MM Compensator Fit Guide: Harrier, Seagull and Firefly Compared
Choose the compensator for the exact blaster, installed barrel and front furniture, then confirm the spin device fits inside it. For a Harrier with a 310 mm barrel, the named Short model is the documented starting point. For a Seagull's shortest boxed barrel, choose its Seagull Short model. For a Firefly Stinger, match the cap to the Stinger furniture variant.
A compensator can finish the front profile and enclose a compatible BCAR. It does not convert one platform's mounting interface into another, and enclosure does not mean that every attachment sits flush with every barrel. The most useful fit check is the complete assembled combination.
Documented dimensions and configurations
| MM product | Documented configuration | Body length including tip | Tip hole |
|---|---|---|---|
| Harrier Compensator Short | 310 mm barrel | 90 mm top / 95 mm bottom | 34 mm |
| Harrier Compensator | Listing specifies 368 mm barrel | 126 mm top / 131 mm bottom | 34 mm |
| Seagull Compensator Short | Shortest boxed barrel | 98 mm | 29 mm |
| Seagull Compensator | MM BCAR protrudes with longest boxed barrel | 113 mm | 29 mm |
| Firefly Stinger Compensator Mag Cap | Corresponding Stinger front furniture | No verified dimension used here | Confirm exact device clearance |
Harrier: identify the actual barrel length
The Short and regular Harrier compensators have separate product descriptions and different lengths. Use the numeric barrel reference in the selected listing. In particular, the regular compensator page calls its reference barrel 368 mm and describes it as a boxed barrel; package descriptions elsewhere may use different nominal lengths. “Stock barrel” is therefore an insufficient order instruction.
If your barrel is sold as 370 mm or is a replacement, send the shop its exact product and configuration rather than assuming a match from the nearest number. Confirm the installed attachment position at the same time. A longer barrel can move the BCAR forward even when the surrounding compensator still attaches to the blaster.
Seagull: Short and regular do not promise the same enclosure
The Seagull Short listing describes a flush arrangement around the shortest boxed barrel. The regular Seagull compensator explicitly warns that an MM BCAR protrudes when the longest boxed barrel is used. That warning is a purchasing detail, not a defect to solve by forcing the device farther back.
If your goal is a fully enclosed appearance, state it when ordering and confirm the whole configuration. If you are content with a protruding attachment, check that it still mounts securely and has the required exposed barrel engagement. The 29 mm tip opening is useful reference information, but it is not a complete internal-cavity drawing.
Firefly: match the Stinger body and BCAR variant
The Firefly Stinger cap belongs to its corresponding Stinger furniture. A separate Slim Profile cap is also catalogued; the similar name does not establish that the two caps interchange. Identify which kit is installed before buying the finishing piece.
Firefly also has a dedicated short-bodied BCAR200 because its exposed barrel is shorter. The standard BCAR200 and Firefly version should not be treated as the same mounting package. Check the spin device independently from the outer cap so a correct-looking enclosure does not hide an unsuitable barrel connection.
Measure more than the visible opening
Write down barrel outside diameter, exposed mounting length, attachment body size and the intended installed position. Check the cavity along the device's full length, including any wider bearing housing or retention feature. A muzzle part passing through the tip hole does not prove clearance deeper inside.
The Harrier and Seagull listings describe a locking piece for use without an MM BCAR. Follow that arrangement's instructions if running the compensator alone. Do not assume a loose compensator should be stabilised by adding tape around an unrelated muzzle device or by clamping onto a dart-contact surface.
Inspect the completed front end
Fit the parts with the blaster unloaded, following the relevant instructions. Check secure retention, concentric alignment and a clear dart path. Stop if the assembly rubs, tilts or damages darts. Test only after fit is established, and compare operation with the same inspected dart batch.
Choose the shortest or longest furniture because it suits your configuration and handling goal. These product dimensions establish fit-related differences; they do not establish a measured accuracy gain from the outer cover. Live pages provide the current colours, package contents and availability.
Frequently asked questions
Does a 34 mm tip hole mean any smaller BCAR fits?
No. Full body clearance, mount engagement and installed position must also work.
Can I run the Harrier or Seagull compensator without a BCAR?
The listings describe an included locking piece for that arrangement. Follow the exact product instructions.
Why does the Seagull BCAR stick out?
The regular compensator listing explicitly describes protrusion with the longest boxed barrel. Confirm a different configuration if full enclosure is your goal.
Products mentioned
- MM Harrier Compensator Short
- MM Harrier Compensator
- MM Seagull Compensator Short
- MM Seagull Compensator
- Firefly Stinger Compensator Mag Cap
- Firefly-specific BCAR200
Related reading
- Worker Harrier Modding Guide
- Worker Seagull Modding Guide
- Monkee Mods Firefly Modding Guide
- Nerf Bcar Muzzle Fit
Sources
Specifications checked 19 October 2026. Manufacturer and product-listing claims are distinguished from editorial buying advice; no new hands-on measurements are claimed here.