AR-15 Handguard Length Chart
Handguard length is measured from the front of the upper receiver. Pick it by two things on the barrel: how long the barrel is, and where the gas block sits.
The Short Answer
- A rail shorter than the barrel leaves the muzzle device out front; a rail as long as the barrel or longer covers part of the device, a popular look. Install the device before the rail.
- To cover the gas block, the rail has to reach past it: about 4.5" from the receiver on pistol gas, 7.5" on carbine, 9.5" on midlength and 12.5" on rifle gas. A shorter rail works but leaves the block showing.
- A common pairing is a 16" midlength barrel with a 13" to 15" rail.
- Drop-in handguards must match the gas system length and need an A2 front sight base to hold them.
Handguard and Barrel
Every handguard we list against each barrel length and gas system. "+2.0" past" means the rail runs that far past the muzzle, "At muzzle" means it ends right at it, and "Block shows" means the gas block sits outside the rail. All of those fit.
| 7.5" pistol | 9" pistol | 10.3" carbine | 11.5" carbine | 16" carbine | 16" mid | 16" pistol | 18" rifle | 20" rifle | |
|---|---|---|---|---|---|---|---|---|---|
| Midwest Industries Combat Rail 7" M-LOK | At muzzle | Fits | Block shows | Block shows | Block shows | Block shows | Fits | Block shows | Block shows |
| Aero Precision ATLAS S-ONE 9.2" M-LOK | +1.7" past | +0.2" past | Fits | Fits | Fits | Block shows | Fits | Block shows | Block shows |
| Midwest Industries Combat Rail 9.25" M-LOK | +1.8" past | +0.3" past | Fits | Fits | Fits | Block shows | Fits | Block shows | Block shows |
| Bravo Company MCMR-10 M-LOK Rail | +2.5" past | +1.0" past | At muzzle | Fits | Fits | Block shows | Fits | Block shows | Block shows |
| Bravo Company MCMR-13 M-LOK Rail | +5.5" past | +4.0" past | +2.7" past | +1.5" past | Fits | Fits | Fits | Block shows | Block shows |
| Palmetto State Armory 13.5" Lightweight M-LOK Rail | +6.0" past | +4.5" past | +3.2" past | +2.0" past | Fits | Fits | Fits | Fits | Fits |
| Geissele MK16 Super Modular Rail 13.5" M-LOK | +6.0" past | +4.5" past | +3.2" past | +2.0" past | Fits | Fits | Fits | Fits | Fits |
| Midwest Industries Combat Rail 15" M-LOK | +7.5" past | +6.0" past | +4.7" past | +3.5" past | Fits | Fits | Fits | Fits | Fits |
| Aero Precision ATLAS S-ONE 15" M-LOK | +7.5" past | +6.0" past | +4.7" past | +3.5" past | Fits | Fits | Fits | Fits | Fits |
| Magpul MOE M-LOK Drop-In Handguard, Carbine | Wrong length | Wrong length | Fits | Fits | Fits | Wrong length | Wrong length | Wrong length | Wrong length |
| Magpul MOE Drop-In Handguard, Midlength | Wrong length | Wrong length | Wrong length | Wrong length | Wrong length | Fits | Wrong length | Wrong length | Wrong length |
| Magpul MOE M-LOK Drop-In Handguard, Rifle | Wrong length | Wrong length | Wrong length | Wrong length | Wrong length | Wrong length | Wrong length | Fits | Fits |
Gas Block and Handguard
What fits under each handguard.
Aero Precision Low Profile Gas Block .750
- Fits Palmetto State Armory 13.5" Lightweight M-LOK Rail · Midwest Industries Combat Rail 15" M-LOK · Bravo Company MCMR-13 M-LOK Rail · Midwest Industries Combat Rail 9.25" M-LOK · Aero Precision ATLAS S-ONE 9.2" M-LOK · Bravo Company MCMR-10 M-LOK Rail · Geissele MK16 Super Modular Rail 13.5" M-LOK · Aero Precision ATLAS S-ONE 15" M-LOK · Midwest Industries Combat Rail 7" M-LOK
- Won't fit Magpul MOE Drop-In Handguard, Midlength · Magpul MOE M-LOK Drop-In Handguard, Carbine · Magpul MOE M-LOK Drop-In Handguard, Rifle Drop-in handguards are held by the front sight base cap. Pair it with an A2 front sight base.
Superlative Arms Adjustable Bleed-Off Gas Block .750
- Fits Palmetto State Armory 13.5" Lightweight M-LOK Rail · Midwest Industries Combat Rail 15" M-LOK · Bravo Company MCMR-13 M-LOK Rail · Midwest Industries Combat Rail 9.25" M-LOK · Aero Precision ATLAS S-ONE 9.2" M-LOK · Bravo Company MCMR-10 M-LOK Rail · Geissele MK16 Super Modular Rail 13.5" M-LOK · Aero Precision ATLAS S-ONE 15" M-LOK · Midwest Industries Combat Rail 7" M-LOK
- Won't fit Magpul MOE Drop-In Handguard, Midlength · Magpul MOE M-LOK Drop-In Handguard, Carbine · Magpul MOE M-LOK Drop-In Handguard, Rifle Drop-in handguards are held by the front sight base cap. Pair it with an A2 front sight base.
