Any one good at firearms ballistics?

[gyrene81]

the dimensions of the cases between the 2 rounds are too different to be interchangeable...where are you finding 5.56mm/.223 rem cartridges being turned into .30 carbine blanks? i could see it maybe with a hollywood modified receiver or an adapter of some sort.

[-ammo-]

Buy a reloading manual before you blow something up.  There are so many variables that can go wrong.  No! I'm not going to list them for you.   Do it right or donate some fingers where so many have before!

Oh...and when you create your FLESH EATING MONSTER get a chrony to test it so you know that you have it under control.

Very good advice.  Also, never exceed published maximum loads.  Never start a load at the published maximum charge.  This is especially important when loading for a "less than modern" firearm.  Watch for the the tell/tell excessive pressure signs (flat primers, etc).  Creating your own wildcat round means you have to be extremely careful.

Forgive me if I am preaching to the choir.

[Kenne]

the dimensions of the cases between the 2 rounds are too different to be interchangeable...where are you finding 5.56mm/.223 rem cartridges being turned into .30 carbine blanks? i could see it maybe with a hollywood modified receiver or an adapter of some sort.

(Image removed from quote.)

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are the dimensions of 223 rem brass different to 556 mil brass?

[gyrene81]

are the dimensions of 223 rem brass different to 556 mil brass?

very slightly, at the neck/shoulder...case is thicker on the 5.56 mil as well.

[SmokinLoon]

very slightly, at the neck/shoulder...case is thicker on the 5.56 mil as well.

Internal.  The key word is internal.  If the typical loadings are used then the shooter has no worry using either brass for any role.  The biggest difference is the rigidity of the military brass (5.56 NATO), it needs to be slightly more stout in order to be used and abused in military rifles and machine guns.  A reloader typically can not get as may uses out of 5.56 NATO brass simply because of case head separation issues.  Commercial .223 Rem brass is softer and is thinner per say, and is normally used out of bolt action guns which have slightly "tighter" chambers.  However, it is 6 one way and a half dozen the other because eventually both kinds of brass will have issues.  I simply separate brass by commercial and military and load accordingly, which for me typically means -3 to -%10 of the listed "max" loadings.  If I'm pushing the pressure a bit high for purposes of velocity, I only so so with the Savage 112FV.  The AR15 gets the typical military recipe.