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Originally Posted by nemesiss45
I have not measured it, but I've heard the military brass has a smaller case capacity and will thus produce higher pressure than a comparably loaded .223 case. you should be safe working up from a starting load from a manual. you will notice no manuals differentiate between the two (5.56 and .223)
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This is another myth that will not die. Military 5.56 brass does not have less internal case capacity then civilian 223 brass. In fact most 5.56 brass has More case capacity the 223 brass.
This is from Sierra.
The conventional wisdom to reduce loads with military brass is familiar to most reloaders and is generally good advice. The rationale here is that the military cases tend to be somewhat thicker and heavier than their civilian counterparts, which in turn reduces capacity and raises pressures. This additional pressure normally requires a one or two grain reduction from the loads shown in most manuals or other data developed with commercial cases. While this is most often the situation with both 308 Winchester and 30-06 cases, it is less true with the 223 brass. We have found that military cases often have significantly more capacity than several brands of commercial brass. Again, take the time to do a side-by-side comparison of the cases you are working with and adjust your load as needed. There may be no need for such a reduction with the 223. Know your components and keep them segregated accordingly.
Link.
http://www.exteriorballistics.com/re...sgunreload.cfm
Here are a couple of charts where internal case capacity was actually tested. You will note that the Military 5.56 brass carried the Highest capacity.
I tested my own brass and this is what I found. Note, the LC 5.56 brass had the highest capacity of the three.
GFL(223) dry weight-102.4gr
With H20-131.4
Case capacity in grains of H20-
29gr
Remington(223) Dry weight-95.2gr
With H20-125.1gr
Case capacity in grains of H20-
29.9gr
LC(5.56) Dry weight-96.3gr
With H20-126.7gr
Case capacity in grains of H20-
30.4gr.
To answer the OP, there is basically no difference as far as case capacity is concerned. Their will be no difference in external dimensions once you run them all through your Full Length sizing die and trim.
The only difference is the crimped primer, once you remove the old primer you must remove the crimp, once.