M249 hop-up chamber

• For M249/MINIMI by A&K, P&J, CA
• Precise hop-up adjustment– the regulator wheel has 360° setting range
• The direction of hop-up regulation is visibly marked.
• State-of-the art design of the bucking's lip fit on the inside of the chamber – successfully tested with most of the buckings available on the market
• Designed for AEG hop-up buckings with standard lip length (e.g. Systema). To adjust the chamber for use with buckings with longer lip length, it's possible to use enclosed washers – read more on the lip length issues in our article.
• The adjustment of the chamber's clearance against gearbox's opening is done with the enclosed o-rings (two sizes).
• Vertically seated pressure bar – works great with Maple Leaf hop-up buckings
• A groove in the top of the hop-up chamber allows for fixation inside the gun's outer barrel housing.
• The hop-up chamber can also be fixated inside the gun's body by using the enclosed grub screw.
• The pin for mounting of the chamber into the feed assembly is replaceable – if needed, it is possible to use a longer pin for a better fit
• Made of EN AW 7075-T6 aircraft-grade duralumin with proven H+PTFE surface finish
• Made in the Czech Republic

Package contents

• Hop-up chamber
• Hop-up pressure bar regulation ring
• 1 pressure roller
• 2 pcs o-rings for securing of the regulator ring (9×1,5 mm)
• 2 pcs o-rings for adjusting the clearance of the chamber against the gearbox opening (sizes 6×1 mm and 9×1 mm)
• 2 pcs spacer sleeves for hop-up bucking lip (0.1 + 0.2 mm)
• 4 pcs grub screws for fixation of the gun's barrel inside the hop-up chamber (2 pcs M3×5 + 2 pcs M3×4 – fits the boltholes located inside the groove on top and bottom of the chamber)
• A grub screw for fixation of the hop-up chamber inside the outer barrel housing (M3×12)
• A longer replacement pin for mounting of the chamber inside the feed assembly

A perfect fit for the bucking's lip

The correct shape of the chamber's bucking lip seat is critical for the issue-free operation and optimal performance of AEGs. That's why the development of the optimal seat geometry is our top priority and why we have invested dozens of hours into testing and making adjustments.

The result is a universal geometry that fits almost all hop-up buckings available on the current market. The testing was conducted with more than 30 types of hop-up buckings. The seat is designed for the issue-free operation and good sealing when used with the AEG standard lip length buckings. In case you need to use a bucking with a longer lip, you can add the spacer sleeve enclosed in the package. You can read more on this topic in ourarticle.

Great emphasis is placed on the manufacturing precision and the surface quality of not only this integral detail of every hop-up chamber, but also of all other details of this product.

Innovative mounting of the chamber

The second important factor, which affects the performance and function of the AEG is the correct mounting of the hop-up chamber in between the outer barrel housing and the gearbox. A chamber misaligned from the imaginary axis drawn through the centers of the piston head, nozzle, chamber, and barrel causes drops in performance, feeding issues, and can even cause airflow obstruction problems. You can read more about airflow obstruction problems in our article.
The correct fitting of the hop-up chamber against the gearbox opening and therefore the correct axial alignment can be adjusted with the enclosed various-sized o-rings.

To ensure precise shooting and reliable feeding, it is necessary to prevent the chamber from rotating on its axis while mounted. The chamber has a standard mounting by pin on the bottom of the chamber, which fits into a groove on the feeding well of the gun's body and prevents the chamber from rotating. The pin can be replaced with a longer version in case it doesn't fit well into the groove (e.g.. if the pin is too short). The longer replacement pin is enclosed in the package.

An alternative option of preventing the chamber from rotation is to use a thread in the upper part of the chamber near the hop-up regulator ring. With the enclosed M3×12 grub screw, the chamber can be fixed against the groove in the midsection of the weapon's body. This option is especially suitable in case you don't want to use the quick takedown of the outer barrel – if you decide to use this option, it's necessary to always remove the fixation grub screw before quick removal of the outer barrel.

As a third option (f.e. for easy access to your battery in the handguard), you can use a groove near the top part of the chamber and fix the chamber directly into the outer barrel housing. Although it is necessary to modify the seat first, the modification allows fixation against rotation of the chamber without obstructing the axial movement in the direction of the pressure spring placed against the face of the gearbox. This preserves the quick barrel removal function - this movement is necessary for locking of the outer barrel into the weapon's body.