Headspace comes up constantly in precision rifle circles — and gets glossed over just as often. If you're installing a pre-fit barrel, building a custom rifle, or just buying a used gun, understanding headspace isn't optional. Here's everything you need to know.
What Is Headspace?
Headspace is the distance from the bolt face to the point in the chamber where the cartridge case stops. Where exactly a case 'stops' depends on the cartridge design:
• Rimless bottleneck cartridges (like 6.5 Creedmoor, .308, 6mm) headspace off the shoulder
• Rimmed cartridges headspace off the rim
• Belted magnums headspace off the belt
Why Headspace Matters
Safety first: If headspace is too excessive, cases will stretch when fired. Repeated stretching leads to case head separation — where the brass literally splits near the base. This is a catastrophic failure mode that can injure a shooter. Insufficient headspace (too tight) means cartridges may not chamber or chamber with excessive resistance.
Accuracy second: Even within the safe range, headspace variation affects how consistently the case positions in the chamber before firing. Consistent headspace contributes to consistent ignition and consistent bullet release — which matters when you're chasing tight groups.
Go, No-Go, and Field Gauges
Headspace gauges come in three sizes for any given cartridge:
• Go gauge: A chamber with correct minimum headspace should close fully on a go gauge. If the bolt doesn't close on a go gauge, headspace is too tight.
• No-go gauge: The bolt should NOT close on a no-go gauge in a properly head spaced chamber. If it does, the chamber is too long.
• Field gauge: The absolute maximum safe headspace. If the bolt closes on a field gauge, the rifle is considered unsafe to fire with factory ammo.
We recommend Manson or JGS headspace gauges — both are trusted by gunsmiths and precision shooters across North America.
Headspace and Pre'-fit Barrels
When you install a shouldered pre-fit on an IBI HMB or Deadline action, we can guarantee correct headspace because we're machining the barrel specifically for that action family. The shoulder contacts the action face and headspace is set mechanically — no guesswork. For barrel nut style pre-fits, or when fitting a shouldered pre-fit to a non-IBI action, you must verify headspace with gauges before firing. Always. No exceptions. If you're uncertain or don't have the gauges, bring the rifle to a qualified gunsmith. It takes five minutes and it's not worth skipping.