AR15.Com Archives
 5.56 vs 223 Case Capacity
steve4102  [Member]
6/29/2010 5:49:33 PM
How many of you have compared case capacity of your 223 Commercial brass to your 5.56 Military brass and what did you find? I have always read that 5.56 brass has substantially less case capacity and should be loaded down a grain or two. The I read this 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.

So I checked some of my brass for myself. I weighed five cases of each type, Remington 223, GFL 223 and LC 5.56 and took the average of each type. Then I filled the cases with H20 and weighed them again. Here is what I found.

Rem 223 = 29.9gr H20

GFL 223 = 29.0gr H20

LC 5.56 = 30.4gr H20

So, for my lots of 223 and 5.56 it is clear that my 5.56 has more case capacity than the 223. Anyone find similar results?

Thanks


Paid Advertisement
--
AeroE  [Moderator]
6/29/2010 6:34:25 PM
Check more cases. Winchester, WCC, and Lapua are virtually identical to LC brass. All of them vary slightly from lot to lot, and all of them vary over time so it's a good idea to weigh your new cases occasionally to avoid a surprise.

More internal volume is good. That can be exploited to launch bullets faster without sky high chamber pressures.

steve4102  [Member]
6/29/2010 6:42:25 PM
Thanks, I also found this.
AeroE  [Moderator]
6/29/2010 7:05:01 PM
There's a list over on www.6mmBR.com, too.

Eric802  [Team Member]
6/29/2010 8:25:30 PM
Originally Posted By steve4102:
Thanks, I also found this.
http://i2.photobucket.com/albums/y17/steve4102/casecapacitiesresized.jpg


You beat Molon to posting his own chart. The whole "you have to download for 5.56 brass" thing is one of his pet peeves.
TeeRex  [Team Member]
6/29/2010 8:28:13 PM
Seen it before, but its good info.
dryflash3  [Moderator]
6/29/2010 9:37:02 PM
Originally Posted By Eric802:
Originally Posted By steve4102:
Thanks, I also found this.
http://i2.photobucket.com/albums/y17/steve4102/casecapacitiesresized.jpg


You beat Molon to posting his own chart. The whole "you have to download for 5.56 brass" thing is one of his pet peeves.


Yes it is, and Molon is correct.
JamesP81  [Member]
6/30/2010 2:58:28 AM
Originally Posted By Eric802:
Originally Posted By steve4102:
Thanks, I also found this.
http://i2.photobucket.com/albums/y17/steve4102/casecapacitiesresized.jpg


You beat Molon to posting his own chart. The whole "you have to download for 5.56 brass" thing is one of his pet peeves.


I'm guessing that probably grew out of the need to download 308 loads when used in rifles like the M14/M1A which aren't rated to handle full power commercial loads. However, the dynamic between military and commercial loads in 308/7.62 and 223/5.56 are two completely different things.
ViniVidivici  [Team Member]
6/30/2010 3:38:22 AM

Originally Posted By steve4102:
Thanks, I also found this.
http://i2.photobucket.com/albums/y17/steve4102/casecapacitiesresized.jpg

Thank you for posting that. That's EXACTLY what I thought of when I read the OP.
Eric802  [Team Member]
6/30/2010 9:38:10 AM
Originally Posted By JamesP81:
Originally Posted By Eric802:
Originally Posted By steve4102:
Thanks, I also found this.
http://i2.photobucket.com/albums/y17/steve4102/casecapacitiesresized.jpg


You beat Molon to posting his own chart. The whole "you have to download for 5.56 brass" thing is one of his pet peeves.


I'm guessing that probably grew out of the need to download 308 loads when used in rifles like the M14/M1A which aren't rated to handle full power commercial loads. However, the dynamic between military and commercial loads in 308/7.62 and 223/5.56 are two completely different things.


Exactly. People took the .308 v. 7.62 issue and tried to turn it into something that applied universally to military cases.
steve4102  [Member]
7/1/2010 12:41:24 AM
Thanks for all the help.

I have another question about 223/5.56 case capacity. According to "design specs" the 223 has an internal capacity of 28.8gr of H20 while the 5.56 has 28.5gr. as almost no 223 or 5.56 brass fits into this category I was wondering, is this design spec capacity just a Minimum case capacity or is all the brass manufactured for both just way over specs?
AeroE  [Moderator]
7/1/2010 11:29:33 AM
Originally Posted By steve4102:
Thanks for all the help.

I have another question about 223/5.56 case capacity. According to "design specs" the 223 has an internal capacity of 28.8gr of H20 while the 5.56 has 28.5gr. as almost no 223 or 5.56 brass fits into this category I was wondering, is this design spec capacity just a Minimum case capacity or is all the brass manufactured for both just way over specs?


Where did you come up this "spec" capacity?



steve4102  [Member]
7/1/2010 6:09:05 PM
Where did you come up this "spec" capacity?


I was told that by a guy on another forum that is just bitching at me about 223/5.56 case capacity. My QuickLoad has case capacity in H20 for 223 at 28.8 and 5.56 at 28.5gr H20. I tried to find any kind of official case capacity list, but came up empty.

Thanks
Paid Advertisement
--