Case Capacity, Military 5.56 vs commercial.223

[ARKLITE881South]

Tell me your thoughts on the case capacity of the 5.56 vs .223. I've always heard/read to start at 10% less with you load, when loading a military 5.56 case. I've been loading a while, 40yrs + and have always loaded by this rule. Now, a couple of guys i know who have been loading maybe 4 months, tops, are trying to tell me, they read in a loading manual there is no difference between the Mil 5.56 and the .223 commercial case capacity. I've made it all these years with all 1o fingers, and both eyes, and i don't plan on changing my loading habits. I was just wondering what you think. Heavy mil spec brass vs, commercial brass is the issue. From my point of view they can load it how ever they feel safe loading it. They like to load around max loads, or push it as far as they can with commercial brass in .223

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[Darkker]

There is no more variance, than is normal manufacturing variation.

Of the usual suspects who actually make their own brass, I called about this very subject last summer. The answer is the only difference is the stamp. Which from a production standpoint makes total sense. Why switch runs, when you can build only one product, kill two birds with one stone.

 

[rick benjamin]

I once was an "arrogant" reloader, till I bought and used a chronograph.
Still gives me a shiver, re-counting my fingers.
<broken link removed> after 18 years of shooting
<broken link removed>
My uncle Jack reloaded for my Dad's Win70 .270, hot loads, 40 years worth.
The barrel metal migrated with the bullets until the muzzle choked (like a shotgun).
Gunsmith cut off the last 1.5" to fix that problem, now the bullet leaves before powder is done burning.
Massive muzzle blast and tongue of fire!

 

[deen_ad]

Here are two articles that should shed some light on the cases.

http://www.gundigest.com/ammunition-reviews-articles/223-vs-5-56
http://www.humanevents.com/2011/02/15/223-remington-vs-556-nato-what-you-dont-know-could-hurt-you/

 

[AMProducts]

I pretty much never push anything at a "max load" anyways, since generally I'm loading volumetrically (using charge bars), I try to make sure I'm no closer than .4gr to the max. Now at the same time, load data that's published today is much tamer than it was way back when. So a published "max load" may still be 3k-PSI under PMAX. While this is good for commercial loads, if you're really trying to squeeze all the performance possible, you can get higher, but this really requires a delicate touch, a lot of experience, and good test equipment.

I generally want the most accurate and reliable ammo I can make, these two quantities are the inverse of maximum velocity. At the same time, usually a maximum load only gives you a few hundred extra feet per second in a rifle, so for a 10% hit to your pressures, you're only getting 3% more velocity, it's hardly worth it in my opinion and as such I stay away from it.

To your original question, most of the manufacturers these days all have the TDP for the 5.56 round, and are going to make their tooling to make more or less the same dimensions. As you can see from Darkker's post, the variance is 1.2gr of water... that's a very tiny variation on the order of fractions of a drop.

So to combine these observations... I load all brass the same, however I don't push maximum loads.

 

[SinisterSouthpaw]

ok, I'll bite. what does the chronograph post have to do with this thread? Maybe I don't understand, being never got beyond semi-arrogant?

 

[Nickb]

You check actual velocity to published velocity, if you think you're loading a "safe" load, say 3200 fps according to published velocity but when you check what your load is actually doing 3600fps, something is off.

 

[AMProducts]

ok, I'll bite. what does the chronograph post have to do with this thread? Maybe I don't understand, being never got beyond semi-arrogant?

For most people, velocity and brass deformations are the only means available to surmise chamber pressures. One of the critical factors in determining burn rate is the initial volume of the cartridge case, as if you load two rounds identically, yet the volume of each case is different, it will affect how the powder burns. The differential between the two cases, will result in a differential between the two rounds in terms of pressure and thus velocity. However, the differences will always be slight.

 

[SinisterSouthpaw]

THOSE differences are not only unpredictable, but the samples required to make chronography a worthwhile tool in any respect whatsoever as relates to downrange performance or any other aspect of shooting disciplines are neccessarily so large as to make them impracticable if not impossible, and to try to relate them to case capacity is ludicrous in the e xtreme, especially as practiced byt he casual shooter who typically tries to make samples of 10 to 30 shots yield data that would require 100 to 1000 samples (shots) to evenb egin to yield useful information.

 

[Darkker]

No, not really.
In terms of the changing burning rate due to volume shift: extruded powder has its burning rate controlled by geometry, on purpose.
Loading extruded powder by volume, NOT weight; will keep a very tight burning rate.
Any nominal shift in burning rate due to case volume will be a minor difference. Whereas if you loaded by weight only, and had a massive capacity shift, you can have some very noticeable changes.

In terms of using a chronograph to track those differences, you can easily follow changes. The ES & SD numbers can speak volumes to that point, if you track them; even on a relatively small scale.

In terms of the downrange results, a chronograph is also incredibly helpful for distance shooting. Again the ES/SD numbers are helpful for groups. Also with an accurate starting velocity, you can more accurately dial your corrections for drop and trajectory at distance. Does the difference at 200 yards matter? Depending upon what you are doing, maybe not. But if you are looking for PRS shooting, or just doing tight groups at distance; it is invaluable.
For my 308 shooting to 1760, you better know your true starting velocity. Once you get dialed in, you can use it down range to check against stated BC numbers. For me, I find that above supersonic, the G7 numbers are more accurate(not really a surprise), but once you cross transsonic, G1 becomes more real.