Best 1913 Stocks: Folding, Collapsible & Buffer-Tube Adapters header image
Gear
May 8, 2026
Best 1913 Stocks: Folding, Collapsible & Buffer-Tube Adapters

Universal 1913 Picatinny stocks ranked for SBR-configured AR pistols, PCCs, and PDW hosts. Magpul UCS, Black River ACX 1913 Stock, Strike Industries FSA Dual and Single Folder, the SIG Sauer 1913 Folding Knuckle buffer-tube path, and the budget polymer FSA compared by lockup, adjustability, and weight.

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

Post-OBBBA the federal NFA tax on SBRs is zeroed and eForm 1 approvals are running a couple of days, so the 1913 stock ecosystem just became the default answer for serious PDW and PCC builds. This guide ranks the universal 1913 Picatinny stocks shipping in 2026: the Magpul UCS, Black River MFG ACX 1913, Strike Industries FSA Dual and Single Folder, the SIG Sauer 1913 Folding Knuckle (buffer-tube adapter path), and the budget Polymer FSA. If you are pistol-configured and not filing an SBR, see our best 1913 braces guide instead.

By AB|Last reviewed May 2026

Why a 1913 Stock Beats a Brace in 2026

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.

Top 6 Best 1913 Stocks (2026 Rankings)

Universal 1913 Picatinny stocks for SBR-configured AR pistols, PCCs, and PDW hosts. Ranked by lockup, adjustability, weight, and value.

1

Magpul UCS Universal Carbine Stock (1913)

Best Overall 1913 Stock

$208.75
View at OpticsPlanet
  • +Most adjustable 1913 stock on the market
  • +Cheek risers solve high-optic-deck builds
  • +Reversible fold is a Magpul-only feature in this category
  • 18 oz, heavier than minimal 1913 folding stocks
  • Mid-tier price for a stock vs a brace alternative
2

Black River MFG ACX 1913 Collapsible Stock

Best All-Aluminum 1913 Stock

$245.99
View at OpticsPlanet
  • +All-metal load-bearing parts for serious duty use
  • +Tail hook gives a real index point on a 1913 stock
  • +9 LOP positions, more granular than most fold stocks
  • Collapsible only, does not fold flat
  • Carbon-fiber color variants run ~$310
3

Strike Industries FSA Dual Folder Stock (1913)

Best Bidirectional-Fold 1913 Stock

$187.95
View at OpticsPlanet
  • +Only 1913 stock that folds either side without parts swap
  • +Compact folded profile
  • +All-aluminum body construction
  • Fixed length, not collapsible
  • $20 more than the Single Folder Stock
4

Strike Industries FSA Single Folder Stock (1913)

Best Lightweight 1913 Folding Stock

$159.95
View at OpticsPlanet
  • +Cheapest steel-hinge universal 1913 stock
  • +Field-proven chassis from the Kuna factory match
  • +Light enough for compact PDW builds
  • Left-fold only
  • Fixed length, no LOP adjustment
  • Polymer end pieces vs all-aluminum competitors
5

SIG Sauer 1913 Interface Folding Knuckle Stock Adapter

Best Buffer-Tube Adapter Path

$110.99
View at OpticsPlanet
  • +Bridges 1913 hosts to the entire AR carbine stock catalog
  • +Both mil-spec and commercial buffer tube threads supported
  • +Stack-cheap path if you already own an AR stock
  • Buffer tube and stock are sold separately
  • Total assembly is longer and heavier than a dedicated 1913 stock
  • Adds a second mating surface in the lockup
6

Strike Industries Polymer FSA Folding Stock (1913)

Best Budget 1913 Stock

$89.95
View at OpticsPlanet
  • +Half the price of the steel-hinge FSA Single Folder
  • +Ambidextrous fold without buying a different SKU
  • +Lightest 1913 folding stock available
  • Flexes more than steel-hinge alternatives under cheek pressure
  • Polymer construction throughout
  • No LOP or cheek-riser adjustment

Purchasing through these links may generate a commission for Rifle Configurator at no extra cost to you.

Dedicated 1913 Stock vs Buffer-Tube Adapter Path

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.

Pick a Dedicated 1913 Stock if

  • +You want the shortest, lightest possible assembly
  • +You need a high-deck cheek riser (Magpul UCS)
  • +You need bidirectional fold (FSA Dual Folder)
  • +You want 9-position collapse (Black River ACX)

Top picks: Magpul UCS, Black River ACX 1913, Strike Dual Folder

Pick the Buffer-Tube Adapter if

  • +You already own an AR carbine stock you love
  • +You want a Magpul STR or CTR cheek weld
  • +You want one common stock across all your hosts

Pair: SIG 1913 Folding Knuckle + your favorite AR carbine 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.

1913 Stock Spec Comparison

ModelMechanismLOPCheek RiserWeightPrice
Magpul UCSReversible fold + collapse7.6 - 10.6 in0.50, 0.75 in (incl.)18 oz$209
Black River ACX 1913Collapse only9 positionsTail hook~16 oz$246
SI FSA Dual FolderBidirectional foldFixedNone9.9 oz$188
SI FSA Single Folder StockLeft foldFixedNone10.75 oz$160
SIG 1913 Folding KnuckleAdapter + your AR stockPer AR stockPer AR stock~6 oz (knuckle)$111
SI Polymer FSA StockAmbidextrous foldFixedNone~9 oz$90

Mounting: Native 1913 Hosts vs Adapter Hosts

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.