Aero Precision Low Profile Gas Block .625
- Fits Palmetto State Armory 13.5" Lightweight M-LOK Rail · Midwest Industries Combat Rail 15" M-LOK · Bravo Company MCMR-13 M-LOK Rail · Midwest Industries Combat Rail 9.25" M-LOK · Aero Precision ATLAS S-ONE 9.2" M-LOK · Bravo Company MCMR-10 M-LOK Rail · Geissele MK16 Super Modular Rail 13.5" M-LOK · Aero Precision ATLAS S-ONE 15" M-LOK · Midwest Industries Combat Rail 7" M-LOK
- Won't fit Magpul MOE Drop-In Handguard, Midlength · Magpul MOE M-LOK Drop-In Handguard, Carbine · Magpul MOE M-LOK Drop-In Handguard, Rifle Drop-in handguards are held by the front sight base cap. Pair it with an A2 front sight base.
Palmetto State Armory A2 Front Sight Base .750, F-Marked
- Fits Magpul MOE Drop-In Handguard, Midlength · Magpul MOE M-LOK Drop-In Handguard, Carbine · Magpul MOE M-LOK Drop-In Handguard, Rifle
- Won't fit Palmetto State Armory 13.5" Lightweight M-LOK Rail · Midwest Industries Combat Rail 15" M-LOK · Bravo Company MCMR-13 M-LOK Rail · Midwest Industries Combat Rail 9.25" M-LOK · Aero Precision ATLAS S-ONE 9.2" M-LOK · Bravo Company MCMR-10 M-LOK Rail · Geissele MK16 Super Modular Rail 13.5" M-LOK · Aero Precision ATLAS S-ONE 15" M-LOK · Midwest Industries Combat Rail 7" M-LOK An A2 front sight base will not fit under a free-float handguard. Use a low-profile gas block.
SLR Rifleworks Sentry 7 Adjustable Gas Block .750
- Fits Palmetto State Armory 13.5" Lightweight M-LOK Rail · Midwest Industries Combat Rail 15" M-LOK · Bravo Company MCMR-13 M-LOK Rail · Midwest Industries Combat Rail 9.25" M-LOK · Aero Precision ATLAS S-ONE 9.2" M-LOK · Bravo Company MCMR-10 M-LOK Rail · Geissele MK16 Super Modular Rail 13.5" M-LOK · Aero Precision ATLAS S-ONE 15" M-LOK · Midwest Industries Combat Rail 7" M-LOK
- Won't fit Magpul MOE Drop-In Handguard, Midlength · Magpul MOE M-LOK Drop-In Handguard, Carbine · Magpul MOE M-LOK Drop-In Handguard, Rifle Drop-in handguards are held by the front sight base cap. Pair it with an A2 front sight base.
Superlative Arms Adjustable Bleed-Off Gas Block .625
- Fits Palmetto State Armory 13.5" Lightweight M-LOK Rail · Midwest Industries Combat Rail 15" M-LOK · Bravo Company MCMR-13 M-LOK Rail · Midwest Industries Combat Rail 9.25" M-LOK · Aero Precision ATLAS S-ONE 9.2" M-LOK · Bravo Company MCMR-10 M-LOK Rail · Geissele MK16 Super Modular Rail 13.5" M-LOK · Aero Precision ATLAS S-ONE 15" M-LOK · Midwest Industries Combat Rail 7" M-LOK
- Won't fit Magpul MOE Drop-In Handguard, Midlength · Magpul MOE M-LOK Drop-In Handguard, Carbine · Magpul MOE M-LOK Drop-In Handguard, Rifle Drop-in handguards are held by the front sight base cap. Pair it with an A2 front sight base.
Parts Worth a Look
Our picks from the AR-15 catalog, with the lowest price we list (prices last checked Oct 4, 2026).
Handguard
Budget Pick
Palmetto State Armory 13.5" Lightweight M-LOK Rail
13.5" · Free float · M-LOK
Free-float on a budget, with the barrel nut included.
$49.99 at Palmetto State Armory (sample price)
Best Value
Midwest Industries Combat Rail 15" M-LOK
15" · Free float · M-LOK
Full-length rail with anti-rotation tabs and good QD placement.
$149.99 at Primary Arms (sample price)
Premium Pick
Bravo Company MCMR-13 M-LOK Rail
13" · Free float · M-LOK · Proprietary nut
Lightweight, stiff, and the reference rail for midlength builds.
$224.95 at Brownells (sample price)
Start from a Complete Build
Every part already checked to fit. Open one in the builder and swap anything you like.
Sources
Updated Oct 5, 2026.