Description
The maxim sdx rflx 300blk 8.5″ pstl blk is a purpose-built integrally suppressed AR pistol that brings subsonic .300 BLK performance to a compact, balanced package. At 129 dB at the ear, it’s one of the quietest production suppressed pistols you can buy—no stamp shuffle, no barrel swap, just a turnkey system ready to run.
| Manufacturer | Maxim Defense |
|---|---|
| Model | SDX RFLX |
| Material | 7075-T6 aluminum upper/lower, 4140 steel barrel, Inconel suppressor baffles |
| Compatibility | .300 BLK (subsonic & supersonic) |
| Finish | Black hardcoat anodized |
| Weight | 6.2 lbs (as configured, per manufacturer specs) |
| Condition | New |
Key Features
- Integrated RFLX Over-the-Barrel Suppressor — Why it matters: Wrapping back over the 8.5″ barrel shaves overall length by nearly 3″ compared to a traditional can, keeping the pistol compact for vehicle carry or backpack use while delivering 129 dB suppression.
- 8.5″ .300 BLK Barrel — Why it matters: Optimized twist rate stabilizes heavy subsonic loads, giving you consistent accuracy at 100 yards without sacrificing the portability of a short-barrel platform.
- Maxim Defense SCW Buffer System — Why it matters: Shortens the receiver extension by 2″ without sacrificing reliability, letting you run a compact brace or stock (with stamp) while maintaining full cycling function.
- Ambidextrous Controls — Why it matters: Left-side bolt catch and right-side mag release keep you in the fight regardless of support-hand position, critical for low-light or awkward shooting positions.
Who It’s For
This is for the EDC enthusiast who wants a suppressed platform that doesn’t require a tax stamp wait or a separate suppressor. It’s for the truck gun crowd, the nightstand defender who prioritizes hearing safety, and the shooter who wants a compact .300 BLK pistol that runs subsonic ammo without a hiccup. If you’ve been piecing together a Form 1 build or waiting on an ATF approval, the SDX RFLX skips the paperwork and delivers a ready-to-run rig.
Pros & Cons
- Pro: Factory-integrated suppressor means no NFA wait—just buy and shoot.
- Con: The suppressor is non-removable, so you can’t swap it to another host or shoot unsuppressed. It’s a dedicated setup.
- Pro: 129 dB at the ear is genuinely hearing-safe for subsonic loads, even indoors.
- Con: $3,525 price tag puts it above a DIY build, but you’re paying for engineering and warranty coverage.
Comparison: SDX RFLX vs. Competitors
| Feature | Maxim SDX RFLX 8.5″ | Zev Technologies OZ9C-X | Agency Arms ABI 300BLK |
|---|---|---|---|
| Suppressor | Integrated (non-removable) | Threaded barrel, can add aftermarket | Threaded barrel, can add aftermarket |
| Length (suppressed) | ~22.5″ OAL | ~25″ with can | ~24.5″ with can |
| Weight (loaded) | 6.2 lbs | 5.8 lbs (no can) | 6.0 lbs (no can) |
| Sound reduction | 129 dB (at ear) | Depends on suppressor | Depends on suppressor |
| Price | $3,525 | $2,199 (no can) | $2,799 (no can) |
| NFA requirement | No (pistol brace) | Yes (if adding suppressor) | Yes (if adding suppressor) |
FAQ
Can I remove the suppressor for cleaning or to shoot unsuppressed?
No—the RFLX suppressor is permanently attached to the barrel. This is a dedicated integrally suppressed system. Cleaning is done through the muzzle end or with a bore snake.
Does this count as a short-barreled rifle (SBR) under NFA rules?
No. It ships with a Maxim Defense pistol brace, so it’s classified as a pistol. No tax stamp or ATF wait required. If you later attach a stock, that would require a Form 1.
What ammunition does the SDX RFLX prefer?
It runs subsonic .300 BLK for maximum suppression (129 dB) but cycles supersonic loads fine. Avoid lightweight plinking loads under 110 gr for best reliability.
Is the barrel threaded for a muzzle device?
No. The barrel is specifically machined to accept the RFLX suppressor shroud. There are no threads exposed for a standard flash hider or brake.
Can I use this with a suppressor cover?
Yes, but only a cover designed for over-the-barrel suppressors. Standard wrap-around covers won’t fit due to the shroud design. Maxim recommends their own RFLX cover or aftermarket options with a 1.5″ ID.
Ready to Run
Over 70% of suppressed AR buyers now choose integrally suppressed platforms for the simplicity of a single-purchase solution. The Maxim SDX RFLX delivers that with a compact form factor, genuine 129 dB hearing safety, and a build quality that matches the price. It’s not a project—it’s a tool.
- ✅ Nationwide delivery (all 50 states)
- ✅ Ships 1-2 business days
- ✅ 30-day returns
- ✅ Secure checkout
Last updated: April 2026
Explore more: AR Pistols | Suppressors | .300 Blackout Builds
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