Using .223 rem Data in 5.56 NATO brass.

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RTF2

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I am wondering if anyone has any experience in using .223 rem data in 5.56 NATO cases? I know the cases are a bit thicker, but I see no reason why using the lower pressure load data would hurt. I use adjusted data for my .357 loads so they're more like .38spl, just thinking I may be able to put the 5.56 NATO brass to good use. Using 55gr FCP BT with 22gr of IMR 3031. Any opinions?

A concern of mine is the lower pressure not fully expanding the case neck on the thicker brass for a good seal, letting gas escape which can be dangerous.

Thanks,
Trevor
 
I don't think there is enough difference to matter in 5.56 and 223 brass.
There is in 7.62x51 and 308 commercial brass.
 
Do it, but work your load up as usual. Don't just use a hot load that worked before. I find that optimal loads vary between military brass and .223 but I never had any pressure problems.
 
No problem at all. I give both the same level of preparation and consider them interchangeable at .223 levels. I've tested various .223 brass at 5.56 levels and had zero issues as well. I do keep them reserved for their respective loads now because why not use the existing markings.
 
Below are .223/5.56 case capacities and case weights and the majority are very close in capacity.
"BUT" Lake city military 5.56 cases are made of "harder" brass than .223 cases. (Ford Truck Tough)

NOTE, tooking at the chart below the top Lake City case has a case capacity of 30.6 and and the bottom old Lapua case has a capacity of 28.0. And with the same 25 grain charge of H335 and a 55 grain bullet there would be a 6,000 psi increase in chamber pressure with the Lapua case with less capacity. (Quickload data)

Also the older .223 rifles with a 1 in 12 and 1 in 14 twist rate will have a shorter throat. And if military ammunition is fired in shorter throated .223 rifles you will have a 5,000 to 6,000 psi pressure spike. "BUT" my Savage .223 bolt action with a 1 in 9 twist has a longer throat than my AR15 rifles do.

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The major difference in .223 and 5.56 cases is military cases are made of harder and stronger brass. And not thicker like 7.62 NATO cases because it would cut down on case capacity too much with 5.56 cases.

How Hard is Your Brass? 5.56 and .223 Rem Base Hardness Tests
http://bulletin.accurateshooter.com/2014/05/how-hard-is-your-brass-5-56-and-223-rem-base-hardness-tests/
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Also military cases have thicker flash hole webs that add strength to the base of the case. Meaning the primer pockets can take more pressure and will last longer before stretching.

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