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Ruger AR-556

• easy
• Shop tier 2
• high confidence
• Rifle
• direct impingement
• modular
• toolless field strip
• budget ar

field strip ~2 min · reassembly ~3 min · detail strip ~25 min

Specifications

Model-specific safety

• The bolt cam pin MUST be installed. Without it the bolt cannot lock into the barrel extension, and firing in that condition can destroy the rifle and seriously injure the shooter. The firing pin retaining pin will not install without the cam pin in place — that is a designed safeguard, so if the retaining pin will not go in, stop and find out why.
• The safety selector only engages when the hammer is cocked. If it will not rotate to SAFE, the hammer is down.
• The buffer and buffer spring are under compression. When you depress the buffer retainer, control the buffer.
• Gas system components are extremely hot immediately after firing.
• The upper receiver swings forward as soon as the rear takedown pin is disengaged. Ruger warns this can pinch fingers wrapped around the magazine well.

Under spring tension

• Buffer and buffer spring in the receiver extension
• Extractor spring
• Magazine springs

Easily lost parts

Bolt cam pin · Firing pin retaining pin · Extractor pin · Buffer retainer and spring

Tools

No tools required for the field strip.

Shop difficulty

Shop tier 2 Tier 2 — moderate among rifles and carbines, for the full job: strip to the parts that get coated and put it back together working. 72 parts, the standard AR-15 full strip. It needs several captive detents and plungers (takedown and pivot detents, buffer retainer, selector detent, bolt catch plunger), roll pins, and a hammer spring that only works one way round. These are common traps with common jigs, and nothing is timed.

Parts: 72 numbered parts (Complete rifle, standard handguard (72 line items; free-float supplement excluded)), from Ruger AR-556 Owner’s Manual — Sturm, Ruger & Co., Inc., p. 44–45 ruger-docs.s3.amazonaws.com [2].

Bench time: about 45 min to strip, 70 min to rebuild (estimate). Full AR strip: BCG, upper furniture and gas system, lower FCG, buffer, bolt catch, pivot/takedown detents. Rebuild time is driven by the detents and the roll pins.

Small parts: 13 pins, 12 springs, 8 detents or plungers (counted from the manufacturer's parts list (one per key number unless a quantity is given))

What comes off for coating

• Upper: handguard / delta ring or rail, gas block and gas tube, front sight (if fitted), flash hider, forward assist, ejection port cover and pin — armorer's wrench
• Bolt carrier group: firing pin retaining pin, firing pin, cam pin, bolt, extractor pin, extractor, spring, ejector roll pin, ejector, spring
• Lower: buffer, buffer spring, buffer retainer and spring, castle nut / stock, pistol grip (selector detent and spring), selector, hammer, trigger, disconnector and springs, bolt catch roll pin, bolt catch, plunger, spring, magazine catch, trigger guard roll pin, front pivot pin and detent, rear takedown pin and detent — roll pin punches, vise block

Special tools

• AR armorer's wrench — Castle nut, barrel/muzzle
• upper and lower vise blocks — Holding receivers
• roll pin punches and starters (1/8, 3/32, 5/64 in) — Bolt catch, trigger guard, gas block roll pins
• pivot pin detent tool — Front pivot pin detent
• slave pin — Trigger/hammer reassembly

Known pain points

• The front pivot-pin detent and spring go in sideways under compression and launch across the room without a pivot-pin tool. (reassembly)
  Source: DIY AR-15 Build: Pivot Pin Installation — ITS Tactical itstactical.com [3] — “When inserting the detent that holds in the Pivot Pin, it’s quite common for it to turn into a Pegasus Missile and shoot across the room along with the spring that’s under tension.”
• A hammer spring fitted backwards can look right but will not detent the trigger pin. The result is light strikes and the pin walking out. (reassembly)
  Source: (Gunsmithing the AR-15 #2) The 30-Second AR Check — Gun Tests gun-tests.com [4] — “A hammer spring installed backwards will give a light primer strike causing misfires, and although it may appear to be laying on and detenting the trigger pin, it in fact will not.”

See also 4 documented reassembly problems and their fixes.

