What does "hot" brass mean?

[Zak Smith]

I have two data points that confuse me:

1. With a "mild" 8x57JS load (150gr @ 2700 fps, 52gr Win748), the fired cases are thermally cool enough to handle immediately after firing. (Gun is a k98.)

2. With a "mild" .308 load (150gr Nosler BT, 2600fps, 45gr Win748), the fired cases are so thermally hot that they burn my fingers if I try to pick them up after firing. (Gun is a FAL.)

What does the temperature of the fired brass indicate?

-z

 

[Southla1]

They all feel fairly hot to me, specialy if you get one down the neck , but basiclly its pressure. The .308 is one of the highest pressure rounds around, while the in an 8mm the "mild" load is very mild and low pressured due to all the older Mausers out there. A mild load in 308 may be at or approaching 50,000 CUP while a mild load in 8MM may be in the high 30,000 CUP range. The 308 case being smaller it takes less powder to acheive a higher pressure.

 

[Mike Irwin]

Well, just off the top of my head, to me it would mean that in your 98 a lot of the heat is being wicked out of the brass by the surrounding chamber.

Because extraction is so rapid in your FAL, most of the heat absorbed by the brass stays in the brass, I'd bet.

 

[Zak Smith]

That's good insight, Mike. I hadn't thought of that.

Another thing I was reminded of was that the FAL barrel was probably hotter than the k98's barrel.

-z