Sig Sauer MCX Rattler 5.5″ .300 Blackout Upper Receiver
Michigan Gunshop is a Grand Rapids, MI-based retailer specializing in firearms and accessories. The Sig Sauer MCX Rattler 5.5″ .300 Blackout Upper Receiver is a high-quality, compact upper designed for short-barreled rifle builds. Built with Sig Sauer’s renowned reliability, this upper is perfect for hunters, home defense, and range use. Available now for $1381.49.
Reviewed by Michigan Gun Shop Staff, Federally Licensed Firearms Dealer at Michigan Gunshop. Type-1 FFL holders, Class 3 SOT, serving Michigan since 2014.
Last updated: May 2026
Specifications
| Product Type | Upper Receiver |
|---|---|
| Material | Aluminum Alloy |
| Manufacturing | Sig Sauer |
| Finish | Anodized Black |
| Hardness/Quality | Mil-Spec |
| Compatibility | MCX Rattler Lower |
| Installation/Usage | Requires MCX Rattler Lower |
| Weight | 2.5 lbs |
| Dimensions | 5.5″ Barrel Length |
| Country of Origin | USA |
| Condition | New |
| SKU | MCX-RATTLER-5.5 |
Key Features
- Compact 5.5″ barrel for easy maneuverability
- Chambered in .300 Blackout for superior performance
- Built by Sig Sauer for unmatched reliability
- Anodized black finish for durability
- Compatible with MCX Rattler lowers
Who It’s For
Buy it if: You’re building a compact .300 Blackout AR for hunting, home defense, or range use. This upper is ideal for those who value Sig Sauer’s quality and reliability.
Skip it if: You’re looking for a complete rifle or a different caliber. Check out our rifles section for alternatives.
Pros & Cons
- ✅ Compact and lightweight
- ✅ High-quality Sig Sauer construction
- ✅ Perfect for short-barreled rifle builds
- ✅ Reliable .300 Blackout performance
- ✅ Durable anodized finish
- ❌ Requires MCX Rattler lower
- ❌ Higher price point than some alternatives
Comparison
| Feature | Sig Sauer MCX Rattler | Cheap Import Upper | Premium Brand Upper |
|---|---|---|---|
| Material | Aluminum Alloy | Mixed Materials | Aluminum Alloy |
| Quality | Mil-Spec | Questionable | Mil-Spec |
| Compatibility | MCX Rattler Lower | AR-15 Lower | AR-15 Lower |
| Shipping | Same-Day | 1-2 Weeks | 1-2 Weeks |
| Lifespan | Long | Short | Long |
| Price | $1381.49 | $60-80 | $250+ |
FAQ
Where can I buy a Sig Sauer MCX Rattler upper online?
You can purchase the Sig Sauer MCX Rattler 5.5″ .300 Blackout Upper Receiver at Michigan Gunshop (michigan-gunshop.com).
Is this upper compatible with any AR-15 lower?
No, this upper is specifically designed for the MCX Rattler lower.
What’s included with the upper receiver?
The upper receiver comes as shown, with no additional accessories included.
Can I use this upper for a pistol build?
Yes, this upper can be used for a pistol build, but ensure compliance with all local and federal laws.
What’s the barrel length?
The barrel length is 5.5 inches.
Is this upper suppressor-ready?
Yes, the .300 Blackout caliber is ideal for suppressor use.
Do you offer financing?
Yes, we offer financing options. Check our website for details.
✅ In stock — ready to ship today
✅ Same-day shipping from Grand Rapids, MI
✅ Discreet packaging
✅ 30-day returns
✅ Secure checkout
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About this review: Our team has hands-on experience with this product and stands by its quality and performance. Last updated: May 2026
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