The Complete 5.56 and .223 Buyer’s Guide for AR Owners

Old Army is a veteran owned small business in Spokane Valley, Washington. This guide gives plain language answers on 5.56, .223, and M193 so you can buy with confidence and shoot safely. If you want to see what is currently available, start with our ammunition category or the product detail for Old Army Ammunition OA-556X45-B-55G. For bulk or fit questions, contact our team.

Quick Take, 5.56 vs .223 at A Glance

Same caliber, different standards

.223 Remington is a commercial cartridge standardized by SAAMI, and 5.56×45 NATO is a military family of cartridges tested to NATO methods. Chambers and pressure test methods differ, which is why interchange is not one to one. The SAAMI FAQ explains where use is generally accepted and where caution is advised.

Very short summary

If your barrel is marked 5.56, you can typically use either .223 or 5.56 from reputable manufacturers. If your barrel is marked .223 only, prefer .223 loads and do not assume every 5.56 lot will be safe in that chamber. The 2025 SAAMI rifle standard sets the current reference for pressure and velocity test methods used by commercial makers.

Where M193 fits

M193 is a classic 55 grain ball load in the 5.56 family. It often mirrors the bullet weight of common .223 55 grain FMJ, but it is built and validated against different military test procedures. When in stock, our OA-556X45-B-55G is positioned for training and range use.

What M193 Means

M193 is a 55 grain full metal jacket ball round associated with early AR platforms. It was designed around longer barrels and traditional twist rates. The key point is standards, commercial .223 and military 5.56 use different pressure measurement methods and test barrels. That difference is why interchange with .223 chambers deserves care. If you want the current industry baseline, review the 2025 SAAMI Z299.4 document.

M193 quick facts

• Bullet weight, 55 grains, FMJ boat tail variants are common.
• Use cases, training, general range work, confirming zero at common distances.
• Barrel behavior, works well in 1-12 to 1-9 twist barrels, also fine in 1-7, though many rifles group heavier bullets better.
• Labeling reality, commercial boxes may say “M193” as a performance style, always check the barrel marking and follow the maker’s guidance.

If you want help matching loads to barrel twist or typical distance, reach out on the contact page.

M193 vs M855, Practical Differences

Both are 5.56 family ball loads, but they behave differently.

At a glance

• M193 uses a 55 grain lead core FMJ. It can shoot flat at shorter ranges from 16 to 20 inch barrels.
• M855 is 62 grain with a steel penetrator under the jacket. Expect a different point of impact and grouping in some barrels. Some ranges restrict steel penetrator projectiles, always confirm your range rules.

Legal clarity

Do not confuse M855 or other common 5.56 ball loads with the federal definition of armor piercing handgun ammunition. The term “armor piercing” in federal law covers specific projectile constructions intended for use in handguns. Review the ATF resource on armor piercing ammunition for the statutory definition.

Tip for mixed use rifles

If you switch between 55 and 62 grain loads, keep two simple zero confirmations in your range notebook, one for each load, and reconfirm seasonally.

.223 Rem vs 5.56 NATO Interchange

You will hear that .223 and 5.56 are the same. They are not the same standard even though cases look alike.

Test methods differ

SAAMI uses a conformal transducer in a SAAMI test barrel, while NATO methods use different instrumentation and proof protocols. Direct pressure number comparisons can mislead. The 2025 SAAMI rifle standard outlines the current commercial procedures.

Chamber geometry differs

Freebore diameter and throat length differ between typical .223 and 5.56 chambers, which affects pressure. SAAMI’s FAQ on interchangeability and the SAAMI interchangeability bulletin explain where alternate use is generally accepted and where it is not.

Practical guidance

• Barrel marked 5.56, you can usually run either .223 or 5.56 from mainstream manufacturers that follow standards.
• Barrel marked .223 only, stick to .223. Do not assume every 5.56 lot will be safe in that chamber.
• Hybrid chambers like .223 Wylde are engineered for flexibility, but still follow your barrel maker’s directions.
• When in doubt, ask your rifle manufacturer or a competent gunsmith, then test small sample lots and inspect for pressure signs.

Have a question about a specific AR barrel and a case of 5.56 you are considering, send us a note through Contact us.

How to Choose for Your AR

Use this quick checklist to match ammo to your intent, then confirm zero at the distance you care about.

Step 1, confirm your chamber

Read the barrel marking or your rifle manual. If you see 5.56 or .223 Wylde you have the most flexibility. If you see .223 Rem only, prefer .223 labeled loads that follow SAAMI norms.

Step 2, pick a bullet weight for the job

• 55 grain class, general drills, training, and many carbine matches under 200 yards. Often labeled M193 style.
• 62 grain class, try it if your rifle groups it better or to match common military zero data.
• Heavier than 62, consider later as you stretch distance and refine wind calls.

Step 3, test by lot

Buy two or three small boxes from different lots. Shoot simple 5 shot groups, watch for reliable cycling, ejection pattern, and point of impact. When you find a winner, record the lot code on your gear card.

Step 4, maintain safe habits

Keep .223 and 5.56 boxes separated in the range bag. Do not mix loose rounds from different lots in the same magazine. Reconfirm zero after any change in lot, bullet weight, barrel, or optic.

A straightforward way to set a baseline is to confirm function with a 55 grain load such as Old Army OA-556X45-B-55G, then note your group size and ejection pattern for comparison.

For Washington Readers

If you hunt in Washington, check current season pamphlets and equipment sections each year. Start with the state’s official hunting seasons and regulations, and review WAC 220-414 on firearms, ammunition, and equipment for restrictions like nontoxic shot requirements and unlawful methods.

