223 Remington vs 5.56×45: Throat, Jump, and Bullet Design (Not “Hotter Loads”)

Same bullet at the same muzzle velocity → the same flight path. What really separates 223 Remington from 5.56×45 isn’t a magic headstamp or a universally “hotter” recipe—it’s the chamber throat (freebore + leade) and how that geometry interacts with bullet ogive and seating depth. Get that right and pressure is predictable, accuracy is repeatable, and your dope lines up regardless of the label on the box.

External Ballistics: Headstamp Doesn’t Change Gravity

Trajectory and wind are driven by muzzle velocity, bullet shape/BC, and atmospherics. Match bullet and velocity and a 223 load and a 5.56 load will print essentially the same holds. “Different downrange” usually means “different velocity,” not a different name.

Internal Ballistics: Why Throat & Jump Matter

The throat starts with a short cylindrical freebore, followed by the leade into the rifling. A typical 223 throat is shorter/tighter; a typical 5.56 throat is longer/looser. With long-ogive 62–77 grain bullets at magazine length, a short/tight 223 throat can reduce jump enough that the bullet touches the lands early—raising start pressure in that specific chamber. That interaction (throat + ogive + seating depth + powder) is the mechanism that matters.

Where 223 Wylde Fits (the practical middle)

The 223 Wylde chamber was cut to keep match-friendly geometry while adding a little more room in front of the case mouth so longer noses don’t engrave too soon at mag-length COALs. In practice it lets you run both 223 and 5.56 ammunition with predictable jump and strong accuracy on common match bullets—without giving up reliability.

Historical Context (why the throats diverged)

Early AR-15/M16 development revolved around ~55-grain ball (M193). NATO later standardized 5.56 with heavier/longer ogive projectiles and tracers, which pushed military specs toward a longer, shallower leade to maintain reliability across lots and environments. That history explains today’s split: a typical 223 throat is shorter/tighter; 5.56 is longer/looser; 223 Wylde sits between to preserve accuracy with 223-style bullets while giving 62–77-grain bullets room to jump.

Reality Check on “Pressure”

Changing the rollmark doesn’t magically strengthen your steel. It’s the same barrel material and bore. What changes is how soon the bullet engraves and how the pressure curve starts. Separate from that, 223 and 5.56 are tested under different pressure methods (commercial SAAMI vs. NATO case-mouth EPVAT), which confuses comparisons. Bottom line: safe pressure is a product of your chamber/throat, bullet ogive and seating, and the powder you chose—not the headstamp alone.

Mini-14 Labeling (what the markings actually mean)

Most Mini-14 rifles are designed to use both 223 and 5.56 ammunition even when the barrel is marked “223.” The consistent exception Ruger calls out is the Mini-14 Target, which is 223-only. Always verify by your specific model and manual.

Setups That Behave (especially with 62+ grain bullets)

• Bullet choice: long, high-BC noses (OTM/HPBT) shine downrange but reduce jump in short/thin throats.
• Seating depth: track CBTO (base-to-ogive) with a comparator; that’s what controls jump. COAL alone can lie.
• Powder/loading: work up in your chamber; chase a consistent velocity node and watch brass condition as you adjust seating.
• Chamber selection: if you’ll run 62–77 grain profiles at mag length, 223 Wylde or 5.56 chambers give more jump margin. A true 223 chamber can be superb with lighter bullets or carefully tuned heavies.

Quick Throat Geometry Snapshot

Typical reamer prints show trends like these (numbers vary by maker): 223 uses a small-diameter, short freebore with a steeper leade; 5.56 uses a larger-diameter, longer freebore with a gentle leade; 223 Wylde blends the two—small-diameter freebore, extended length, gentle angle. The result is reliable room for longer noses while keeping a “match” feel at the ogive.

Match Shooter’s Corner: 223 Wylde with 80-Grain Bullets

In Service Rifle and other match formats, shooters often run 77-grain magazine-length loads for rapid stages and step up to 80-grain bullets for 600-yard slow-fire. Here’s how that plays with 223 Wylde:

• Twist: 1:8 or faster is the standard for 80s; many top barrels are 1:7–1:7.7.
• Overall length: 80-grain OTM/HPBT bullets are long. Typical OALs around 2.43–2.50″ exceed AR-15 magazine length, so these are single-loaded for slow-fire. Use CBTO to hold a consistent jump.
• Seating & jump: start with a known safe CBTO (find first contact, then back off). Many tangent/hybrid 80s shoot with ~0.010–0.040″ jump; confirm what your barrel wants.
• Velocity envelope: from 20–24″ match barrels, 80-grain loads commonly run in the mid-2600s to low-2700s fps when tuned (temperature and lot dependent). Chronograph and true.
• Why Wylde helps: its longer, gentle leade gives heavy ogives room to enter the rifling smoothly, which keeps start pressure predictable while preserving the accuracy feel of a “tight” freebore.

Stage Strategy (quick hits)

• 200/300-yard rapids: 75–77-grain mag-length loads keep feed reliable and wind manageable.
• 600-yard slow-fire: single-load 80s for a little more BC and a calmer vertical. Confirm your waterline at distance, not just on paper at 100.
• Log CBTO & velocity by lot: long 80s are sensitive to small seating changes; record everything.

Common 5.56×45 Cartridges (quick reference)

• M193 / XM193 — 55-grain FMJ ball.
• M855 / SS109 / XM855 — 62-grain “green tip” with steel penetrator.
• M856 — 64-grain tracer.
• Mk262 Mod 0/1 — 77-grain OTM long-range load.

Note: nose shapes vary; longer ogives reduce jump in short throats and can raise start pressure if seated to mag length in a tight 223 chamber.

Field Process (do this and stop guessing)

1. Pick the bullet for the job (55s inside ~300; 69–77s for reach; 80s for single-load slow-fire).
2. Chronograph your rifle and atmospherics—build dope from your real MV.
3. Measure CBTO/jump by bullet and log it; re-check with new lots and as the throat wears.
4. Confirm holds at 300/500/600 and true the solver to reality.

Myths vs. Reality

• “5.56 is longer.” Case exterior dimensions overlap; the meaningful difference is throat geometry, not case length.
• “5.56 is always hotter.” Test methods and chambers differ. Your rifle’s pressure comes from throat/jump/bullet/seating/powder—not the label.
• “223 and 5.56 have different trajectories.” Same bullet + same MV = same dope. Period.

Tags: 223 Remington; 5.56×45; 223 Wylde; throat; jump; ogive; CBTO; Service Rifle; 80-grain; AR-15