Best 1913 Stocks: Folding, Collapsible & Buffer-Tube Adapters

A 1913 stock mounts to a MIL-STD-1913 Picatinny rail at the rear of the host receiver and ends in a rifle buttplate, which makes it SBR-only. Pre-OBBBA that meant filing a Form 1, paying $200, and waiting six to twelve months. Post-OBBBA the tax is zero, eForm 1 approval is running days, and the only remaining question is your state law.

The 2026 reality: stocks deliver longer extended LOP, real cheek risers, and a rifle buttplate that braces structurally cannot match. The Magpul UCS includes 0.50-inch and 0.75-inch cheek risers in the box for shooters running LPVO mounts and NVG-height optic decks. The Black River ACX 1913 collapses across 9 positions, more than any folding 1913 brace ships with. The Strike Industries FSA Dual Folder Stock is the only bidirectional-fold 1913 stock currently shipping. None of these features exist on the brace side of the catalog.

Use the rifle builder to spec a 1913-equipped host, or the catalog to browse every 1913 stock and brace shipping today. For PDW- class build context, see the PDW pistol guide.

A dedicated 1913 stock (Magpul UCS, Black River ACX, FSA Dual Folder) is shorter, lighter, and has only one mating surface between stock and host. The buffer-tube adapter path (SIG Sauer 1913 Folding Knuckle plus a mil-spec carbine tube plus your AR stock of choice) gives you the cheek weld of any AR carbine stock, but adds a second mating surface and roughly two extra inches of length over a comparable 1913 stock.

Cost math: SIG 1913 Knuckle ($111) + DoubleStar mil-spec carbine buffer tube ($33) + Magpul CTR stock ($65) lands at roughly $209, the same total as a Magpul UCS. The UCS adds the cheek risers and reversible fold; the buffer-tube path gives you the AR carbine stock cheek weld and reuse of an existing stock. Pick on stock preference, not price.

Native 1913 hosts (Sig MPX, Sig MCX, Sig Rattler, Rock River LAR-PDS, Springfield Kuna, B&T APC9, B&T GHM9) accept any 1913 stock in this guide directly. No adapter, no fitment check beyond confirming the rear rail length. The Magpul UCS half-slot clamp adjustment requires a rail with at least three usable slots; every other stock in this guide needs only two.

Adapter hosts need a one-time install before any 1913 stock will mount. The CZ Scorpion EVO 3 takes the HB Industries 1913 Stock Adapter (~$89) for the S1/S2 generation; the Scorpion 3+ uses a different HBI adapter due to the new trunnion geometry. The Grand Power Stribog accepts the Global Ordnance Stribog 1913 Brace Adapter (~$40) directly on the factory rear interface. AR pistols and AR rifles need a 1913 endplate (KAK Industry or Mean Arms) installed in place of the buffer tube. AKs need a JMac Customs RSA-AKM, Bonesteel, or SLR Rifleworks 1913 adapter. For Stribog builders see the Stribog accessories guide; for Kuna builders the Springfield Kuna upgrades guide; for Scorpion builders the CZ Scorpion upgrades guide.