Why does a firearm protective case use a one-way tolerance?

Answer: Foam compresses, walls do not. Growing the cavity gives assembly room; shrinking it forces a tool change.

Is 4.5 mm enough, or should the wall go to 6 mm?

Answer: It depends on the load. Six millimetres adds a third more weight and sink marks.

How many stack levels belong on the drawing?

Answer: Real storage height plus one. Four high means checking five, because mixed stacks load the bottom unit harder.

Is IP67 worth the price over IP65?

Answer: Only if it truly gets submerged. For rain and hose-down, IP65 is enough.

If the range says minus 30 Celsius, is a cold drop still needed?

Answer: Yes. Cold storage measures distortion, the drop measures brittle fracture, and the height drops with temperature.

Firearm Protective Case Specifications: Size, Wall and Load

Quick answer: A firearm protective case specification is built backwards from the load list into four measurable numbers: internal size with one-way tolerance, wall thickness with rib spacing, static stack load, and sealing range.

Deriving a Firearm Protective Case Spec from the Load List
Internal Dimensions and Tolerances
Wall Thickness and Rib Spacing
Static Stack Load and Drop Height
Sealing Class and Temperature Range
FAQ

1. Deriving a Firearm Protective Case Spec from the Load List

Specifications start with an inventory: longest item 1080 mm, two units side by side 280 mm, a sighted unit 140 mm tall. Add 20 mm of handling clearance and the cavity lands at 1120 by 320 by 160 mm.

Requirement	Drawing parameter	Marked as	Value
Item 1080 mm	Internal length	Basic size, plus only	1120 mm, +2 mm
Two side by side	Internal width	Includes foam	320 mm
Sighted unit	Internal height	Base to lid foam	160 mm
Four-high storage	Top face load	24 hour static	180 kg

Write "approximately" and nothing is written: one supplier works to the upper limit, another to the lower, and the same insert fits one case and jams in the next.

2. Internal Dimensions and Tolerances

Measure the cavity from the inner surface, excluding radii and foam, and give a one-way tolerance: larger, never smaller. Foam takes up slack; a wall cannot give material back.

Shrinkage of 0.5 to 0.7 percent means a one metre case cools 5 to 7 mm short of the tool, so the cavity is cut oversize. The lid step keeps 1.5 to 2.0 mm of clearance to stop rattle without starving the gasket.

Internal length	Size tolerance	Lid step gap	Diagonal difference
Under 300 mm	plus or minus 0.8 mm	1.0 to 1.5 mm	1.5 mm
300 to 800 mm	plus or minus 1.2 mm	1.5 to 2.0 mm	2.0 mm
800 to 1200 mm	+2, minus 1 mm	2.0 to 2.5 mm	2.5 mm

3. Wall Thickness and Rib Spacing

Thicker is not stronger. Past 6 mm, weight, cycle time and sink marks climb together, so a firearm protective case settles at 4.5 mm sides, 4.0 mm lid and 5.0 mm base, buying stiffness with ribs at 90 mm pitch, 12 mm tall on a 6 mm root.

Below 70 mm pitch, weld lines crowd where a dropped case splits.

Zone	Wall	Ribs	Target
Side wall	4.5 mm	90 mm pitch, 12 mm tall	Lateral crush
Lid	4.0 mm	Square grid, 110 mm pitch	Resistance to sag
Base	5.0 mm	6 mm root	Wear and load

Runs on an 1800 tonne press; thickness is judged at plus or minus 0.2 mm on the lowest of four readings.

4. Static Stack Load and Drop Height

Load has two lives: time under pressure in a warehouse, distance fallen in a truck. An empty firearm protective case weighs 9.5 kg and carries 27 kg loaded, sitting four high, so the bottom unit takes about 81 kg; design to 180 kg on the top face for 24 hours with 1.2 mm of residual set.

Impact is separate. Drop at 1.5 m onto concrete across six faces, three edges and one corner, ten drops, then accept no through crack, no released latch and no lid shift beyond 1.5 mm. Below freezing the height falls to 1.2 m as the resin loses toughness at minus 25 Celsius.

5. Sealing Class and Temperature Range

Never write "waterproof" alone. IP67 means 30 minutes at one metre with no water inside; for rain and washdown, IP65 costs less and a firearm protective case rarely needs more.

Gasket compression belongs between 25 and 30 percent, so groove depth and cord diameter are paired: under 25 percent it leaks, over 35 percent it takes a permanent set. State minus 30 to 60 Celsius with a dwell time at each end.

Test	Condition	Pass line
Ingress	IP67, 1 m, 30 min	No visible water
Cold	minus 30 Celsius, 4 h	No cracking, latches work
Heat	60 Celsius, 24 h	Under 0.3 percent growth
Thermal shock	minus 25 and 55 Celsius, 3 cycles	Gasket free of set

Operating tests add latch cycles: retention at 60 Celsius stays within 10 percent of 220 newtons.

Conclusion

A specification earns its name when four claims become four readings: it fits, does not crush, does not split, does not leak. Give the cavity a one-way tolerance, pair each wall with its rib pitch, keep static load and drop height apart, and attach dwell times to every temperature claim. Then a firearm protective case drawing controls the product rather than describing it.

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.