If you've played airsoft long enough with a Thunder B, you know the frustration. You cook it, you throw it — and nothing happens. The shell didn't pop. Your opponent walks right through. The round is over before it started.
The Thunder B is one of the most popular sound grenades in airsoft, but its CO2-dependent design comes with a list of reliability problems that have plagued players for years. Plastic shells that randomly detonate in your pouch. CO2 cartridges that misfire in cold weather. Shrapnel flying where you don't want it. And a cost per throw that adds up fast.
There's a better way.
What Is a Thunder B Conversion Kit?
A Thunder B conversion kit replaces the original CO2 shell system with a blank cartridge-based mechanism. Instead of relying on a 12g CO2 canister and a brittle plastic shell, you load a standard 9mm PAK blank cartridge into the adapter. The grenade detonates on impact — instantly, every time.
The Brey Tac Blank Kit is the first kit of its kind to make this conversion possible. It turns your existing Thunder B into a blank-fired impact grenade with zero delay and zero CO2 dependency.
Why the Standard Thunder B System Falls Short
The CO2 shell design works — sometimes. But consistent? Rarely. Here's what players deal with regularly:
Cold weather misfires. CO2 pressure drops significantly when temperatures drop below 60°F. In winter milsim events or indoor fields with aggressive HVAC, your Thunder B becomes unreliable right when you need it most.
Random pre-detonation. The plastic shell is under pressure the moment it's loaded. A hard bump in your pouch, a bad land after a crawl, and it can go off before you throw it. This isn't just wasteful — it's a safety and stealth issue.
Plastic shrapnel. When the shell bursts, it sends fragments in every direction. Most experienced players have a story about catching a piece of shell at close range.
Cost per throw. A single CO2 cartridge plus a replacement shell runs anywhere from $1.50 to $3.00 per throw depending on your source. That adds up to real money across a season.
How the Blank Kit Solves All of This
The Blank Kit addresses each of these issues at the hardware level.
Impact detonation. There's no delay, no pressure release timing. The grenade detonates the moment it strikes a surface. In CQB, that extra 0.3 seconds of predictability is the difference between a clean entry and a failed breach.
No CO2 dependency. Blank cartridges are not affected by temperature. They fire at 20°F the same way they fire at 90°F. Your grenade performance is consistent regardless of conditions.
No plastic shrapnel. The conversion kit uses an aluminum shell. There are no fragmenting plastic components. Clean use, every time.
Cost per throw drops to cents. A 9mm PAK blank cartridge costs roughly $0.25–0.40 depending on where you buy. Over a season of regular play, the Blank Kit pays for itself many times over.
What's in the Kit
The Brey Tac Blank Kit V2 includes everything you need to convert your Thunder B:
- Pin Assembly (Blank Kit)
- 9mm PAK Cartridge Adapter
- Custom shell with magnetic trigger
- Compatible with all standard Thunder B tubes
The V2 improves on the original with a redesigned ignition system that's easier to swap out, better compatibility with the Thunder B cylinder, and 360-degree sound diffusion through radial holes — making it louder and more directional than a standard CO2 pop.
It also works as a bundle with the Thunder B Main Core if you're starting from scratch.
Is It Legal in the USA?
Yes. 9mm PAK blank cartridges are legal in all US states without a firearm license. They are not live ammunition — they produce sound only, with no projectile. Standard airsoft field rules apply, but the cartridges themselves require no special permits to purchase or transport.
If you're unsure about your specific state or local field rules, check with your field owner before your first use. Most fields that allow sound grenades have no issue with blank-fired systems.
Setting It Up
Setup takes under five minutes the first time. The Blank Kit threads into the Thunder B Head and replaces the standard firing pin. Load a blank cartridge into the adapter, assemble the shell, and it's ready.
A detailed setup video guide here. If you run into any questions, Brey Tac support is reachable at shoot@breytac.com.
The Tactical Difference
Players who switch to the Blank Kit consistently report the same thing: they actually start using their grenade.
With the CO2 system, grenades become expensive insurance. With the Blank Kit, a throw costs less than a cup of coffee and fires every single time. That changes how you approach every CQB entry. Instead of saving the grenade for the "right" moment, you use it as a standard part of your breach sequence — because you can afford to.
That's the tactical shift. Not just a better product. A different way to play.
Ready to upgrade your Thunder B?
Shop the Blank Kit V2 →
Already have the kit? Add the Blank Kit Holder for MOLLE-compatible carry and the Cartridge Holder for fast reloads on the field.