A few of the posts here got me to do some more unscientific, anecdotal observations. Especially when it comes to a comparison of capacity between the aluminum and brass cases. From my calculations, such as they are, I found that the aluminum cases hold 12.7 grains of water. The brass cases hold 13.6 grains of water. Of course I used the CCI aluminum cases and I used Federal brass cases. I weighed the cases dry and then weighed them filled with water. I did it with 10 of each and took an average. I knew the aluminum would be lighter but it surprised me how much lighter they actually were. The aluminum averaged 23.1 grains dry and the brass was 58.2 grains. More than twice the weight as the aluminum. I sectioned two cases. Here's a photo.



The brass is on the right. I didn't do any measurements, but the head thickness looks to be about the same. The walls of the aluminum are much thicker than the brass and the thickness extends father up the case. This is where the aluminum looses volume to the brass. I'm guessing that this is how they make up for the lack of elasticity in the aluminum compared to the brass. It's a pretty elegant solution if you ask me. So the verdict in my courtroom is: yes, the aluminum has less volume, therefore, maximum pressure loads for a brass case is going to be over pressure in an aluminum case. How much? I guess if you are an engineer you could figure out the difference. I think it would be enough of an overpressure that I wouldn't go anywhere near it. Another observation is the size of the flash hole. It's much bigger than the brass case. I'm standing by my conclusion that it is the reason I had primer flow. The larger hole allowed more pressure to enter and it pushed out the primers. It's not a big deal to me. I've had way worse on 357 magnum loads that were well within the published data. So how do the ammo companies get away with using the aluminum case? Mostly it's in the way they go about building their loads. Unlike a handloader, who starts with a powder with a known pressure curve then adds components to achieve a result, they start with a specification and make a powder to achieve their goal. Lets say they want to make a 115grain bullet go 1200 fps at a certain pressure level. They figure out the burn rate they need then make a powder that burns at that rate. That's one reason why you should never use powder pulled from factory ammo. Just because it looks like Bullseye, it probably isn't. So now the 800 pound elephant. What about that NR stamped on the case head? What about the fine print on the box that says "DON'T EVEN THINK ABOUT IT!"? When CCI first came out with aluminum (They weren't the first. The military had been using it for all sorts of ammo for many years.) the cases were Berdan primed. This was because they didn't want anyone to do what I just did. At some point, they figured they could up their profit margin by standardizing primers and the Boxers came on the scene. So what about their liability if someone blows themselves up reloading an aluminum case? Did it suddenly disappear? Of course not. Here's what I think changed. They had about 25 years of aluminum manufacturing under their belts. I would be shocked if they didn't factor reloading into their risk assessment before they changed over to Boxer primers. I think they concluded that what I just experienced would be the most likely outcome. So long as due diligence is followed, the risk of damage compared to brass is small. They're not going to come out and bless reloading aluminum, but it's not a big enough problem that they have to make the cases so that it's impossible to reload them. If the cases were so fragile that they can't withstand the reloading process, they would make the primers square if they had to to stop people from trying it. In the world of civil suits and settlements, that NR on the case head is almost meaningless. Everyone makes their own decisions, for the most part, and if you like playing around with this stuff I think you can do it safely. I'm not going to scrap my brass cases but it is an interesting (To Me) topic and it's nice to know that it can be done if there's ever a brass embargo.