Fit or check on rebuild

• Hammer spring orientation and pins flush — A reversed spring will not detent the trigger pin.
  Source: (Gunsmithing the AR-15 #2) The 30-Second AR Check — Gun Tests gun-tests.com [4] — “Hammer spring is correctly installed with both legs horizontal, spread out against inside wall of receiver, and laying on top of trigger in properly in the at pin’s outboard groove, acting as a detent for same.”
• Gas block alignment with port — A misaligned gas block short-strokes. Standard check.
• Function check (safety, trigger reset, feeding, extraction) — Standard after any detail strip. No single source.
• Re-zero sights or scope — Sights and optics come off for coating, and point of impact must be re-confirmed. This is a standard check, so no source.

This is Pew-Takedown's rating, not the manufacturer's. How tiers are rated. Forum reports are owners' experience, not specifications.

Manufacturer videos

Official videos from Sturm, Ruger & Co.'s own channels, linked rather than copied. Where a video and the steps on this page differ, follow the manufacturer's manual and video.

• Ruger® AR-556® Disassembly Tech Tip RugerFirearms field strip · 2015-06-10
• Ruger® AR-556® Reassembly Tech Tip RugerFirearms reassembly · 2015-06-10
• Ruger® AR-556® Cleaning Tech Tip RugerFirearms cleaning · 2015-06-09
• Ruger® AR-556® Delta Ring Tech Tip RugerFirearms detail strip · 2015-06-09
• Ruger® AR-556® MPR 450 Bushmaster Proper Magazine Alignment Tech Tip RugerFirearms operation · 2021-11-22
  Covers: Ruger AR-556 MPR in .450 Bushmaster (per description)

Procedures

Diagrams

public domain

These are reproduced from government technical manuals, which are not subject to copyright. Manufacturer manual diagrams are not reproduced here — the entry links to the manual instead.

Torque specifications

No sourced torque values from the manufacturer are recorded for this firearm. Where a fastener has a specified torque — action screws, scope bases, muzzle devices, barrel nuts — get it from the manufacturer or a gunsmith rather than estimating it.

What the manufacturer does say: The manufacturer's documents give no torque value. They say: "Tighten the Delta Ring by turning it counterclockwise with your thumb and index finger (two-finger tight)." (Ruger AR-556 Owner’s Manual, PDF p. 37) "CAUTION: Do not over tighten the Delta Ring. Use two fingers only to tighten." (Ruger AR-556 Owner’s Manual, PDF p. 37)

Parts list

Transcribed from the manufacturer's parts list (Ruger AR-556 Owner’s Manual — Sturm, Ruger & Co., Inc., p. 44–45 ruger-docs.s3.amazonaws.com [2]) — AR-556 (standard handguard); the manual's free-float handguard supplemental list is not included. Exploded views on pp. 46, 47 & 48. Key numbers refer to the exploded view in that document.

Function check

• Verify the rifle is unloaded with no magazine inserted before each step.
• Charge the rifle to cock the hammer, place the selector on SAFE, and press the trigger. The hammer must not fall.
• Move the selector to SEMI and press the trigger. The hammer should fall.
• Hold the trigger to the rear, charge the rifle, then release the trigger slowly and listen for the disconnector to release the hammer to the trigger.
• Press the trigger again. The hammer should fall.
• Insert an empty magazine, charge the rifle, and confirm the bolt locks back.

Maintenance

Lubrication points

• Bolt locking lugs and body
• Cam pin and its track
• Outside of the carrier
• Gas rings
• Charging handle rails

Cleaning notes

A direct-impingement AR runs better wet than dry. Carbon on the bolt tail is normal and does not all need removing — focus on the locking lugs, gas rings, chamber, and bore. Do not scrape the bolt tail with steel.

Suggested inspection interval: roughly every 1000 rounds. This is a general guideline, not a manufacturer specification.

Wear parts to inspect

Gas rings · Extractor and its spring insert · Bolt (check the cam pin hole and lugs for cracks) · Buffer spring · Gas key staking

Common issues

Similar manual of arms

• AR-15 (M16/M4 Pattern)

Legal notes

Sourcing