Frequently Asked Questions

What is a 1913 stock?
A 1913 stock mounts to a MIL-STD-1913 Picatinny rail at the rear of the host receiver instead of a buffer tube. The interface is universal: any host that ends in a 1913 rear rail (Sig MPX, Sig MCX, Stribog with factory adapter, CZ Scorpion with HBI 1913 adapter, Springfield Kuna, B&T APC9 and GHM9, AR pistols with a 1913 endplate) accepts the same stock. A 1913 stock requires an SBR-configured host because the rifle buttplate makes it not pistol-legal. For pistol-config builds use a 1913 brace instead.
Which is the best 1913 stock overall?
The Magpul UCS ($209) is the best 1913 stock overall. It is the only universal 1913 stock with a reversible left-or-right hinge, includes 0.50-inch and 0.75-inch cheek risers in the box, and has a half-slot height adjustment on the 1913 clamp for fine-tuning vertical position. LOP runs 7.6 to 10.6 inches across a 3-inch range. Weight is 18 ounces. For all-aluminum durability the Black River MFG ACX 1913 Stock ($246) is the alternative, and for the lightest steel-hinge pick the Strike Industries FSA Single Folder Stock ($160) is the value answer.
Stock or brace, post-OBBBA in 2026?
Post-OBBBA the federal NFA tax on SBRs is zeroed and ATF eForm 1 SBR conversions are running a couple of days, not 6-12 months. For most builders the math now favors a 1913 stock because you get cheek-riser adjustment, longer LOP range, and a real buttplate without the soft brace cuff. State law still varies. Check your state before filing the eForm. For pistol-config builds where you cannot or will not file an SBR, see our 1913 braces guide.
Can I use a regular AR carbine stock on a 1913 host?
Yes, with a 1913-to-buffer-tube adapter. The SIG Sauer 1913 Interface Folding Knuckle ($111) mounts on any 1913 rear rail and presents a standard mil-spec or commercial-spec carbine buffer tube thread, which accepts any AR carbine stock (Magpul CTR, B5 Bravo, BCM Gunfighter Mod 0, B5 SOPMOD) or buffer-tube pistol brace. The adapter folds left for compact transport. The combined assembly (knuckle + buffer tube + stock) is longer and heavier than a dedicated 1913 stock, but lets you reuse an AR stock you already own.
Folding 1913 stock vs collapsible 1913 stock?
Folding 1913 stocks (Magpul UCS, Strike Industries FSA Single and Dual Folder, Strike Industries Polymer FSA) hinge against the receiver for compact transport but maintain a fixed extended length. Collapsible 1913 stocks (Black River MFG ACX 1913) telescope across multiple LOP positions but do not fold flat. Pick folding for storage and vehicle transport. Pick collapsible for shooters of different sizes or for switching between bare arms and a plate carrier. The Magpul UCS does both: it folds AND adjusts LOP across a 3-inch range.
Will a 1913 stock fit my AR pistol or rifle?
Only if the host has a 1913 Picatinny endplate (also called a 1913 EAR) in place of the buffer tube. Most AR rifles and AR pistols ship with a buffer tube and do not accept 1913 stocks directly. Convert an AR by installing a 1913 endplate (KAK Industry, Mean Arms), at which point any 1913 stock in this guide will mount. Conversely, the SIG Sauer 1913 Folding Knuckle goes the OTHER direction: it lets a 1913 host accept a buffer-tube stock.
Which 1913 stock supports high optic decks (LPVO, prism, NVG)?
The Magpul UCS ($209) is the strongest pick for high-mount optic decks. It ships with two cheek risers (0.50 inch and 0.75 inch) and a half-slot 1913 clamp that lets you raise or lower the stock body relative to the host's rear rail. Without a riser, low-profile fold stocks like the FSA Single Folder Stock or Polymer FSA give you a thin cheek surface that does not consistently match a 1.93-inch LPVO mount or a 2.26-inch NVG mount. For comfort under a tall optic, run a UCS or pair the SIG 1913 Knuckle with a Magpul STR or B5 SOPMOD that includes its own cheek-riser geometry.
What hosts use a 1913 rear interface from the factory?
Sig MPX (all variants), Sig MCX (Virtus, Spear LT, Rattler), Sig Rattler, Rock River LAR-PDS, Springfield Kuna, B&T APC9 and GHM9, B&T APC9K, and most modern PDW-class hosts ship with a 1913 rear rail directly. CZ Scorpion EVO 3 S1/S2/3+ requires the HB Industries 1913 adapter. Grand Power Stribog accepts the factory 1913 adapter (under $40). AR pistols and rifles require a 1913 endplate (KAK or Mean Arms) installed in place of the buffer tube. AKs require a JMac Customs RSA, Bonesteel, or SLR Rifleworks adapter.