Water Capacity

[79M1a-texas]

I was reading “Rifle Sporting Firearm Journal”, Nov 2008 publication and on page 16 they listed the following .308 Case Weight Chart:
Case- Weight (grains)- Water capacity (grains)
Federal - 177.80 - 53.4
Remington - 166.24- 54.0
Winchester- 157.05- 54.1
LC 84 - 180.20 - 54.8

If the “military case’s extra weight comes from its somewhat thicker head and extractor groove compared to the commercial cases”, then why would it have the largest water capacity?

 

[BobinNC]

Re: Water Capacity

So according to the “Rifle Sporting Firearm Journal” LC brass has 1.45% more capacity than Rem Brass even though it weighs 7.7% more. Like maybe, just maybe, they are wrong?

Not saying they are wrong, mind you, but the physics of such a happening is staggering....If your measuring apples to apples....Federal and the others putting aluminum in their cases?

Intrigued,

Bob

 

[Grump]

Re: Water Capacity

External dimensions on all those charts we've looked at for decades DON'T include the tolerances for thickness of the extractor rim or variances in the extractor groove.

There also *may* be some differences between brands attributable to differences in alloy make-up, but I doubt that would be more than 2 grains in .308-size cases. I don't have the curiosity/motivation to start calculating densities of copper and zinc to see whether it would make any difference.

Keep in mind that a mere 1% variation in weight here is about 1.6 to 1.8 grains. Measure your brass before and after trimming and put that into perspective.