[Jeff Higgins]

You guys need to understand that external dimensions of the 5.56 NATO and .223 Remington cases are identical. The only difference (other than the crimped in primers) is in the thickness of the brass, with the NATO stuff being thicker. Since that added thickness is not added to the outside, it has to be on the inside, thereby reducing capacity.

The added capacity of the .223 does not afford it increased velocity over the 5.56. All it means is that it takes more powder in that larger case to reach the same velocities as the smaller case. Reloading data is typically developed in, and written for, commercial .223 brass. Using that data in military 5.56 brass will result in dangerous pressures unless the charges are reduced to compensate for the reduced capacity. As far as the hobby hand loader is concerned, velocities with the two cases should be identical - it just takes less powder to achieve the same velocity with the smaller capacity 5.56 brass.

There is no such thing as setting dies to ".223 specs". Like I said, .223 and 5.56 brass is externally identical. The only possible difference is in bullet seating depth, which we will typically tailor to the specific chamber in the specific gun for which we are loading. The brass makes no difference; it's the rifle's chamber that determines this dimension. In other words, for a given bullet in a given rifle, we will use the same seating depth regardless of which brass we are using.

For you semi-auto fans, sometimes chamber length will not be the determining factor in cartridge overall length. That damn magazine will be what limits this dimension. If you seat bullets out to match the rifle's chamber, striving for the typical .010" off the leade, the rounds probably won't fit in the magazine. They will be too long. Us bolt action/single shot guys don't have to deal with that...

Anyway, that's a long-winded way of saying the only real consideration for reloading the two different cases is the powder charge. It must be reduced in the 5.56 brass to keep pressures safely under SAAMI maximums. If you have a chronograph (every hand loader should...) it is an easy matter to match velocities between your 5.56 and .223 brass. At that point they become functionally equivilent. Just keep them separate, keep track of how many firings are on each lot, and keep them properly trimmed. You will find the thicker military stuff will outlive the commercial stuff by a significant number of firings.