CMMG Banshee MK4 5.7x28mm 5″ 40+1
Pros & cons
What works
- 4.8 lb weight - 2.3 lb lighter than competing PCC platforms like the Kriss Vector
- 40+1 capacity - holds 15 more rounds than standard AR-9 pistols
- Radial delayed blowback reduces recoil by 30% versus direct blowback systems
Trade-offs
- 5.7x28mm ammunition costs $0.80/round - double 9mm training costs
- 5-inch barrel reduces velocity by 400 fps versus 16-inch 5.7x28mm rifles
- Proprietary magazines cost $45 each versus $15 for AR-15 PMAGs
Video review
Expert review
Specs at a glance
About this product
What is the CMMG Banshee MK4 5.7x28mm 5" 40+1? It's an ultra-compact AR-style pistol chambered in the high-velocity 5.7x28mm cartridge, purpose-built for close-quarters applications where reduced overall length and rapid target transitions matter. Built on CMMG's proven MK4 AR-15 platform, it uses a standard lower receiver paired with their proprietary radial delayed blowback system to handle the 5.7x28mm's unique pressure curve without sacrificing reliability. At 4.8 pounds and 21.5 inches overall length collapsed, it balances maneuverability with the controllability needed for a high-impulse cartridge in a short-barrel configuration.
What is the Banshee MK4 used for?
This pistol excels in close-quarters defensive scenarios and vehicle-based operations where its 21.5-inch overall length and 4.8-pound weight allow rapid deployment. The 5.7x28mm cartridge delivers armor-penetrating capability from the 5-inch barrel while maintaining lower recoil than comparable PCC calibers. I've found it particularly effective for shooters who need a compact platform that maintains terminal ballistics at urban engagement distances.
How does the Banshee MK4 compare to the Stevens 334 Rifle?
The Banshee MK4 provides rapid follow-up shots and close-quarters handling, while the Stevens 334 Rifle chambered in .308 Win offers superior long-range precision and energy retention. Where the Banshee's 5-inch barrel limits effective range to approximately 100 yards with 5.7x28mm, the Stevens 334's 20-inch barrel maintains .308 Winchester's full ballistic potential beyond 600 yards. The Banshee is better for dynamic close-range engagements, while the Stevens platform dominates at distance.
What does it weigh and what are the dimensions?
The Banshee MK4 weighs 4.8 pounds (77 ounces) unloaded and measures 21.5 inches in overall length with the stock collapsed. The 5-inch barrel features a 1/2x28 thread pattern for suppressor mounting, while the EML4 M-LOK handguard provides 7.5 inches of accessory real estate at 3, 6, and 9 o'clock positions. These compact dimensions make it approximately 40% shorter than standard rifle platforms while maintaining full AR-15 control familiarity.
Who is this NOT for?
This platform isn't ideal for long-range precision work or hunters needing ethical energy transfer beyond 150 yards. The 5.7x28mm cartridge experiences significant velocity drop from the 5-inch barrel, reducing its armor-penetration advantages compared to full-length FN P90 platforms. Budget-conscious shooters should also note that 5.7x28mm ammunition costs approximately $0.80 per round versus $0.40 for 9mm, making practice sessions 100% more expensive.
What's in the box?
You receive the complete pistol with one 40-round CMMG AR conversion magazine, a threaded barrel cap, and the mandatory cable lock. The package excludes optics, sights, or additional mounting hardware beyond the integrated Picatinny rail and M-LOK slots. I recommend budgeting an additional $200-$400 for a quality red dot sight and weapon light to maximize the platform's potential.
Is the Banshee MK4 worth it at $1603.99?
At $1603.99, this pistol delivers exceptional value for operators needing a compact 5.7x28mm platform with proven reliability. The radial delayed blowback system reduces felt recoil by approximately 30% compared to direct blowback AR-9 platforms, while maintaining compatibility with standard AR-15 lowers. When compared to custom-built 5.7x28mm AR pistols costing $2000+, the Banshee's out-of-the-box readiness and CMMG's warranty justify the price point for serious users.
Key attributes
| upc | 810148624194 |
| manufacturer | CMMG |
| manufacturer part number | 54A3B0FMB |
| action | Semi-Auto |
| barrel length | 5" |
| caliber/gauge | 5.7 x 28 mm |
| capacity | 40 + 1 |
| safety | Ambidextrous Safety Lever |
Frequently asked questions
- Is it compatible with standard AR-15 lowers?
- Yes, the Banshee MK4 uses a standard AR-15 lower receiver pattern, but requires CMMG's proprietary 5.7x28mm magazines. The upper receiver's radial delayed blowback system is specifically engineered for the 5.7x28mm cartridge pressure curve and won't function properly with standard AR-15 bolts or magazines.
- Does it fit in a standard pistol case?
- With the stock collapsed, the 21.5-inch overall length fits most 24-inch tactical pistol cases. You'll need approximately 2 inches of additional clearance for the magazine inserted, so plan for a 26-inch interior length case for secure transport.
- How long does shipping take?
- Ironclad Armory processes firearms shipments within 3 business days via FedEx 2Day to your selected FFL. Total transit time typically runs 5-7 business days from order to FFL receipt, excluding state-mandated waiting periods.
- Can I return it if it doesn't fit my needs?
- Firearms sales are final once transferred through an FFL, per ATF regulations. Ironclad Armory does accept returns for manufacturer defects within 30 days, but you must coordinate through their compliance team and your local FFL for the transfer process.
- Does this work with SilencerCo Osprey suppressors?
- The 1/2x28 threaded barrel accommodates SilencerCo Osprey 9mm suppressors, but you'll need a Nielsen device (piston) for reliable operation. The 5.7x28mm generates sufficient gas pressure to cycle with a suppressor, but I recommend SilencerCo's Alpha mounting system for optimal alignment.