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223 vs 556

4700 Views 8 Replies 8 Participants Last post by  Beltfire
Starting to reload again.I've reloaded shells several times with out checking case length and never had a problem in my AR.Bought some once fired miltary brass and started checking case length.The cases varied quite abit.Took the longest case,resized it and dropped it in the barrel.It seated all the way in.Doe,s the military have a different case length than commertial,or is a 556 chamber different than 223?
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Winchester ammunition statement on .223 vs 5.56

This is off of a Winchester Ammunition Press Release For LE - says pretty much the same thing as pdembek says....just verifys it.


The cartridge casings for both calibers have basically the same length and exterior dimensions.

The 5.56 round, loaded to Military Specification, typically has higher velocity and chamber pressure than the .223 Rem.

The 5.56 cartridge case may have thicker walls, and a thicker head, for extra strength. This better contains the higher chamber pressure. However, a thicker case reduces powder capacity, which is of concern to the reloader.

The 5.56mm and .223 Rem chambers are nearly identical. The difference is in the "Leade". Leade is defined as the portion of the barrel directly in front of the chamber where the rifling has been conically removed to allow room for the seated bullet. It is also more commonly known as the throat. Leade in a .223 Rem chamber is usually .085". In a 5.56mm chamber the leade is typically .162", or almost twice as much as in the 223 Rem chamber.

You can fire .223 Rem cartridges in 5.56mm chambers with this longer leade, but you will generally have a slight loss in accuracy and velocity over firing the .223 round in the chamber with the shorter leade it was designed for.

Problems may occur when firing the higher-pressure 5.56mm cartridge in a .223 chamber with its much shorter leade. It is generally known that shortening the leade can dramatically increase chamber pressure. In some cases, this higher pressure could result in primer pocket gas leaks, blown cartridge case heads and gun functioning issues.

The 5.56mm military cartridge fired in a .223 Rem chamber is considered by SAAMI (Small Arm and Ammunition Manufacturers Institute) to be an unsafe ammunition combination.
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