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Questions & Answers
Why do you not sell the SHIMS for this...or include them with the item if required? Expert Answer

As per the manufacturer: The JMac Customs 4C-12 4-Port Muzzle Brake will include shims as they are required for proper timing.

by Ethan, Gear Expert, March 30, 2023
Can this fit on a rock island armory vrf14 Expert Answer

The JMac Customs 4C-12 4-Port Muzzle Brake for Mobil Choke Shotguns will not work with the RIA VRF14.

by Hunter, Gear Expert, November 30, 2022
Customer Reviews
Helpful Negative Review
Appears unsafe to use by Enthusiast, Verified Owner, April 6, 2025
The choke tube appears smaller than the barrel. Additionally; there should be no space between the barrel and the choke tube, which is created by the timing shims.
2/3 found this helpful
Read 1 Review
Color:
Black
Finish:
Nitride
Fabric/Material:
17-4PH Stainless Steel
Gun Make:
Kalashnikov
Length:
4.7 in
Weight:
5.11 oz

Code: 4VI-BMB-JMC0342-RRD-4C-12-MOBIL

MPN: RRD-4C-12-Mobil

List: $229.95Save 10%
$206.96

  • JMac Customs 4C-12 4-Port Muzzle Brake for Mobil Choke Shotguns, Black Nitride, Black, RRD-4C-12-Mobil
  • Heresy Design Silencer Timing Device, 1/2in Threads, Black, HSTDA
As low as $215.91
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Product Info for JMac Customs 4C-12 4-Port Muzzle Brake for Mobil Choke Shotguns

(A)rm(B)ar(8)inch(R)ise + AB-BA Brace Adapter + SM-4.5 (not assembled).Lightweight and Rigid!Modular Design - Brace/Stock with many mounting optionsIntegrated QD Sling Socket8'' Length7075 T6 AluminumHard-Coat AnodizedOptional Folding Buttplateimage

The AB-BA adapter allows you to install braces like the TailHook from Gear Head WorksAnti-Rotational design7075 T6 AluminumType 3 Hard-coat AnodizeAB-BA Socket Head Screw

AB-BA Anti-Rotation Pin

SM adapters utilize the factory rear trunnions and eliminate the need for additional adapters or folding mechs.This

version of the SM stock/brace adapter is specifically made for 4.5mm

pin folding stocks. 4.5mm trunnions can be found in the SLR 104/106/107

UR/CR/FR. Cheek wield is adjustable by moving the stock/brace up or down

on the adapter.2 height positions7075 aluminumBlack hardcoat anodize finishIncludes mounting bolt for lower hole

Specifications for JMac Customs 4C-12 4-Port Muzzle Brake for Mobil Choke Shotguns:

Manufacturer: JMac Customs
Color: Black
Finish: Nitride
Fabric/Material: 17-4PH Stainless Steel
Gun Make: Kalashnikov
Length: 4.7 in
Weight: 5.11 oz

Features of JMac Customs 4C-12 4-Port Muzzle Brake for Mobil Choke Shotguns

  • 2 QD Sling points Drilled and Tapped for Cheek Risers

Package Contents:

  • JMac Customs 4C-12 4-Port Muzzle Brake for Mobil Choke Shotguns

JMac Customs 4C-12 4-Port Muzzle Brake for Mobil Choke Shotguns Orderable Models

List of Orderable Models

  • JMac Customs 4C-12 4-Port Muzzle Brake for Mobil Choke Shotguns, Black Nitride, Black, RRD-4C-12-Mobil , MPN: RRD-4C-12-Mobil , Code: 4VI-BMB-JMC0342-RRD-4C-12-MOBIL
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Last updated 2026-07-30 UTC.