Can I size a firearm storage case interior by subtracting wall thickness from the outside?

Answer: No. The outside carries rebates, radii and shrinkage, so the cavity ends up 1 to 2 mm generous.

The drawing says 3.2 mm and I measured 2.9 mm. Is that a reject?

Answer: It depends on the callout. Nominal 3.2 mm with a 2.8 mm minimum passes; plus or minus 0.1 mm fails.

How many tiers should the stack load assume?

Answer: Worst case plus one: three in the warehouse, five on a truck means five.

Where does the price gap between IP67 and IP65 sit?

Answer: In the gasket and the rebate. IP67 needs a 0.4 to 0.6 mm gap and 25 per cent compression.

Does a minus 30 rating force a different resin?

Answer: Only if a cold drop is required. After 4 hours at minus 30, standard copolymer cracks at the corners.

Firearm Storage Case Specifications: Dimensions, Wall and Load

Quick answer: A firearm storage case specification has four blocks — interior clearance, wall and rib pitch, stack load, sealing with temperature — and each needs a target, a tolerance and a method before the drawing reads the same to the toolmaker, the gauge room and the buyer.

What a Firearm Storage Case Specification Must Fix First
Sizing the Interior and the Tolerance Chain
Wall Thickness and Rib Pitch
Stack Load and Case Deflection
Sealing Class and Temperature Range
FAQ

1. What a Firearm Storage Case Specification Must Fix First

The brief is one sentence: one long gun, two magazines, moved by vehicle, stacked three high, overnight at minus thirty. It yields three numbers: clearance, stack height, ambient temperature.

The first page holds numbers only.

Parameter	Callout	Measurement	Drift
Interior length	1180 mm, plus or minus 0.8	Calipers, 3 points per end	Shrinkage low
Sidewall	3.2 mm nominal, 2.8 mm minimum	Ultrasonic, four points	Thin near gate
Rib pitch	120 mm	Tape along the long side	Hidden by foam
Stack load	5 high, 24 hours, set under 2 mm	Lid centre after load	Top units ignored

A longer interior raises sidewall bending with the square of the span, so wall grows and rib pitch shrinks. On any firearm storage case, lock the interior first, then wall and rib pitch, then a stack test.

2. Sizing the Interior and the Tolerance Chain

Size the interior from the contents, not the outside: a rifle 1100 mm long with 30 mm buffer each end gives a 1180 mm cavity at 10 per cent foam compression.

Firearm Storage Case: three tan cases on dry grass, the middle open with grey foam cut into compartments, a rolled bundle on a wooden bench

On that cavity, shrinkage 0.6 per cent, forming tolerance plus or minus 0.5 mm, foam plus or minus 1.5 mm and a 0.3 mm rebate stack to 4.1 mm worst case. At 0.5 per cent instead of 0.65 the cavity is 1.8 mm short, enough to jam a rifle butt.

Add the chain worst case, not by root sum square. Keep the rebate at 0.4 to 0.6 mm or the gasket stops compressing.

3. Wall Thickness and Rib Pitch

Thicker is not safer. A firearm storage case in this class starts at 3.2 mm; at 4.0 mm cooling climbs 55 per cent and sink follows; below 2.6 mm corners crack. Rib pitch follows span: no rib under 120 mm, then one at 2.5 times the wall.

Interior length (mm)	Sidewall (mm)	Rib pitch (mm)	Rib height (mm)	Base
Up to 900	3.0	140	7.5	Grid
901 to 1200	3.2	120	8.0	Grid, gussets
1201 to 1500	3.5	110	9.0	Double grid

Thickness is read by ultrasonic gauge, one point per side, against 88 per cent of nominal. Rib pitch is checked in the mould.

4. Stack Load and Case Deflection

Stack load needs three numbers: payload, tiers, permitted set. Thirty-eight kilograms, five tiers, twenty-four hours, set under 2 mm survives a warehouse; stackable alone shifts the risk.

Firearm Storage Case: close view of a tan case side, two latches and a hinge scuffed, lid gasket visible in the joint, cracked ground behind

The bottom lid carries 152 kg over 1180 by 420 mm, about 3 kPa. Modest, yet a flat panel sags past 3 mm a day; one cross rib brings it under 1.5 mm. Read lid centre, sidewall and base corners.

5. Sealing Class and Temperature Range

Two digits are not a specification. IP67 is 1 m of water for 30 minutes; IP65 is 12.5 litres per minute of jet for 3 minutes. Gasket set sits at 25 to 30 per cent: below 20 it leaks, above 35 closing force passes 180 N.

Every firearm storage case drawing should split the range. Storage runs minus 30 to plus 60 Celsius for 48 hours; transport adds 70 Celsius for 4 hours and a 1.2 m drop at minus 30.

Item	Callout	Condition	Verdict
Ingress	IP67	1 m, 30 minutes	No water inside
Heat ageing	60 Celsius, 48 hours	Read after 2 hours	Within 0.3 per cent
Cold drop	Minus 30, 4 hours, then 1.2 m	Six faces	No crack, latches shut

Conclusion

A specification translates field facts into toleranced numbers, and a repeatable method keeps them honest. Derive the interior from the contents, tie wall and rib pitch to span, state payload and set, pair every sealing figure with its test condition. Then the firearm storage case specification holds one set of numbers for toolmaker and dock.

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.