The Serial Number field uses an integer type, which forces correct entry. A serial number recorded as "Ruger SP101 0FS3287" is not a serial number — it's a description with a number appended. The integer field enforces the number itself: 0FS3287's numeric component entered cleanly, cross-referenceable against a manufacturer's database or a law enforcement query.
This six-field template is the minimum viable firearm inventory. Not the most detailed possible inventory — that exists in more elaborate templates with acquisition dates, replacement values, and legal documentation fields. This is the record that every owner of more than three firearms should maintain, and most don't.
What Six Fields Accomplish
Manufacturer, Model Number, and Serial Number establish the weapon's identity triangle. Manufacturer plus model identifies the design. Serial number individualizes the specific piece within that production run. Without all three, the record doesn't uniquely identify the firearm.
Type of Gun as a text field captures the classification: semi-automatic pistol, bolt-action rifle, over-under shotgun, lever-action carbine. Free text here is appropriate because the classification vocabulary is too varied to reduce to a useful choice list — the distinction between a DA/SA pistol and a striker-fired pistol matters, as does the difference between a pump-action and a semi-auto shotgun.
Gauge/Caliber as an integer covers the common cases: 12 gauge, 9mm, .308, .22 LR. It acknowledges the limitation acknowledged by its own simplicity — 5.56x45mm NATO becomes 556, .357 Magnum becomes 357. The numeric representation doesn't capture the complete cartridge specification, but it enables filtering by broad caliber category across a collection, which is often the question being asked: how many pieces in 9mm? How much .22 LR do I need to stock?
Picture is the field that makes the serial number record legally useful rather than just numerically correct. A Ruger SP101 serial number means nothing to an insurance adjuster who has never seen a Ruger SP101. The photograph attached to the record shows exactly which piece you're describing — the specific configuration, the condition at documentation, the distinguishing features like an aftermarket grip or a non-standard sight. Together with the serial number, it's a complete identification record.