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The 5.56x45mm NATO is the military version of the .223 Remington, which is one of the most widely used centerfire cartridges today. Starline’s 5.56x45mm brass is identical to Starline’s .223 Remington brass except for a slight change in the metallurgy making it harder at the base of the case.

When loaded at .223 Remington pressures, Starline's .223 brass is safe to use in any firearm chambered for .223 or 5.56x45mm. If loaded to 5.56 pressures, you need to use firearms labeled for use with 5.56mm. It can be unsafe to fire 5.56mm ammunition in firearms with a .223 Remington chamber.

If out of stock check out our .223 Remington cases.

**WARNING** In firearms that use a floating firing pin (such as the AR-15 and its variants), dropping the bolt on a chambered round could lead to a slam fire. It is important that these firearms are loaded from the magazine so that the bolt loses inertia when it strips a round from the magazine. It is also important NOT to use sensitive primers that aren’t designed for use in an AR, as this increases the chance of a slam fire.



* Starline Brass does not sell any loaded ammunition. What you are purchasing are brass cases only and will need to be loaded into ammunition in order to be fired from a firearm.



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Robert Posvic
Goldsboro, NC
November 27, 2022
Product Review
Great brass. Weight is now similar to LC 5.56 brass. At one time Starline 5.56 brass was much heavier (7-8 grains on average). A load worked up in LC 5.56 brass will now work with 5.56 Starline with minimal changes. But still work up from below just to be sure.

J. Norton
Cedar Bluff, AL
March 06, 2022
Product Review
Another great product from Starline!

Christopher Kelley
Carlsbad, ca, CA
July 29, 2021
Product Review
Tried them all. Simply the best!!! Enough said.

Joe Leighty
Scottdale, PA
November 26, 2020
Product Review
I have used Starline brass for years in many calibers but just received my first 5.56x45 brass a few weeks ago. I finally got around to working with it and I can say without a doubt it is some of the best 5.56x45 or 223 brass that I have worked with. I am chamfering the inside and outside of the case mouth and neck sizing to assure proper neck tension but other than that I am not doing anything else. The case length is well within acceptable tolerance of a few thousandths, the primer pockets are clean and tight, the necks and bodies are in great shape, even though they are shipped in a plastic bag with 1,000 cases, and they are all bright, shiny and flaw free. After loading some they function perfectly and will last a very long time. I've ordered two batches of these cases so absolutely I would recommend them to my friends and anyone else interested in loading this caliber.

William Dellisanti
Okeechobee, Florida
October 18, 2018
Product Review
Last year Star-line sent me a sample of the new 223 REM brass. The brass was excellent. Primer pockets were uniform. OAL was excellent so there was no work involved in the primer pocket or trim length. The brass was within spec and could be loaded out of the box. Of course that is never recommended. Fully size all new brass for a semi or auto loading rifles or pistols. I expressed my concerns over the lack of a 5.56 NATO stamp, as probably others did also. Star-Line has responded. No longer will I need to mix and match head stamps. I now can count on using one and only one brass for my AR's. Availability of a high quality brass at a cost effective price no longer a issue. In many ways this brass rivaled Lapua at 1/3 the cost. Thank You Star-Line. Will