Quote Originally Posted by Silvercrow1 View Post
In my quest to get the best loads possible (for me, anyway) I am looking at case capacity for my .223 Rem reloads. There are a couple of websites that give case capacities re: volume of water. I just bought 100 Lapua Match cases- empty weight they are significantly heavier than the LC 07, LC 11 and .FC. I have been using. I realize internal capacity is what matters regarding weight. Some postings on the internet indicate that Lapua Match cases had less vol. using water weight measure- but I intend to weigh them myself.

SO logic tells me the less internal capacity, the more pressure, correct? So I'd need to reduce loads somewhat to attain the same results when going to a case with lesser internal capacity?

I've read here and elsewhere that when using military brass (thicker walls, less internal space) to reduce loads by 10%. I generally do not load to max weights anyway.

IS THERE A FORMULA available to tell how much reduction is needed to maintain equal pressures when various cases? In a 2007 thread here one of our members attached a link for just this thing...but the link did not work. Maybe I'm not searching with the proper words- but I am finding nothing. Not trying to be lazy- just more efficient in re-working loads. For instance, I use 25.1 GN Win. 748 behind a 50 Gn. Vmax bullet in my LC11 cases and get consistently great (less than 1/3") groups. If I do the 10% reduction thing, I'd have to start back at 2.3 / 2.4 grains?

Any help would be appreciated. THANKS!

Brian


Silvercrow1

American military 5.56 cases made at Lake City are not made thicker, they are made harder in the base. If LC 5.56 cases were made thicker like LC 7.62 cases it would cut down too much on their internal capacity. The chart I posted from AccurateShooter.com shows that the vast majority of .223/5.56 cases are very close in case cpacity.

If you look at the case weight chart you will see Lapua cases only varied 1.2 grains in weight, and the Winchester cases varied 6.5 grains in weight. "BUT" both the Lapua and Winchester cases averaged 30.1 of case capacity, meaning the Lapua cases are more consistent in weight and internal volume and thus equaling better quality and accuracy.

The quickload information below was made up for loading my AR15 rifles "before" I got my chronograph and are "ballpark" guesstimates. Meaning the burn rate in Quickload was not adjusted using a chronograph so the pressures and velocities will not be corrected by matching velocities. The charts were made up to see how much the pressure and velocities would vary between cases with a internal volume of 30.6 and 28.0 grains of H2O.

Below a Lake City case with 30.6 grains H2O capacity, 25 grains of H335 powder and a Hornady 55 grain FMJ bullet.



Below the same exact load using a case with 28.0 grains H2O capacity and a increase of 6,000 psi in chamber pressure.



The purpose of the charts was to see how much pressure and velocity variance I would have using mixed brass at the extreme ends of capacity with my AR carbine. With the Lake City, Federal and Remington cases I'm using with my load of 25 grains of H335 the case capacity only varies less than 1/2 a grain in capacity and good enough for practice ammunition with my AR15 carbine.

Bottom line, I also have a Stevens 200 .223 bolt action and do not use mixed brass and use brass from the same manufacture for better uniformity and accuracy. You are always better off using uniform brass and if you try using mix brass your group sizes will increase. Uniformity goes hand in hand with accuracy and I'm happy with three inch groups with my AR15 carbine with "mixed" brass and happy with the 3/4 to 1/2 inch groups with my Stevens 200 using uniform brass from one manufacture.

As a side note the vast majority of .223/5.56 brass I buy is once fired Lake City brass, and for the "quality" and price it can not be beat. And when weight sorted and uniformed it is very uniform and far cheaper than Lapua. I'm 65, have chronologically gifted eyesight and drink too much coffee and and this is just a opinion of a old fart.