FC Headstamp

In any event, keep in mind maximum proof pressure for your rifle is 148% above the usually given maximum pressure, and your gun has to tolerate that without damage (though not a steady diet of it). Also, that maximum pressure isn't a maximum in the usual sense of being an absolute, not-to-exceed limit. What is given as a maximum pressure in manuals is a number SAAMI calls the Maximum Average Pressure (MAP). It is an average result for a ten round string. Individual rounds within the string can go higher. SAAMI limits that with a spec called Maximum Extreme Variation (MEV) and in a worst case, that would allow one round out of the ten to be 118% of the MAP value. The European CIP limits individual rounds to 115% of MAP. Further, SAAMI allows the average peak pressure for ten rounds to increase as the ammunition lot ages and the bullets get stuck harder into their brass. That allowance is given a different name, being called the Maximum Probable Lot Mean (MPLM), and it is 106% over MAP in the 223. So if the ammo isn't very old, it should be within the MPLM and be perfectly fine to fire without undue wear. Even if it went over a little, as long as you don't detect sticky case extraction, you should be good to go.
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I do not grant the same margin of forgiveness, a disciplined reloader should be able to see it coming long before 'it' happens. And then there are starting loads and maximum loads; for the 30/06 the difference is 5 grains +/- very little.

F. Guffey
 
One of the symptoms of "shooting 5.56 in a 223 chamber" is primers popping out into the mechanism of an AR and jamming the trigger up tight. That symptom is better explained by a secondary explosive effect caused by using a bulk grade powder too slow for too light of a bullet causing a pressure wave rebound to hit back into the cartridge brass after the bullet has passed the gas port and the bolt has unlocked.
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The only time a primer can leave my case heads is when the bolt face does not support the case head. In my chambers there just isn't enough time for the gas to run back and forth and turn around etc..

F. Guffey
 
Unclenick,

You wrote. In any event, keep in mind maximum proof pressure for your rifle is 148% above the usually given maximum pressure, and your gun has to tolerate that without damage (though not a steady diet of it). Also, that maximum pressure isn't a maximum in the usual sense of being an absolute, not-to-exceed limit. What is given as a maximum pressure in manuals is a number SAAMI calls the Maximum Average Pressure (MAP).

Unclenick, I need a little more explanation on the above reference, especially the 148 percent figure. What is the relationship between 148% and the maximum charge for any given recipe? You may have given me the answer in your response. Bear with me, the Mensa society isn't knocking on my door.

Jimro, so I'm not really concerned about the rifle blowing up in my face by using 5.56 in a 223 rifle. Is this what you are saying? To keep it simple for me, I have never fired 5.56 in my 223 and have no plans to do so. I guess I've been afraid of the pressure differences. Another reason for not using 5.56 is, I reload and I don't want the extra step of reaming the primer pocket or figuring out how much to reduce a recipe powder charge because of thicker walls.
 
It is too bad the definition of the difference is not described as a narrow window. These things do not lock me up because my military cases become once fire after firing.

And I sort by head stamp and I compare, if there is something I do not like doing: I do not do it. When it comes to doing something to the primer pocket I have at least 3 different ways of doing it.

F. Guffey
 
Jimro, so I'm not really concerned about the rifle blowing up in my face by using 5.56 in a 223 rifle. Is this what you are saying? To keep it simple for me, I have never fired 5.56 in my 223 and have no plans to do so. I guess I've been afraid of the pressure differences. Another reason for not using 5.56 is, I reload and I don't want the extra step of reaming the primer pocket or figuring out how much to reduce a recipe powder charge because of thicker walls.
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Your rifle won't blow up, not from shooting even proof level 5.56 loads in your 223 rifle. The worst that can happen is a stuck case, which will happen with lower pressure loads too for other reasons. A stuck case can be from work hardened brass even with SAAMI spec 223 load.

Milsurp 5.56 brass is well within the "normal" 223 Rem brass internal case volume range, the "thicker walls" myth just doesn't seem to die though. Buy a couple thousand processed 5.56 brass from someone like Jeff Bartlett gibrass.com and load enjoy years of good reloading. Jeff processed a lot of a couple thousand for me a few years back and I've been very happy with them for shooting High Power from AR-15s.

You should always do a load workup when changing components, or powder lots. But don't worry about 5.56 in your Savage, it's not an issue.

Jimro
 
From the reading I've done, this is my understanding of Federal .223 headstamps. ATK owns Federal, and also runs the Lake City ammo plants for the US government.

FC and 2 digit date code- Lake City produced
FC, .223 headstamp, with 3 or six dimples on base- Lake City produced
FC, .223, 2 digit date code- commercial Federal produced in Minnesota, such as Gold Medal Match
FC, .223- commercial Federal produced in Minnesota

You don't need to have any worries about using 5.56 brass in a .223 chambered rifle. Notice I said brass. Ever notice that nobody makes a 5.56X45mm die set? The brass is identical dimensionally. Same diameter, same neck angle, same OAL, same trim length. Some variance is present in internal capacity.
 
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