Short answer: buy M-LOK. It attaches accessories straight to slots in the handguard, Magpul licenses it free to any maker, and in the Navy's 2017 NSWC Crane test it beat KeyMod on repeatability (1.3 vs 4.9 MOA average shift) and in drop tests (all M-LOK accessories stayed attached, one of three KeyMod did). Picatinny (MIL-STD-1913) is still the standard for optics and clamp-on accessories, so most M-LOK builds add short Picatinny sections where needed.
M-LOK vs KeyMod vs Picatinny at a glance
| M-LOK | KeyMod | Picatinny (MIL-STD-1913) | |
|---|---|---|---|
| Origin | Magpul, released 2014 (Crane says early 2015) | VLTOR, released 2012 | Standardized in 1995 |
| How it attaches | T-nuts pass through a slot and turn 90 degrees to lock | Nut passes through the round end of a keyhole, slides forward and is tightened | Accessory clamps onto a raised rail with cross slots |
| Crane repeatability (average shift) | 1.3 MOA (0.0 to 6.6) | 4.9 MOA (0.2 to 14.6) | Not tested |
| Crane drop test | All 3 accessories stayed attached (2 slid rearward) | 1 of 3 stayed attached; 2 detached | Not tested |
| Licensing | Free licence from Magpul | Released as a standard platform | Military standard |
| Best for | Most new handguards and accessories | Existing KeyMod rifles | Optics, and lights or grips on a quad rail |
Test figures are from NSWC Crane's "KeyMod vs. M-LOK Modular Rail System Comparison" (May 2017, approved for public release). Crane tested 18 handguards: three KeyMod and three M-LOK from each of Aero Precision, Midwest Industries and Seekins. It says the tests were built for a direct comparison, not to simulate exact field conditions. M-LOK details are from Magpul.
What the NSWC Crane test found
- Repeatability: after removing and refitting a rail with a laser on it five times, KeyMod averaged 4.9 MOA of point-of-aim shift and M-LOK 1.3 MOA, a 73% improvement. Crane also found M-LOK depends on correct installation: fitted at the wrong angle in the slot, it averaged 18.4 MOA.
- Endurance and rough handling: both systems survived 10,200 simulated full-auto rounds and the rough-handling loads with no failures or loose fasteners.
- Drop test: from 5 feet onto steel, every M-LOK accessory stayed attached, though two slid rearward in their slots. Only one of three KeyMod accessories stayed on, and the KeyMod handguards cracked between slots.
- Pull-off load: M-LOK's average failure load was over three times KeyMod's, and every M-LOK test failed at the light mount rather than at the handguard.
How to install M-LOK accessories correctly
Crane's 18.4 MOA result shows why this matters. Magpul's tips sheet says to:
- Set the T-nut gap slightly more than the thickness of the handguard wall.
- Seat the accessory flush in the slot, then push it forward and to one side before tightening, for repeatability.
- Check the T-nut turns the full 90 degrees into the locked position.
- Torque to 35 in-lb for metal accessories on a metal handguard, and 15 in-lb whenever the accessory or handguard is polymer. Magpul says these are limits, not minimums.
M-LOK rail covers
Magpul makes two kinds. The Type 1 is a flexible 9.5 inch strip that covers six slots and can be cut to length. The Type 2 is a two-piece snap-in cover, one per slot, standing just over 1/8 inch above the rail; Magpul says Type 2 does not fit its MOE M-LOK, MOE SL or SGA forends.
M-LOK rail covers and sections, with today's prices
Lowest price across the stores we track:
Magpul M-LOK Rail Cover Type 1
Pros
- Flexible 9.5 in strip, covers six slots
- Cut to any length
Cons
- Plain strip, no snap-in lock
Long cover
Magpul M-LOK Rail Cover Type 2
Pros
- Snap-in, one slot each
- About 1/8 in above the rail
Cons
- Does not fit Magpul MOE M-LOK, MOE SL or SGA forends
Snap-in cover
Ergo Wedgelock M-LOK rail cover
Pros
- M-LOK compatible polymer cover
- 6.25 in long
Cons
- Few published specs
Alternative
Magpul M-LOK polymer Picatinny rail, 11 slots
Pros
- 4.9 in Picatinny section for M-LOK
- For lights, grips and bipods
Cons
- Polymer: Magpul's torque limit is 15 in-lb
Picatinny section
Geissele Picatinny rail for M-LOK handguards, 5 slots
Pros
- Short Picatinny section for M-LOK
Cons
- Costs more than the Magpul polymer section
Aluminum section
M-LOK, KeyMod and Picatinny handguards, with today's prices
BCM MCMR 13 in handguard (M-LOK)
Pros
- Free-float, M-LOK slots
- 13 in for mid-length or rifle gas
Cons
- Higher price than drop-in polymer
M-LOK
Magpul MOE M-LOK handguard, carbine
Pros
- Drop-in polymer handguard with M-LOK slots
- Low price
Cons
- Not free-float; polymer torque limit
Budget M-LOK
BCM KMR Alpha 15 in KeyMod handguard
Pros
- Free-float, KeyMod slots
Cons
- Far fewer KeyMod parts in stock than M-LOK
KeyMod
BCM QRF 12 in Picatinny handguard
Pros
- Free-float with full Picatinny rails
Cons
- Full-length rails you may not need
Picatinny
How to choose
- New build: an M-LOK free-float handguard, with Picatinny sections only where you need them. Size it to your gas system with our handguard length guide.
- Already on KeyMod: it passed Crane's endurance and rough-handling tests, but in our catalog M-LOK parts outnumber KeyMod about 20 to 1 (653 vs 32 in stock, October 2026).
- Optics: they mount on the Picatinny rail on top of the upper and handguard.
- Polymer handguards such as the Magpul MOE use the lower 15 in-lb torque limit.
Compare every AR-15 handguard by price, and plan the build in the AR-15 builder. See also our accessories checklist.
Frequently asked questions
Is M-LOK better than KeyMod?
In NSWC Crane's 2017 test, yes: 1.3 vs 4.9 MOA average point-of-aim shift, and all M-LOK accessories stayed attached in drop tests against one of three KeyMod. Both passed endurance and rough handling.
Can I mount Picatinny accessories on an M-LOK handguard?
Yes, with an M-LOK Picatinny rail section, such as Magpul's 4.9 inch 11-slot polymer rail.
What torque for M-LOK screws?
Magpul says 35 in-lb for metal accessories on metal handguards and 15 in-lb when either part is polymer. They are limits, not minimums.
Is M-LOK free to use?
Magpul released M-LOK in 2014 as a free licensed platform, so any maker can build to it.
What are M-LOK rail covers for?
They cover empty slots for grip and protection. Magpul's Type 1 is a cuttable 9.5 inch strip; Type 2 snaps into one slot.
Is KeyMod dead?
It is far less common: of the in-stock handguards and rails in our catalog in October 2026, 653 are M-LOK and 32 KeyMod. KeyMod rifles still work; Crane found no failures in its endurance and rough-handling tests.
