Why Is My AR-15 Build Not Accurate? Common Accuracy Problems After Assembly
The most common accuracy problems on new AR-15 builds are an improperly torqued barrel nut (causing barrel movement), a non-free-floated handguard putting pressure on the barrel, loose scope or optic mounting, a crown damaged during assembly, and using the wrong ammunition for your twist rate. Most accuracy issues are assembly-related, not parts quality issues.
Why It Matters
A properly built AR-15 with quality components should shoot 1 to 2 MOA (1 to 2 inches at 100 yards) or better. If your new build is shooting 3 to 5 MOA or worse, something in the assembly is likely wrong. Identifying and fixing assembly issues is far more productive than buying better barrels or ammunition — the rifle cannot outshoot its assembly quality.
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Common accuracy problems and solutions (in order of likelihood):
1. Barrel nut torque:
- The barrel nut must be torqued to specification (30 to 80 foot-pounds for mil-spec, or per manufacturer instructions for proprietary nuts)
- Under-torqued: Barrel can shift under recoil, causing wandering zero
- Over-torqued: Can stress the barrel extension and receiver threads
- Use a proper torque wrench, not a breaker bar
- Apply aeroshell grease to receiver threads before installation
2. Handguard-barrel contact:
- If using a drop-in handguard, the front sight base and handguard contact the barrel, which is normal but limits accuracy potential
- Free-float handguards should not touch the barrel at any point
- Check by sliding a dollar bill between the barrel and handguard — it should pass freely with no contact
- If the handguard is touching, the barrel nut or handguard installation needs adjustment
3. Optic mounting:
- Scope rings must be torqued to specification (usually 15 to 25 inch-pounds)
- Red dot mounts: torque to manufacturer spec
- Use a proper scope mounting procedure: level the rifle, level the reticle, tighten in an alternating cross pattern
- Loose optic mounts are the number one cause of wandering zero
- Ensure the scope base or mount is on the upper receiver, not bridging the handguard-to-receiver junction
4. Crown damage:
- The barrel crown (the very end of the muzzle) must be perfectly concentric
- Damage from dropping, improper muzzle device installation, or cleaning rod contact degrades accuracy significantly
- Inspect the crown for nicks, burrs, or unevenness
- A damaged crown requires re-crowning by a gunsmith or barrel replacement
5. Ammunition and twist rate mismatch:
- A 1:7 twist barrel shoots heavy bullets (69 to 77 grains) best
- A 1:9 twist barrel prefers lighter bullets (55 to 62 grains)
- Shooting 55-grain ammunition through a 1:7 twist barrel may produce poor accuracy
- Try several ammunition brands and weights to find what your barrel prefers
6. Bolt and barrel headspace:
- Out-of-spec headspace causes inconsistent ignition and accuracy issues
- Always check headspace with go and no-go gauges after assembling a new upper
- Excessive headspace is a safety hazard, not just an accuracy issue
Build Impact
Before spending money on a new barrel, work through this checklist. Ensure your barrel nut is properly torqued, your handguard is truly free-floated, your optic is mounted and torqued correctly, and you are shooting ammunition suited to your twist rate. Then shoot from a stable rest (bags or bipod) to eliminate shooter error. Most new-build accuracy issues disappear after correcting one or two assembly problems.