECKED drawer that is already the protection.

✅ But steel has one genuine advantage worth recording, because it cuts against the recommendation: thermal mass. The thing the desiccant fights is the nightly cooling swing, and a heavy steel can damps the amplitude of that swing in a way a thin polymer box does not. It is a smaller effect than the location decision and it costs two to four pounds, so the polymer box still wins here — but the trade is real and it is not purely sentimental.

2.10 The recommendation

Ammunition lives in the DECKED drawer. Never the console, never the glovebox, never the dash. This decision dominates all the others.
Leave the rounds in the factory box. It is rigid, it is full, and it does not seal — which is exactly what the inner layer should be. Nothing to print.
One gasketed outer box — the Sheffield 12633 — doing moisture and nothing else.
Fill the void on purpose: spare magazines and closed-cell foam. 🔴 Oven-dry any cloth that goes in.
Two 10 g orange indicating silica gel packets — one at each end, so the colour reads at a glance and one can go to the oven while the other works. Never loose beads. Never cardboard in the box.
Seal it on a dry day, not after a rainstorm with the tailgate open. You are sealing in whatever air is there.
Read the colour when you open it. Orange is fine; green means an oven at 250–300 °F for an hour or two.
Two min/max thermometers, one week, drawer and console. Then come back and fill in the number this volume left open.
Rotate. Heat damage is cumulative and invisible; shooting the truck stock down each season removes the question entirely.

⭐ What this architecture is worth noting for: it ended up requiring nothing to be manufactured. The abrasion problem was solved by not decanting the ammunition, and the moisture problem by one box and a handful of gel. The first plan — bottles — and the second plan — printed trays — were both more work than the problem needed.

References

SAAMI — sporting ammunition storage guidance; avoid sustained exposure above 150 °F; recommended band roughly 55–85 °F. Nitrocellulose propellant degrades cumulatively with heat.
Measured parked-vehicle heating — approximately 40 °F rise over ambient in one hour, most of it in the first thirty minutes; instrumented cabin studies record far higher dashboard surface temperatures. The mechanism is glazing trapping re-radiated infrared.
CCI Clean-22 — polymer bullet coating replacing wax, derived from Federal Syntech; CCI claims 60–80% reduction in lead fouling inside a suppressor. The claim is CCI’s own and is presented here as a manufacturer claim.
ELEY, “Waxing lyrical about .22LR lubricants: beeswax or paraffin wax?” — beeswax-tallow is “softer, thicker and stickier,” used in match rounds; paraffin is “much thinner… remains harder than beeswax at any given temperature,” used in semi-auto and recreational rounds because it does not clog the mechanism.
ELEY, “How does temperature affect ELEY ammunition and its lubricant?” — lubricant firms in cold; propellant burns less efficiently as temperature falls; ELEY advises keeping ammunition at a stable temperature.
CCI paraffin melting point commonly reported at ~160 °F. ⚠ Community-sourced, not published by CCI — medium confidence, and flagged as such in the text.
Desiccant comparison — clay releases adsorbed moisture back into the container as temperature rises; silica gel performs steadily and is suited to environments up to ~120 °F; 3A molecular sieve retains moisture far more strongly, releasing only ~40% by 125 °C. Silica gel regenerates at 250–300 °F for 1–2 hours.
Indicating silica gel — blue gel uses cobalt(II) chloride, a Category 2 carcinogen, restricted in the EU and banned in consumer products in several countries; orange gel uses methyl violet and is the safer indicating option.
PETG glass transition ≈ 80 °C / 176 °F; PLA ≈ 55–60 °C / 131–140 °F. The PLA figure is the reason it is ruled out for a load-bearing stack in a vehicle enclosure.
Surplus ammo can empty weights — M2A1 (.50 cal) ≈ 5.2 lb, M19A1 (.30 cal) ≈ 3.7 lb.
Sheffield 12633 .30 cal field box — polymer, stackable, lockable, compression-fit lid rated water and dust resistant; external 11½ × 5 × 7¼ in, internal 9⅜ × 4 × 6 in ≈ 225 in³. ⚠ Empty weight not confirmed from the manufacturer — weigh it.
Synthetic microfibre moisture regain is low but non-zero; the caution in the text is a sizing argument, not a claim that cloth is unsafe. Paperboard is the far larger offender at roughly 6–7% equilibrium moisture content.
Desiccant sizing arithmetic — saturation vapour density ≈ 33.8 g/m³ at 32 °C; silica gel working capacity taken at 150–200 mg per gram at moderate relative humidity. ⚠ Working capacity is a design figure, not a manufacturer specification; the indicating colour is the real feedback loop.
.22 Rimfire, Volume 3, Firearms project — the heeled, outside-lubricated bullet, why the lubricant is a functional component rather than a coating, and ELEY’s moulded packing trays.
.22 Rimfire, Volume 10, Firearms project — rimfire as the dirtiest suppressor host, and the 300–500 round cleaning interval.