Squib Load Detection: Catch Light Charges Before They Ship
A squib is one of the quietest failures in ammunition and one of the most expensive. The round goes off with a pop instead of a bang, the shooter may not notice, and the next trigger pull sends a full-power round into a barrel that's already blocked. For a manufacturer, the defect that started it was a light charge that looked like every other round in the box.
This post covers what a squib load is, why a bore obstruction turns it into a destroyed firearm, what manufacturer recall notices say about the cause, and where squib load detection fits on a production line.
What a squib load is
SAAMI, the industry's standards body, defines a squib load as "A cartridge or shell which produces projectile velocity and sound substantially lower than normal. May result in projectile and/or wads remaining in the bore."
The second sentence is the dangerous one. SAAMI defines a barrel obstruction this way: "Also called bore obstruction. A foreign object or material in the bore of a barrel which prevents unhindered passage of projectile(s) when fired." A bullet stuck partway down the barrel from a squib is exactly that kind of obstruction.
The NRA Family article How to Handle Squib Loads and Hangfires explains why it matters for factory product and not just handloads: "While squibs are usually attributed to faulty powder charges, which in turn are attributed to careless reloaders, they can happen with any ammunition." The author adds: "I've seen high-quality factory ammo yield a squib or two."
Why the second shot does the damage
The squib round itself is rarely the event that injures someone. It's the round fired behind it. A shooter who hears a soft report, feels light recoil and keeps firing, or who runs a trained malfunction drill without checking the bore, drives a second bullet into the first one.
User reports on shooting forums show how that plays out. These are first-hand accounts, not verified findings, and they don't establish which ammunition or lot was involved:
- On The High Road, member Will5A1 described (user-reported) a soldier on a qualification range who "had a squib load, he didn't realize it, performed, as he was trained to do an immediate action drill and attempted to fire another round with bullet from the squib obstructing the bore. The barrel bulged but did not come apart".
- In the same thread, the same member described a student in a basic pistol course who, firing factory ammunition, "managed to stack 4 bullets in the barrel" of a revolver, leaving "The frame is bent with barrel split forward of the forcing cone."
Both outcomes come from one root cause upstream: a round left the factory with too little energy to clear the barrel.
What recall notices say about light charges
Ammunition isn't regulated by a federal recall agency in the way most consumer products are, so recalls are voluntary manufacturer notices. That makes those notices the best public record of how squibs escape production. Several name the charge directly.
SIG SAUER, 2022. The SIG SAUER recall notice for 9mm 115 gr Elite Ball FMJ says portions of Lot No. JDAR0815 "may have powder charge variations that could result in a bullet remaining in the barrel (i.e., a bullet-in-bore obstruction). Firing a subsequent bullet into a bore obstruction could cause firearm damage, rendering the firearm inoperable and subjecting the shooter and bystanders to a risk of serious personal injury." We covered this notice alongside others in Ammunition Recall Notices: What Out-of-Spec Rounds Reveal.
Winchester, 1995. As reprinted in the AFTE Recall/Safety Warning List, Winchester determined that "a small number of cartridges of LOT NUMBER 137HF22 Super-X7 30-06 Springfield, 180 gr. Power-Point Ammunition may contain low powder charges. These low powder charges can cause a squib, or weak shot, which could result in a bullet remaining in the barrel after firing, obstructing the barrel."
Magtech, 1992. The same AFTE list reprints a notice stating that Magtech "has recently received several reports of a "squib", or low-powder load, in Magtech brand .45 ACP ammo. Each of these reports has been traced to ammunition manufactured in LOT NUMBER L-602."
Three different makers, three decades apart, and the same pattern: a small number of light rounds inside an otherwise normal lot, found after the product reached customers.
Not every squib is a weight problem
Honest inspection planning starts with what a method can't see. Not every squib recall points to the amount of powder.
