Sling attachment guidance for the SIG Sauer M400. Check your exact configuration and both connectors before choosing the McLean Dynamic Retention Sling (DRS). Factory attachment points do not by themselves confirm a direct fit.
Front attachment
M-LOK handguard slot — aftermarket attachment option.
SIG’s operator’s manual states that the M400 TREAD and M400 PRO are fitted with an aluminum handguard with M-LOK attachment points. An M-LOK slot is not itself a sling socket. A sling mount has to be added to the handguard before the front of a sling can connect.
Aftermarket attachment option: a webbing slot is not a QD cup or proof that a hook fits. Confirm the connector and webbing dimensions for this opening.
Rear attachment
Lower receiver QD sling cups — factory attachment point.
The TREAD and PRO manual labels a QD sling cup on both sides of the lower receiver, and SIG lists integrated QD mounts on the lower receiver for the M400-TREAD V2. These take a push-button QD swivel. The same manual shows a further QD cup in the PRO buttstock but not in the TREAD buttstock.
Factory attachment point: a QD cup needs a matching swivel; a socket provision may also need a separate cup. Confirm what is installed and what the hardware includes.
Why this sling on the SIG Sauer M400
An AR spends far more time carried than fired — on a patrol, walking a treeline, working a barricade. The problem a two-point solves badly is the transition: loose enough to shoulder fast, and it swings when your hands are busy. Cinched retention fixes that without a second sling.
The McLean design is a two-point sling with a patented retention system: it cinches tight to hold the rifle against your body hands-free, then releases into a ready position in one pull. It ships in one size and adjusts, so there is no length to choose.
Fitting it
- Clear the rifle. Unload and clear it following the firearm manufacturer’s instructions before fitting any accessories.
- Front: confirm a compatible connector and follow the sling and attachment manufacturer instructions.
- Rear: confirm the matching connector for your stock or rear attachment; do not assume a slot, stud and QD cup are interchangeable.
- Adjust wearing your kit. A setting dialled in without a vest comes up short once it is on.
- Check the transition. It should shoulder without pulling tight across your chest.
Choosing hardware for your configuration
This guide follows SIG’s manual for the M400 TREAD and M400 PRO and its product page for the TREAD V2. Earlier M400 rifles, the SDI and Switchblade models and pistol versions have their own manuals. SIG’s original M400 manual mentions sling attachment points on the lower receiver without naming the type, so inspect an older rifle directly.
Receiver QD cups sit close together at the rear of the rifle. A two-point setup also needs a front connection, which on these models means adding a mount to the M-LOK handguard. Confirm which pieces come with the chosen sling before ordering.
Questions
Does the McLean Dynamic Retention Sling (DRS) fit the SIG Sauer M400?
Compatibility depends on the exact configuration and connectors. Confirm both attachment points and the connector fit before ordering. A factory attachment point does not by itself confirm a direct fit for the McLean sling.
Do I need a snap hook for the front of my SIG Sauer M400?
The McLean sling already carries a front hook. Choose a compatible attachment loop or swivel for that hook, and confirm its clearance and closure on your exact setup before buying additional hardware.
What do I need to buy for the SIG Sauer M400?
Front: Aftermarket attachment option: a webbing slot is not a QD cup or proof that a hook fits. Confirm the connector and webbing dimensions for this opening. Rear: Factory attachment point: a QD cup needs a matching swivel; a socket provision may also need a separate cup. Confirm what is installed and what the hardware includes.
What length sling do I need for the SIG Sauer M400?
There is no length to choose. The sling ships in one size and adjusts, so the same sling covers carry and cinched retention. Set it wearing the kit you actually carry in — a setting dialled in without a vest or heavy coat comes up short once it is on.
Manufacturer and attachment references
Other firearms we have fitment for
SIG Sauer MCX
SIG Sauer MPX
SIG Sauer CROSS
Daniel Defense DDM4 V7
AR Pistol
BCM RECCE-16
Ruger AR-556
Springfield Armory SAINT
Firearm photos: SIG Sauer MCX — Mike Searson, CC BY-SA 4.0 (Background removed with segmentation and reviewed manual mask corrections; subject cropped, proportionally resized and centered on a transparent 1536 × 768 canvas.); SIG Sauer MPX — gar2chan, CC BY 2.0 (Background removed with segmentation and reviewed manual mask corrections; subject cropped, proportionally resized and centered on a transparent 1536 × 768 canvas.); SIG Sauer CROSS — SIG SAUER, Manufacturer image used with permission (Background removed; proportionally resized and centered on a transparent 1536 × 768 canvas.); Daniel Defense DDM4 V7 — Daniel Defense, Used with manufacturer permission (Background removed; image resized and centered.); AR Pistol — Sturm, Ruger & Co., Manufacturer image used with permission (Background removed; proportionally resized and centered on a transparent 1536 × 768 canvas.); BCM RECCE-16 — Bravo Company USA, Used with manufacturer permission (Background removed; image resized and centered.); Ruger AR-556 — Sturm, Ruger & Co., Manufacturer image used with permission (Background removed; proportionally resized and centered on a transparent 1536 × 768 canvas.); Springfield Armory SAINT — Springfield Armory, Manufacturer product image (Background removed with segmentation and reviewed manual mask corrections; subject cropped, proportionally resized and centered on a transparent 1536 × 768 canvas.).
