Otter Creek Labs Polonium K

Otter Creek Labs Polonium K

The Otter Creek Labs Polonium K is a compact, hard-use 5.56 suppressor built from H900 heat-treated 17-4 stainless steel in a CNC welded tubeless design. It is 4.8 inches long, weighs 11.5 oz without a mount, and measures 1.625 inches in outer diameter. The 6mm bore is compatible with 5.56 NATO, .223 Remington, and all 6mm/.243 cartridges including 6 ARC, 6mm Creedmoor, 6mm Dasher, and .243 Winchester. The Polonium K uses industry-standard 1.375x24 HUB rear threads and has a 7.5-inch minimum barrel length requirement for 5.56/.223. Full-auto rated and belt-fed certified with no marketing fluff attached.

If you are working through the NFA process for the first time, our complete guide to buying a suppressor online has everything you need.

What Makes the Polonium K Different

Otter Creek Labs does not do inflated dB numbers or fancy marketing language. They build suppressors for the working shooter and let the performance make the case. The Polonium K earns its reputation the same way every OCL product does: by being built right, priced honestly, and performing in conditions where lesser suppressors quit.

The H900 heat treatment is not a minor detail. H900 is the highest-strength precipitation hardening condition for 17-4 stainless steel, providing exceptional yield strength and erosion resistance under sustained full-auto fire. Most suppressors use standard 17-4 without this specification. The Polonium K does not cut that corner.

The tubeless design means the baffle structure and outer shell are CNC welded as a unified assembly rather than a separate core inside a tube. The result is higher internal volume for sound reduction, less weight, and no tube-to-core weld joint to fail under hard use. The external geometry is not cosmetic. The material removed from the exterior creates 10% more surface area compared to a conventional design, which means the Polonium K sheds heat and cools faster after sustained strings of fire.

The integrated internal and external flash hider is built into the suppressor, not a swappable accessory. On a 5.56K-length suppressor this matters especially in low-light and night vision environments where flash signature reduction is critical. OCL's integrated design outperforms most separate flash hider attachments on competitors.

Polonium K vs Polonium: Which One Is Right for You

The Polonium K and the full-length Polonium share the same H900 17-4 stainless construction, same HUB threads, same flash hider design, and same performance philosophy. The difference is size and weight. The Polonium is 5.8 inches and 13.5 oz. The Polonium K is 4.8 inches and 11.5 oz. One inch shorter. Two ounces lighter.

If you run a short-barreled rifle, an MK18-pattern build, or any setup where total package length is a practical consideration, the Polonium K is the right call. If length is not a constraint and you want every bit of available sound suppression, the full Polonium has more internal volume to work with.

Otter Creek Labs Polonium K Specifications

Otter Creek Labs lets the specs speak for themselves. Here's exactly what you're getting.

• Caliber: 5.56 NATO, .223 Remington, 6mm/.243 (6 ARC, 6mm Creedmoor, 6mm Dasher, .243 Winchester)
• Length: 4.8 inches
• Weight: 11.5 oz (without mount)
• Outer diameter: 1.625 inches
• Bore diameter: 6mm
• Material: H900 heat-treated 17-4 stainless steel
• Construction: CNC welded tubeless design
• Rear thread: 1.375x24 (HUB standard)
• Minimum barrel length: 7.5" for 5.56/.223 and 7.62x39
• Full-auto rated: Yes
• Belt-fed rated: Yes, on 16" 5.56 belt-fed machine guns. Do not exceed 300-round string without cool down.
• Flash hider: Integrated internal and external
• Warranty: Lifetime, no BS

Important: The Polonium K is a 5.56 suppressor with a 6mm bore. You cannot fire 6.5mm or 7.62mm projectiles through it. The barrel length restrictions listed above apply to calibers the bore will accept. The 16" minimum for .300 Win Mag applies to the Polonium-30, not this suppressor.

Mounting System Compatibility

The Polonium K uses 1.375x24 HUB rear threads, the industry-standard thread pitch that gives you full flexibility in mounting solution. Compatible systems include Dead Air KeyMo and Xeno, SilencerCo ASR, Q Plan-B, Griffin Armament mounts, YHM Kurz and Phantom, and any other mount built to the 1.375x24 HUB standard. The included 1/2x28 direct thread adapter covers most 5.56 hosts straight out of the box.

What's in the Box

Every Otter Creek Labs Polonium K ships with:

• Polonium K suppressor
• 1/2x28 direct thread adapter
• Tube clamp for installing and changing mounts
• Instruction pamphlet
• Stickers

Note: OCL states direct thread adapters may vary in appearance from product photos.

Who the Polonium K Is Best For

The Polonium K is for shooters who run their suppressor hard and do not want to baby it. It lives on MK18 and short-barrel 5.56 setups that see sustained fire, night operations where flash signature matters, and any rifle build where keeping the overall package short is not negotiable.

It is not for the shooter who wants the absolute quietest can regardless of size. The full-length Polonium will outperform it slightly at the muzzle due to added internal volume. But for the price, the weight, the size, and the level of hard use it tolerates, the Polonium K has earned one of the strongest reputations in the 5.56K suppressor category.

For shooters evaluating multiple caliber coverage, the Polonium-30 handles everything from full-auto 5.56 up to .300 RUM, though OCL is refreshingly honest that a 30-caliber bore gives up some 5.56 performance compared to the Polonium K. If you are primarily a 5.56 shooter, the K is the right answer.

Frequently Asked Questions: Otter Creek Labs Polonium K

What calibers can the Polonium K suppress?

The Polonium K has a 6mm bore and is rated for 5.56 NATO, .223 Remington, and all 6mm/.243 cartridges including 6 ARC, 6mm Creedmoor, 6mm Dasher, and .243 Winchester. It cannot be used with 6.5mm or 7.62mm projectiles.

Is the Otter Creek Labs Polonium K belt-fed rated?

Yes. The Polonium K is full-auto rated and responsible belt-fed rated on 16" 5.56 belt-fed machine guns. OCL specifies not exceeding 300-round strings without a cool down period.

What is the minimum barrel length for the Polonium K?

The Polonium K requires a minimum barrel length of 7.5 inches for 5.56/.223 and 7.62x39. For 6 ARC and 6.5 Grendel, the minimum is 10.5 inches.

What is the difference between the Polonium K and the full-length Polonium?

The Polonium K is 4.8 inches long and weighs 11.5 oz. The full-length Polonium is 5.8 inches and weighs 13.5 oz. Both use the same H900 17-4 stainless construction and 1.375x24 HUB threads. The K trades a small amount of sound suppression for one inch in length and two ounces in weight.

What mounting systems are compatible with the Polonium K?

The Polonium K uses 1.375x24 HUB rear threads, compatible with Dead Air KeyMo and Xeno, SilencerCo ASR, Q Plan-B, Griffin Armament mounts, YHM Kurz and Phantom, and any other HUB-standard 1.375x24 mounting system.

What is the Polonium K made of?

The Polonium K is constructed from H900 heat-treated 17-4 stainless steel in a CNC welded tubeless design. H900 is the highest-strength precipitation hardening condition for 17-4 stainless steel.