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.
The Practical Impact
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.