Optic Mounting &
Zero Reference
MOA vs MRAD, common zero distances, height-over-bore, ring height selection, torque specs, and cant/level basics. The practical information you need to mount an optic correctly and zero it with confidence.
1 MOA = 1.047" at 100 yards (commonly rounded to 1" at 100 yards). Most American scopes click in ¼ MOA increments = 0.25" per click at 100 yards. MOA is intuitive for shooters who think in inches and yards.
- 1 MOA ≈ 1" at 100 yd, 2" at 200 yd, 5" at 500 yd
- ¼ MOA click = 0.25" at 100 yd = the most common adjustment
- ½ MOA click = 0.5" at 100 yd (found on some hunting scopes)
- ⅛ MOA click = 0.125" at 100 yd (competition/precision scopes)
1 MRAD = 3.6" at 100 yards = 10 cm at 100 meters. Most MRAD scopes click in 0.1 MRAD increments. The decimal math is simpler for range estimation and wind calls. Dominant in military, long-range competition (PRS/NRL), and international markets.
- 1 MRAD = 3.6" at 100 yd = 10 cm at 100 m
- 0.1 MRAD click = 0.36" at 100 yd = 1 cm at 100 m
- 10 clicks = 1 MRAD = clean decimal math at any distance
- Range estimation: (target size in meters ÷ size in mils) × 1000 = range in meters
Which should I choose? Either system works. Pick one and stay consistent — scope reticle and turret adjustment should match (MOA reticle + MOA turrets, or MRAD reticle + MRAD turrets). Mixing reticle and turret units (MOA reticle + MRAD turrets) creates unnecessary math in the field. For most American hunters and recreational shooters, MOA is fine. For PRS/NRL competition or military-style use, MRAD is the standard.
| Zero Distance | Best For | Caliber Context | Practical Notes |
|---|---|---|---|
| 25 yards | Pistol red dots, close-range confirmation | All pistol calibers | Quick zero confirmation; not a precision zero for rifles. Coincides with ~100-yd zero for 5.56 with ~2.5" height-over-bore |
| 36 yards | AR-15 / 5.56 "battle zero" | 5.56 NATO / .223 Rem | The 36/300 zero: zeroed at 36 yd, the bullet returns to line of sight at ~300 yd. Maximum point-blank range concept. Never more than ~5" high or low from 0–350 yd |
| 50 yards | 5.56 CQB zero, .300 BLK, rimfire | 5.56, .300 BLK, .22 LR | Popular for SBRs and suppressed builds. For .300 BLK subsonic, 50 yd is often the max practical zero distance |
| 100 yards | Standard rifle zero | .308 Win, 6.5 Creedmoor, .223, most rifles | The most common rifle zero distance. Establishes a clean baseline for drop calculations at longer ranges |
| 200 yards | Precision bolt rifle, hunting | .308 Win, 6.5 CM, magnums | Reduces holdover at common hunting/engagement distances. Bullet impact is ~2" high at 100 yd for most .30-cal loads |
| MPBR (Max Point-Blank Range) | Hunting — varies by caliber | Any | Zero set so the bullet stays within a defined kill zone (usually ±3") over the maximum practical distance. Calculator-dependent. |
The optic sits above the bore centerline. This offset means the bullet path and the line of sight are two separate lines that only intersect at the zero distance(s). At close range (inside the near zero), the bullet impacts BELOW the point of aim — often by the full height-over-bore measurement.
| Mount Type | Typical Height-Over-Bore | Context |
|---|---|---|
| AR-15 flat-top + low mount red dot | ~2.5" | Standard AR height; absolute or lower 1/3 cowitness |
| AR-15 + LPVO in 1.54" mount | ~2.8" | Common LPVO setup; Badger, Scalarworks, Geissele mounts |
| AR-15 + 1.93" high mount | ~3.2" | Heads-up / passive aiming; Unity FAST, Scalarworks 1.93 |
| Bolt rifle + low rings | ~1.5–1.8" | Typical hunting/precision bolt rifle setup |
| Bolt rifle + 20 MOA rail + medium rings | ~1.8–2.1" | Long-range precision; extra elevation travel for distance |
| Pistol + slide-mounted red dot | ~1.0–1.2" | Minimal offset; direct slide mount (MOS, optic-ready slide) |
Close-range offset: With a 2.5" height-over-bore and a 100-yd zero, the bullet impacts approximately 2.5" below your point of aim at 3–10 yards. For home defense and CQB, this means you must aim higher at close range to hit where you intend. This is the most commonly overlooked zeroing concept.
Ring height determines how high the scope sits above the rail or receiver. The objective bell (front lens housing) must clear the barrel, handguard, or any accessory. Too low = contact and damage. Too high = uncomfortable cheek weld and excessive height-over-bore.
| Objective Lens | Typical Ring Height Needed | Notes |
|---|---|---|
| 24mm (compact scope) | Low | Most low rings work; tight clearance on some handguards |
| 32–40mm (standard) | Low to Medium | Most common; verify clearance with barrel nut and handguard |
| 44mm (hunting scope) | Medium | May need medium rings depending on receiver height |
| 50mm+ (large objective) | Medium to High | Common on precision scopes; may require high rings or a 20 MOA rail |
| 56mm (large precision) | High | High rings or cantilevered mount; significant height-over-bore increase |
Over-torquing damages the scope tube, strips threads, or warps the ring. Under-torquing allows the scope to shift under recoil. Always use a quality torque wrench (FAT wrench, Wheeler, Fix It Sticks, Vortex Torque Wrench).
| Component | Typical Torque | Notes |
|---|---|---|
| Ring cap screws (scope rings) | 15–18 in-lb | Most manufacturers specify 15–18; NEVER exceed 25 in-lb on scope ring screws |
| Ring base / mount to rail screws | 25–35 in-lb | Varies by mount manufacturer; check specific documentation |
| Picatinny rail to receiver screws | 25–35 in-lb | Nightforce recommends 25 in-lb; others may differ; use thread locker |
| Red dot mount screws | 15–25 in-lb | Varies widely; Aimpoint, Trijicon, and Holosun each have specific specs |
| LPVO cantilever mount | 25–35 in-lb (base), 15–18 in-lb (ring caps) | Base bolts and ring cap screws have DIFFERENT torque specs |
| Pistol red dot screws | 10–15 in-lb | Small screws; easy to strip; use correct bit and thread locker |
Thread locker: Use medium-strength (blue/purple) thread locker on all optic mount screws unless the manufacturer says otherwise. Loctite 242/243 or Vibra-Tite VC3 are standard. Never use red (permanent) thread locker on optic screws.
If the scope reticle is not perfectly level with the rifle, your windage and elevation adjustments will not track accurately at distance. Even 1–2° of cant creates meaningful lateral shift at 500+ yards. Use a scope leveling kit during installation. A bubble level (Wheeler, Vortex, Badger Ordnance) mounted on the scope or rail confirms level in the field.
A 20 MOA (or 20 MRAD) canted rail tilts the scope slightly downward at the muzzle end. This gives the scope more elevation adjustment range for long-range shooting — the turret starts closer to the bottom of its travel, leaving more room to dial up. Standard on most precision bolt rifles shooting beyond 600 yards. Not needed for close to mid-range use.