Old Army serves shooters across the United States from Spokane Valley. For local pickup questions or regional regulations, reach us through Contact us.

Buying Online and How Ammunition Shipping Works

Buying 5.56 and .223 online is straightforward, but shipping has firm rules. For consumer orders in the United States, common carriers handle small arms ammunition as a limited quantity hazardous material that must travel by ground, in proper packaging, with the correct limited quantity diamond marking.

If you want the official checklist, UPS explains packaging, service level, and labeling on its page on how to ship ammunition. USPS does not accept ammo at all, and lists ammunition under domestically prohibited items in its shipping restrictions. For business shipping scenarios or special cases, also review USPS Publication 52, the Postal Explorer section on hazardous, restricted, and perishable mail.

What this means for you

• Expect ground delivery timelines and adult signature where required by carrier or local law.
• Do not try to mail ammunition through USPS. Use a carrier that accepts ammo and follow their rules.
• If you plan to ship ammo yourself, read the carrier instructions carefully and keep the limited quantity label handy.
• Have questions about an order from Old Army, reach us through Contact us and we will help you choose the right method.

State and range notes

• State and local rules change. Before a range trip or a move, check your local wildlife agency and range policies. Washington readers can start with the state’s hunting seasons and regulations and the WAC section on firearms, ammunition, and equipment.
• Always follow your range’s posted commands and safety procedures, even for routine practice.

Safe Storage and Shelf Life Basics

Modern, factory loaded centerfire ammunition is stable when stored correctly. The goal is to keep cartridges dry, cool, and clean, with minimal temperature swings. SAAMI maintains plain language guidance on safe handling that you can review in its advisories, including the section on recommendations for safe ammunition storage and handling.

Quick checklist

• Store in original boxes, inside a dry container with a desiccant pack.
• Avoid garages or attics with wide temperature swings.
• Keep ammo away from solvents, oils, and ultrasonic cleaners.
• Do not attempt to “wipe polish” cartridges with abrasive media.
• Discard any round with corrosion, dents, bullet setback, or pulled projectiles.
• Keep ammunition separate from firearms and from ignition sources.
• Follow your local regulations for transportation and storage.

Range Day Checklist and Etiquette

A little prep keeps training smooth and safe. The National Shooting Sports Foundation publishes practical safety material, including the basic rules of safe gun handling and range focused reminders on range safety and etiquette.

Pack list

• AR, magazines, sling, eye and ear protection, chamber flag.
• Targets, stapler or tape, sharpie, basic tools, lube, cleaning cloth.
• Two ammo types if testing, plus a notecard to log zero and lot codes.
• Trash bag to police brass and keep the bay tidy.

On the line

• Uncase with the muzzle pointed downrange, insert the chamber flag when not firing.
• Follow range officer commands without delay.
• Keep rifles benched and pointed safely during cold range periods.
• Confirm your zero with the exact load you intend to use next time.

If you need help picking a simple starter load for function checks, you can watch for stock updates on our ammunition page, then confirm grouping and ejection pattern before you buy in bulk.

How Old Army Gives Back

Old Army was founded by a retired Army Veteran in Spokane Valley. Part of every purchase helps support programs that strengthen service members and families through Army Family and Morale, Welfare and Recreation. If you want an official overview of what MWR provides, the MyArmyBenefits library has a current fact sheet on MWR programs and eligibility.

If your company is interested in co creating licensed products that align with our mission, you can learn more on our Licensing Opportunities page. For bulk ammo questions, custom bundles, or wholesale inquiries, use Contact us and we will route your note to the right person.

What to Do Next

• Confirm your chamber marking and pick a bullet weight for your purpose.
• Test a couple of lots, then record the winner’s lot code and your zero.
• Review carrier rules if you plan to ship ammo yourself, and never use USPS for ammunition.
• Save this guide, and share it with a new AR owner who could use a clean starting point.
• When you are ready to shop, begin with our ammunition page or the OA 55 grain listing, Old Army Ammunition OA-556X45-B-55G.
• Questions, custom requests, or local pickup by arrangement, send a note through Contact us.

FAQ

• Can I shoot 5.56 in a .223 marked barrel?
  Usually no, follow the barrel manufacturer’s guidance and SAAMI’s notes on interchange. If your barrel is marked .223 only, use .223 commercial loads.
• Is .223 Wylde safe for both .223 and 5.56?
  .223 Wylde chambers are designed for flexibility. Follow your barrel maker’s instructions and test small lots before buying in bulk.
• What twist rate works best for 55 grain M193 style loads?
  Many rifles group 55 grain bullets well in 1 in 9 or 1 in 12 twists, and most modern 1 in 7 barrels also shoot them acceptably. Let your groups decide.
• Will M855 damage steel targets?
  Many ranges restrict penetrator projectiles on steel targets. Check your range rules before you go and use appropriate backers.
• How long does factory ammo last in storage?
  Stored cool, dry, and clean, quality ammo can remain usable for many years. Inspect cartridges each season and rotate older training stock first.
• Does USPS ship ammunition?
  No. USPS lists ammunition as a domestically prohibited item. Use a carrier that accepts ammo and follow their rules.
• Can I order ammo to my home in Washington?
  In most cases yes for eligible buyers, but always check current state and local rules. If unsure, ask your local agency or your range.
• What zero distance should a new AR owner use?
  Common starting points are 50 or 100 yards. Pick one, confirm with your chosen load, and record the offset for other distances.
• Is steel cased .223 OK for training?
  It can be fine in many rifles. Test small quantities, watch for reliable cycling and extraction, and clean your chamber before switching back to brass cases.
• How do I ask Old Army about bulk or dealer pricing?
  Send a short note through Contact us and include your intended quantity and timeline. We will reply with options.