The easiest solution is just get a Compmag. Apparently there are more solutions that I was not aware of:
1. MagLatch F.N.G.R. Kit
- Status: In active production.
- Availability: MagLatch still manufactures their platform-specific Sig Sauer MCX/Spear LT Fixed Magazine Kit. It remains a highly sought-after solution because it preserves the rifle's clean exterior aesthetic by hiding the locking mechanism entirely inside the receiver. [1, 2]
2. CompMag (Gen 3 AR-15)
- Status: In active production.
- Availability: CompMag continues to mass-produce the AR-15 CompMag Gen 3. It is a staple for California and New York compliance. It remains widely available across major online compliance distributors and directly from their website. [1, 2, 3]
3. Patriot Mag Release (PMR) & Bullet Button Adaptations [
1]
- Status: In active production / widely distributed.
- Availability: Various manufacturers still produce Patriot Mag Release Kits and modified legal magazine locks. Specialty compliance retailers rely heavily on these components to convert factory-standard Spear LTs into state-legal configurations before shipping them to restricted areas. [1]
4. Jerry's Firearms JFS Systems
- Status: In active production.
- Availability: Jerry’s Firearms Warehouse actively builds and sells complete, modified NY/CA Compliant Fixed Mag Sig Spear 5.56 and large-frame .308/6.8 Spear variants. They use their proprietary, precision-machined internal components to facilitate top-loading when the action is broken open. [1, 2, 3]
Apparently you can even use a Gen 4 AR Maglock & Kingpin:
The absolute best "fast-detach" system for the MCX Spear LT is a modified
AR Maglock Gen 4 paired with an AR Maglock KingPin.
This combination allows you to drop the magazine instantly by pushing a button to split the action a mere fraction of an inch, bypassing the cumbersome top-loading or side-loading processes. [
1]
Why the Gen 4 + KingPin Setup Rules the Spear LT
- Maintains "Normal" Reloading: Pushing the KingPin rear takedown pin separates the receivers slightly. This frees the AR Maglock (arm) to clear the upper, letting you drop the magazine using your standard mag release button. Pushing the receivers shut automatically locks it back up.
- Fixes the Ambi-Control Clearance Issue: Unlike older versions, the AR Maglock Gen 4 features an adjustable arm set screw. This allows you to space the locking arm outward to clear the wider, non-mil-spec ambidextrous lower receiver and bolt-catch fencing unique to the Sig Spear LT platform.
- Clears Double Feeds Instantly: Because the system allows the magazine to drop even when the bolt is locked back (a critical flaw in many other fixed-mag designs), you can safely and quickly clear complex ammunition malfunctions. [1, 2, 3]
Critical Installation Note for the Spear LT
Even though the AR Maglock Gen 4 is highly adjustable, the Spear LT upper receiver flares out wider than a standard AR-15. To achieve flawless operation, you or a gunsmith will typically need to
lightly file or shave down the back of the Maglock arm. This ensures it sits perfectly flush in the gap between the upper and lower receiver without marring your rifle's finish. [
1,
2]
The Best "No-Modification" Detach Alternative
If you refuse to file down a mechanical arm, the next best option is the
MagLatch F.N.G.R. Kit paired with an
AR Maglock KingPin. [
1,
2]
- The Workflow: You pull the KingPin to crack the action open, manually pull the magazine out from the bottom, and push a new one in.
- The Advantage: It requires zero physical modification or filing to the rifle, keeping the Spear LT's exterior completely stock. [, 2]
What caliber it it?
