It sounds a lot like the 223 or the 222 Mg. as far as case capacity is concerned dooesn't it?

I have always thought that the only thing wrong with the 223 is that short neck, so I took a .255" reamer and lengthened the neck in a Savage model 12 rifle that I have, to the point that I can simply run 222 Mg. brass through the 223 die and load it according to 223 data. The 223 is throated long enough so that no rethroating was necessary--or even desireable.

What I have is a 223 with a neck long enough that the overall length of the brass is 1.850 an increase of about .100 over the 223.

I chronographed it thourally before and after making the alteration, and noted no change in average velocity regardless of the brass used. I did note, however, a decrease in the shot to shot variation in velocity, which was only 1/2 what it is when the regular 223 brass is used, and the groups went from about 1" to about 3/4".

I am completely satisfied with this alteration, it doesn't change anything other than the length of the neck, regular 223 brass can still be used, and it appears to have enhanced the accuracy.

One thing to watch though. I do not own a 222 Mg. but if I did, I would be sure to keep this stuff seperate from 222 Mg. ammo because it looks almost exactly the same. One of these in a 222 Mg. would almost surely result in case failure which is very bad news indeed.