How much smaller is the inside of an ammunition box than the outside?

Answer: About ten millimetres per edge, so a four-hundred-and-twenty case measures three hundred and ninety-six inside.

Is a thicker wall always better?

Answer: No. Each millimetre adds roughly one point eight kilograms, while a transverse rib buys stiffness more cheaply.

What sealing class suits open storage?

Answer: IP65 or better with a relief valve. An unvalved body is pumped twice a day once the diurnal swing exceeds fifteen degrees.

How large should the padlock bore be?

Answer: Nine to ten millimetres with a raised boss. Below eight, most shackles will not pass.

How are the five criteria scored?

Answer: Thirty for size and slots, twenty for wall, twenty-five for sealing, fifteen for latches, ten for stacking and marking.

How to Choose an Ammunition Box: Five Criteria and One Scorecard

Quick answer: Measure internal clear dimensions first, then wall thickness and stacking tiers, then sealing class, latch count and padlock bore, and finish with handling and marking. Score the five by weight; anything under seventy points never reaches the price comparison.

Start with internal clear dimensions
Matching wall thickness to empty weight
Sealing class and pressure relief
Latch count and padlock bore
Stacking, handling and marking fields
FAQ

1. Start with internal clear dimensions

The inside of an ammunition box decides whether it works, yet it is the harder side to measure. Draft and corner radii mean a case quoted at four hundred and twenty millimetres externally often measures three hundred and ninety-six inside. Start from the contents envelope plus ten millimetres and derive the outer size.

Nominal	Internal	Slots	Typical fit
420	396	6	short rounds
560	534	8	two layers
780	752	12	long rounds

Denser slots mean thicker dividers, and every millimetre of divider comes out of clear width. Below diameter plus three of slot width, foam stays compressed and the geometry drifts, so use eight-millimetre dividers and lengthen the case rather than squeeze the slots.

2. Matching wall thickness to empty weight

Wall thickness and empty weight move against each other. Rotomoulded polyethylene runs three and a half to five millimetres, and each extra millimetre adds about one point eight kilograms, paid on every return. Stiffness comes from hoop geometry: one transverse rib equals a millimetre of wall.

Ammunition box: closed white case on a steel bench, three front latches, integral handle with a round pressure-relief valve above it, grey shelving behind

A six-kilogram case rated for twenty kilograms carries one hundred and four kilograms on the bottom tier of a five-high stack, which sets the creep check. A thin wall sags at the base centre first, visible only with light raking across the surface.

3. Sealing class and pressure relief

Sealing class follows the store, not the price list. A controlled room takes IP54, a covered shed IP65, an open yard or sea freight IP67 with a relief valve. An unvalved body pumps its gasket twice a day once the diurnal swing passes fifteen degrees.

Class	Build	Suitable store	Check point
IP54	single gasket	indoor	continuous rim
IP65	gasket plus valve	covered shed	membrane intact
IP67	twin gasket, capped	open yard, sea	dry inside

Valves usually crack at zero point two to zero point four bar, quoted with a dust membrane. On the gasket, check solid or hollow section, compression of twenty-five to thirty percent, and joint position; a corner joint is where water first appears.

4. Latch count and padlock bore

Latch count follows length: two at four hundred and twenty millimetres, three at five hundred and sixty, four beyond seven hundred and eighty, always symmetrical. An off-centre middle latch loads the rim unevenly and lifts the long side about two millimetres, where the gasket stops sealing.

Padlock bores are most often missed: below eight millimetres most shackles will not pass, and nine to ten with a raised boss gives compatibility and pull resistance.

5. Stacking, handling and marking fields

Tiers come from the fit between top recesses and base bosses. Recesses under five millimetres deep start walking at the fourth tier; eight millimetres deep with one millimetre of clearance holds a five-high stack within ten millimetres. Multiply tiers by loaded weight and hold the result under the base rating.

Handling rests on a moulded-in handle, forklift apertures and pallet location: a handle rated at twice the loaded weight, and apertures aligned to pallet pitch. Reserve four marking fields, front, sides and lid, the only one visible once stacked.

Criterion	Weight	Pass line	Reject line
Size and slots	30	ten millimetres spare	slot too narrow
Wall and weight	20	three point five plus	base fails load
Sealing and relief	25	matches store, valved	no valve outdoors
Latches and bore	15	three symmetric, nine	bore below eight
Stacking and marking	10	four tiers, four fields	no lid field

Any reject line ends the comparison whatever the total, because each describes a structure that can no longer be changed.

Conclusion

The order cannot be shuffled: internal size, then wall and weight, then sealing and latches, then stacking and marking. The first two decide whether the case works; the last three how long it keeps working. Score all five before discussing price, and an ammunition box stops being a contest between unit prices.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.