How many cells should a cartridge safety case have?

Answer: One handover divided by cells per case, plus ten percent.

How far apart are EVA and PE foam?

Answer: Rebound and life. EVA holds set under 6 percent; PE costs a third less and collapses after a year.

Is a relief valve necessary?

Answer: Once the case reaches IP67, yes. Without a vent, vacuum loads the latches.

How many tiers can be stacked?

Answer: From load and deformation. At five tiers the bottom carries 21.5 kg, so 1.8 mm is the pass line.

Does laser marking damage the case?

Answer: No. It affects 0.05 mm of surface and leaves the seal intact, if the code clears the O-ring groove by 5 mm.

How to Choose a Cartridge Safety Case: Five Yardsticks

Quick answer: Five yardsticks settle a cartridge safety case before price does: bore and cell count, foam grade, sealing against relief, stacking versus carry, and marking depth. Put a number against each and the quote matches what the case does.

Sizing a Cartridge Safety Case: Bore, Cavity and Cell Count
Foam Material and Thickness
Sealing Balanced Against Pressure Relief
Stacking Load Versus Carry Method
How Deep Marking and Traceability Should Go
FAQ

1. Sizing a Cartridge Safety Case: Bore, Cavity and Cell Count

The first yardstick fixes the other four. Measure the longest cartridge in the mix, not the most common: a case shared by 9 mm and 5.56 rounds needs cells cut for the rifle round, or the long rounds sit at an angle and the lid will not close flat. Size a cell at length plus 6 mm and diameter plus 4 mm.

Cartridge	Length	Cell
9 x 19 mm	29.7 mm	14 x 34 mm
5.56 x 45 mm	57 mm	14 x 63 mm
7.62 x 39 mm	56 mm	16 x 62 mm
12 gauge	70 mm	20 x 76 mm

Ten columns by ten rows gives 100 cells on a 3 mm wall, and a 420 x 300 x 90 mm interior of a cartridge safety case takes two trays: 200 rounds at 4.3 kg against 3.1 kg for 100. Square cells locate best; a 1 mm corner radius eases the pick.

2. Foam Material and Thickness

Foam is squeezed most often in a cartridge safety case and decides whether cells keep their shape. Thicker is not better: a cell 3 to 5 mm deeper than the cartridge is the sweet spot, since shallower cannot hold the round and deeper defeats gloved fingers.

Material	Hardness and thickness	Best for
EVA	Shore A30, 25 mm	Repeated opening, accurate cells
PE foam	35 kg per m3, 20 mm	One-way transit, volume orders
XPE	45 kg per m3, 18 mm	Frequent handling, exposed corners
PU sponge	25 kg per m3, 30 mm	Large bores, single layer

Write 6 percent as the acceptance limit: no more compression set after 22 hours at 23 degrees Celsius under 50 percent deflection. An insert 1 to 2 mm smaller than the cavity locates by friction without glue, and a 10 mm sheet over a 25 mm routed base stops rounds lifting with the lid.

3. Sealing Balanced Against Pressure Relief

Sealing decides damp storage, relief decides reopening, and the two pull against each other: the tighter the seal, the stronger the vacuum on reopening.

Item	Criterion	Typical failure
O-ring	3.5 mm cord, 25% compression	Groove too deep, corner leak
Waterproofing	IP67, 1 m for 30 minutes	Latch not compressed
Relief valve	Opens at 8 kPa differential	Valve stuck, or no vent
Temperature	minus 30 to 70 degrees Celsius	Gasket hardens in cold

A 3.5 mm cord in a 2.6 mm groove lands at 25 percent compression; a 3 mm groove leaves 14 percent, which holds when static and seeps after a few bumpy trips. Relief needs a 0.5 mm silicone flap over two 2 mm vents opening at 8 kPa, a figure that has to match the route, since plain-to-highland swings pass 20 kPa.

4. Stacking Load Versus Carry Method

Stacking and carrying pull opposite ways. At 4.3 kg loaded, five tiers put 21.5 kg on the bottom lid, so residual deformation after 24 hours of static load has to stay under 1.8 mm, or the second tier latches stop seating. A flat lid with two cross ribs sends that load into the four base corners.

Carry distance sets the hardware. Under 300 m a handle holding 150 N is enough; beyond that, a 38 mm strap, because anything under 30 mm cuts into the shoulder. A 200-cell cartridge safety case belongs on a trolley.

5. How Deep Marking and Traceability Should Go

Marking is where the case meets the management chain: the grades sit within 2 CNY per case while durability differs tenfold. Laser marking should carry 12 characters, four for batch, four for date, two for cavity, two for shift, as a 14 x 14 mm code at the lower left of the lid.

Three positions close the loop: main code outside the lid, matching sub-code on the insert edge, pallet label at the corner, so a split pallet still traces back to its batch. Choose label stock rated minus 40 to 85 degrees Celsius, where the adhesive fails before the print.

Conclusion

The five yardsticks reduce to one habit: turning a choice into a measurement. Cells follow the longest round, foam is accepted on compression set, sealing balances against relief, stacking is released on residual deformation. Written into a specification, they leave little to argue about at sample approval, and that is what makes cartridge safety case selection repeatable.

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.