Winchester's 2021 9mm Luger 115 gr recall says the affected ammunition "may contain propellant that does not properly ignite and burn when the cartridge is fired." In that case the problem is how the propellant burns. A round with the right weight of propellant that doesn't burn properly can weigh the same as a good round, so weight inspection shouldn't be expected to catch it. That's a propellant and process-control question, and it belongs in incoming material testing and ballistic lot acceptance.
Where the notice points to "low powder charges" or "powder charge variations", weight is the direct measurement.
Squib load detection by weight
A light charge changes the total weight of a loaded round. That's the principle behind 100% weight inspection, and it's why the AccuWeigh 360 lists "a light or heavy powder charge" among what weight catches, along with a missing primer, a wrong or defective projectile and damaged brass.
What matters for squib load detection, per the AccuWeigh 360 product page:
- Resolution. Repeatability is "0.1 grain at one standard deviation on the 10 gram cell; 0.2 grain on the 30 gram cell; 0.6 grain on the 80 gram (1,234 grain) cell." Limits can be set "as tight as 0.1 grain or as wide as ten grains for large rounds."
- Every round, not a sample. The AccuWeigh 360 is modular. It starts at 3,600 parts per hour with a single weigh cell, or 28,800 in an eight-hour shift, and scales past 12,000 parts per hour as weigh cells are added.
- Inline with the loader. Fed from a loader's output, "it pulls out-of-spec rounds as they are made, so a bad setup is caught in the first rounds rather than the whole lot."
- Fail-safe rejection. Ammo Inspector's firewall decision logic "means a defective cartridge or component can never be passed as good. The logic fails safe: when a reading cannot be trusted, the part is rejected rather than assumed good."
- A record for the lot. The system stores "a record of every part weighed", with Six Sigma compatible output and an optional remote data feed.
One practical point for QC managers: total-round weight includes the case, primer and projectile as well as the charge. The tighter the weight spread of those components, the smaller the charge error that stands out from normal variation. That's one reason manufacturers sort brass and projectiles by weight class before loading, and set limits per cartridge rather than using one generic window.
Why sampling lets squibs through
The recall notices above share a detail: "portions" of a lot, "a small number of cartridges", "several reports". Squib-causing defects tend to be rare and intermittent, such as a powder measure hanging up, a bridged charge or a station hiccup, not a steady drift that every sampled round would show.
A sampling plan is built to estimate the average quality of a lot. It isn't built to find a handful of bad rounds among hundreds of thousands. We worked through the math on a real double-charge lot in Why Sampling Misses the Bad Round: 100% Weight Inspection. The same logic applies to light charges: if the defect is rare, the sample probably won't contain it.
The cost side for manufacturers
A squib that escapes a plant can cost far more than the round itself:
- Recall scope. Without round-level records, a manufacturer may have to pull a whole lot, or several lots, to cover a few bad rounds.
- Customer harm and liability. As the SIG SAUER notice puts it, the result can be "firearm damage, rendering the firearm inoperable and subjecting the shooter and bystanders to a risk of serious personal injury."
- Brand trust. Recall notices stay public for years, and the AFTE list still carries notices from the early 1990s.
Inspection data cuts both ways. A documented record that every round in a lot was weighed and passed is useful evidence when a field complaint comes in, and a record of where the rejects clustered helps narrow a recall to the affected production window.
Where weight inspection fits in the line
For most loaders, squib load detection by weight works best in two places:
- Inline at the loader output, so a charging fault is caught in the first rounds rather than after a full lot is loaded.
- As a final check before boxing, so nothing out of limits reaches packaging.
Feeding matters too. The AccuWeigh 360 runs from an AccuFeed collator or a Dillon-style case feeder, and pairs with AccuVision vision inspection when dimensional and surface defects need to be caught as well. Vision and weight see different defects, so many lines benefit from both.
Talk to us about your line
If light charges or squib reports have shown up in your complaints file, or you're relying on sampling to catch a defect that only shows up a few times per lot, tell us your calibers, components and volume per shift. We'll spec the weigh-cell count your line needs. Contact Ammo Inspector to start the conversation.