Need advice for 5.56mm load data

I have a large quantity of Federal XM193/5.56 which I plan on reloading. Do I use the load data listed for the .223 Remington cartridge in my Lee relaoding manual?

My concern relates to difference in volume between the two casings. If the .223 data is used in the 5.56 casing will it cause excessive pressure and a dangerously hot load?

I searched, but did not come up with any useful information; only explanations and debate on the differences between the two.

Any advice would be greatly appreciated.

Thanks!!

Yes, use the 223 data.

as far as the differences in cases go...I did a little test between LC 5.56 brass and Winchester 223 brass.

I resized one of each and trimmed them both to the same length. Then I compared the cases H2O capacities by filling each one a drop at a time until the water was level with the case mouth. Then poured the water from the case into the pan on my digital scale. I was amazed that both cases held the same amount of water....within 0.1gr

I would suggest doing a test like Hawcer suggested with your brass. I too have found the differences to be pretty minimal. Those minimal differences can be very bad if your on the high end or max charge range though.

5.56 data is going to have more pressure than 223 data, so you should be fine using 223 data in 5.56, but don't go the other way without proper load development. Also take into consideration if your loading for a bolt or an AR, as an AR will require additional pressure.

I remember when I first started loading for my 223 I was getting velocities in the low 2000 range but book showed I was supposed to be in the low 3000. Of course I was using bolt action data, when I switched to the AR data by Sierra my groups improve and I was getting better FPS readings.

http://accurateshooter.net/Downloads/sierra223rembolt.pdf
http://accurateshooter.net/Downloads/sierra223ar.pdf

Most USGI 5.56mm brass has case capacities right in the middle of the pack, as it were, when compared to commercial brass. I stress USGI, because some foreign milsurp 5.56mm brass is much, much thicker than USGI brass.

USGI 7.62mm NATO brass does have a lower case capacity than commercial American .308 Win brass, so you definitely need to heed the warnings to reduce the powder charge and work back up as pressure indications permit.