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Compact Action Bumper Exchange

At CMMG safety and reliability are our top priorities. As part of our ongoing commitment to quality, we are issuing a voluntary part exchange for a specific component used in the DISSENT firearm.

  • Component – Bumper used in the Compact Action assembly
  • Issue Identified – We have identified isolated instances of failure with the bumper. We have changed our manufacturing process of the part for superior durability and wear resistance after rigorous performance testing.
  • Firearms Affected – Mk57 and Mk4 DISSENT firearms and upper groups in these calibers: 5.7x28mm, 22 ARC, 300BLK, 338 ARC, 350 Legend, 5.56x45mm, 6.5 Grendel, and 6mm ARC.
    • Mk3, Mk47, and 9mm/.45 ACP Mk4 DISSENT upper groups are NOT affected. Mk4 DISSENT bumpers will NOT work with Mk3, Mk47, or 9mm/.45 ACP Mk4 BCGs.
  • Please compare the bumper on your DISSENT bolt carrier group to the identification guide below to verify if your DISSENT is affected.
  • If you own an affected firearm, please notify our customer service team using the contact form at the bottom of this page.

We sincerely apologize for any inconvenience and appreciate your continued trust in CMMG.


Location:

The DISSENT bumper can be found at the rear of the Compact Action bolt carrier group. To remove the bumper, press the front of the bumper up from between the action springs and the tail down from the rear to pivot the bumper out of the BCG.

Identification:

Affected bumpers can be identified by the vertical hole extending through the top and bottom of the bumper. The updated injection molded bumpers do NOT have a hole through the top and bottom and can also be identified by the four square mold relief indentations along the left and right side of the bumper.


What To Do:

If your Mk4 DISSENT bolt carrier group has one of the affected bumpers, fill out the contact form at the bottom of this page with all required information. A replacement bumper along with a pre-paid return envelope will be mailed to you at no cost. Upon receipt of the replacement bumper(s), please send the original 3D printed part back to CMMG in the included pre-paid envelope.


Questions:

For further questions please contact CMMG Customer Service at: customerservice@cmmg.com


Bumper Exchange Form