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Forward Controls Design
The Forward Controls Design A5 Castle Nut in Olive Drab Green is a precision-engineered receiver extension fastener built specifically for the Vltor A5 buffer tube system. If you're running an A5-compatible setup and want a castle nut that's engineered to handle the longer receiver extensions without sacrificing stock collapse, this is the part that bridges that gap. FCD designed the CN5F to be 0.1" longer than their standard castle nut while maintaining full backward compatibility with both Vltor's RE-A5 and FCD's RE5F receiver extensions—a careful balance that lets even the longest carbine stocks fully collapse without binding.
The real value here is in the details. FCD took feedback from years of working with castle nuts and made purposeful improvements: the staking notches are angled at 30 degrees instead of the standard 45, resulting in deeper, longer engagement surfaces (25% longer than TDP spec) and a fourth notch added to the rotation for more staking location options. That means you get three visible notches available at any time, giving you flexibility in where you choose to stake. The wrench side features coarse serrations that make installation easier—a small feature that adds up when you're doing the work yourself.
Built from 4140 PH steel and finished in hard black nitride with OD Green Cerakote, this castle nut is billet machined and made entirely in the USA. At just 0.51 ounces, it's a straightforward, robust component designed to stay put once staked per TM. It's the kind of part that doesn't grab attention but absolutely earns respect through thoughtful engineering and real-world usability.
| Material | 4140 PH Steel | |
| Finish | Black Nitride with OD Green Cerakote | |
| Weight | 0.51 oz | |
| Staking Notches | 4, angled 30 degrees | |
| Design | Billet Machined | |
| Made in | USA |
Yes, the CN5F will function on standard TDP spec length receiver extensions. However, because of its extended length, carbine stocks may not fully collapse on standard REs—the additional nut length can prevent full retraction. It's specifically engineered to allow full collapse on Vltor RE-A5 and FCD RE5F receiver extensions.
The CN5F is 0.1" longer than FCD's standard CNF to accommodate A5-compatible systems. It also features deeper staking notches (angled at 30 degrees instead of 45), four notches instead of three for more staking options, and coarse serrations on the wrench side for easier installation. These refinements improve both usability and long-term security when properly staked.
You'll need a castle nut wrench or armorers' wrench to install and time the nut on your receiver extension. The coarse serrations on the wrench side are designed to assist with rotation during installation. Once installed, the nut should be staked in two locations per TM specification to prevent loosening.
The CN5F is specifically designed for Vltor A5 systems and will work with both Vltor's RE-A5 and FCD's RE5F receiver extensions, allowing full stock collapse. If you're uncertain about your specific A5 compatible receiver extension variant, FCD maintains detailed information on their website regarding RE-A5, RE5F, and RE10/A5SR compatibility differences.
Forward Controls Design
The Forward Controls Design A5 Castle Nut in Olive Drab Green is a precision-engineered receiver extension fastener built specifically for the Vltor A5 buffer tube system. If you're running an A5-compatible setup and want a castle nut that's engineered to handle the longer receiver extensions without sacrificing stock collapse, this is the part that bridges that gap. FCD designed the CN5F to be 0.1" longer than their standard castle nut while maintaining full backward compatibility with both Vltor's RE-A5 and FCD's RE5F receiver extensions—a careful balance that lets even the longest carbine stocks fully collapse without binding.
The real value here is in the details. FCD took feedback from years of working with castle nuts and made purposeful improvements: the staking notches are angled at 30 degrees instead of the standard 45, resulting in deeper, longer engagement surfaces (25% longer than TDP spec) and a fourth notch added to the rotation for more staking location options. That means you get three visible notches available at any time, giving you flexibility in where you choose to stake. The wrench side features coarse serrations that make installation easier—a small feature that adds up when you're doing the work yourself.
Built from 4140 PH steel and finished in hard black nitride with OD Green Cerakote, this castle nut is billet machined and made entirely in the USA. At just 0.51 ounces, it's a straightforward, robust component designed to stay put once staked per TM. It's the kind of part that doesn't grab attention but absolutely earns respect through thoughtful engineering and real-world usability.
| Material | 4140 PH Steel | |
| Finish | Black Nitride with OD Green Cerakote | |
| Weight | 0.51 oz | |
| Staking Notches | 4, angled 30 degrees | |
| Design | Billet Machined | |
| Made in | USA |
Yes, the CN5F will function on standard TDP spec length receiver extensions. However, because of its extended length, carbine stocks may not fully collapse on standard REs—the additional nut length can prevent full retraction. It's specifically engineered to allow full collapse on Vltor RE-A5 and FCD RE5F receiver extensions.
The CN5F is 0.1" longer than FCD's standard CNF to accommodate A5-compatible systems. It also features deeper staking notches (angled at 30 degrees instead of 45), four notches instead of three for more staking options, and coarse serrations on the wrench side for easier installation. These refinements improve both usability and long-term security when properly staked.
You'll need a castle nut wrench or armorers' wrench to install and time the nut on your receiver extension. The coarse serrations on the wrench side are designed to assist with rotation during installation. Once installed, the nut should be staked in two locations per TM specification to prevent loosening.
The CN5F is specifically designed for Vltor A5 systems and will work with both Vltor's RE-A5 and FCD's RE5F receiver extensions, allowing full stock collapse. If you're uncertain about your specific A5 compatible receiver extension variant, FCD maintains detailed information on their website regarding RE-A5, RE5F, and RE10/A5SR compatibility differences.
