Case capacity question

[bdbrown66]

Here's one that's got me thinking, and I haven't had a chance to get some real-world evidence one way or the other.

I usually load Federal brass for my .243. However, the most recent load (Sierra 85gr BTHP) I worked up using Hornady brass. I ran the ladder and found the sweet spot, then loaded up a batch of them. And then I got to thinking about the Hornady vs. Federal brass. I weighed several of each empty, and picked one of each that seemed to be representative of the group. Then I filled each with water and weighed them again. I don't have the numbers right in front of me, but the Federal held 1.1gr more water than the Hornady.

Now, here's the question: Is that capacity difference enough to make a "real-world" difference in how that load shoots? If I were to reproduce this load in the Federal brass, should I expect it to shoot to the same POI, and with the same accuracy, as the Hornady?

I know that the only way to know for sure is to load some of them and try it out. I'm just wondering what others have seen with this degree of case capacity difference.

Cheers,
Brian

 

[TackDriver284]

One thing for sure is the less capacity case will have more pressure if the powder charges are the same as the larger case capacity. For one grain difference, its not much difference. I have seen different case brands have different POI, mostly depends on case volume.

 

[kraky1]

I will enter my guess and say it might and it might not.
I was at the shooting range today with my 7mmo8 Scout rifle which is a break open single shot.
It doesn't like hot loads and medium loads are about as far as you want to take it or it will start stringing vertically.
I found loads with Winchester brass and federal brass with the exact same loads were doing the exact same speed.
The Winchester brass is quite a bit roomier and my only explanation is because they were medium loads, case capacity didn't matter much.
The other thing that was kind of crazy and it is specific to this gun is that the federal brass was much more accurate.
I would normally think of federal as being a softer brass and it might stretch easier but what I find in checking headspace after these loads were shot was the Winchester brass stretched out more and I think it puts a little more stress on the frame of the gun versus the federal brass.