Century Arms AP53 Stock Kit — Roller-Delayed 5.56 With Both Rear Ends in the Box
The Century Arms AP53 stock kit solves the problem every roller-lock owner runs into. You buy the pistol, you run the brace, and then you spend six months wishing you had a real stock. This bundle skips that step. You get the AP53, the F5 Mfg F5-ACR Gen 3 Stock, and the Cyberarm Light Brace together — so your build is finished the day it clears your FFL.
The Pistol: A Faithful HK53 in 5.56
Century’s AP53 is built by MKE, the same HK-licensed Turkish manufacturer behind the AP5. It is a true roller-delayed blowback design, not a piston gun wearing a costume. The 8.3-inch cold hammer-forged barrel is threaded 1/2×28, so your existing 5.56 can bolts right on. Meanwhile, the stamped steel receiver and Navy-style trigger group give you the handling that made the original HK53 a favorite with the SAS.
AP53 highlights:
- 5.56x45mm NATO, roller-delayed blowback action
- 8.3″ cold hammer-forged barrel, 1/2×28 threaded
- One 30-round HK33-pattern magazines included
- Ambidextrous selector and paddle magazine release
- Fixed front and adjustable diopter rear sights
- Picatinny optic mount and 4-prong flash hider
- 7.2 lbs unloaded, 22.3″ overall length
The Chassis: F5-ACR Gen 3
F5 Mfg cuts the Gen 3 chassis from solid 6061 billet on 5-axis machines, then removes material only where the load path allows. The result is rigid where it counts and light everywhere else. It folds without blocking operation, and it locks up hard in both positions.
Gen 3 adds the piece owners kept asking for: a tool-less adjustable cheek riser. Because the AP53 sits low, that riser is what finally puts your eye behind a red dot or LPVO without a chin weld. In addition, the stock offers seven positions of length adjustment, so it fits a plate carrier or a t-shirt equally well.
The Brace: Cyberarm Light
This kit ships with the Cyberarm Light Brace, not the standard model. That distinction matters on a gun like this one. The Light comes in at 95.75 grams against the standard Cyberarm’s 179.50 grams — a saving of roughly 84 grams.
Three ounces sounds trivial until you handle the AP53. At 7.2 pounds with a heavy steel receiver and a cold hammer-forged barrel, this pistol already wants to sit nose-down. Consequently, every gram you pull off the back end makes the muzzle harder to drive. The Light brace keeps the balance point where a roller gun shoots best. Run it with the strap or without it.
One Chassis, Two Rear Ends
Here is the part that makes the bundle work. The F5-ACR Gen 3 Chassis stays bolted to your firearm. The Cyberarm Light Brace and the Gen 3 Stock both host off that same chassis, so switching between them is a swap at the rear interface — not a teardown, and not a second adapter purchase.
Why Buy Both Together
The federal making tax on short-barreled rifles dropped to $0 on January 1, 2026. Registration did not go away — you still file an ATF Form 1, submit prints, and wait for approval before installing a stock. But the cost barrier is gone, and recent eForm 1 approvals have been measured in weeks rather than months.
So the smart play is simple. Shoot it as a braced pistol today. File your Form 1 tonight. Then swap to the Gen 3 stock the week your stamp lands, without placing a second order or fighting a backorder queue. Check your state law first, since several states restrict SBRs regardless of federal status.
This firearm ships to a licensed FFL. Magazine capacity restrictions apply in some states. Nothing here is legal advice — verify current federal and state requirements at atf.gov before configuring your firearm.
