Author Topic: Pressure Questions (Read 661 times)

flabbydan · « **on:** February 21, 2004, 11:49:34 AM »

:? I was pondering whether to get a deer rifle chambered in 260 Rem or 7-08 Rem. I realize that they are ballistically very similar, and either one would be a near-perfect deer caliber, but why is it that the 260 can be loaded to such a high pressure (60,000 CUP) compared to the other cartridges based on the 308 Win (52,000 CUP).

Iowegan · « **Reply #1 on:** February 21, 2004, 01:30:29 PM »

Flab, Both the 260 Rem and 7mm-08 were based on a necked down 308 case. With near identical case deminsions and powder charges, the restricted diameter of the case mouth is what drives the pressures up about 15%. Throat life in the 7mm-08 is much better than the 260 due to this very condition. Also, the 260's are very fussy. A couple tenths of grains makes a significant difference in accuracy, whereas the 7mm-08's are a lot more forgiving.

flabbydan · « **Reply #2 on:** February 21, 2004, 04:13:29 PM »

I see what you're saying about the smaller diameter of the 260 causing higher pressures, but then why does the 243 have only a 52,000 CUP pressure limit? You made a good point about the throat erosion. I never thought of that.

Iowegan · « **Reply #3 on:** February 22, 2004, 07:37:36 AM »

You'll notice the 243 shoots a much lighter bullet than the 7mm-08 or 260. Bullet weight has a giant effect on chamber pressure, even if the "hole" is smaller.

flabbydan · « **Reply #4 on:** February 22, 2004, 10:21:51 AM »

Sorry I ever doubted you! :oops: I feel like a moron. :lol:

onesonek · « **Reply #5 on:** February 22, 2004, 10:43:01 AM »

Quote from: flabbydan

:? I was pondering whether to get a deer rifle chambered in 260 Rem or 7-08 Rem. I realize that they are ballistically very similar, and either one would be a near-perfect deer caliber, but why is it that the 260 can be loaded to such a high pressure (60,000 CUP) compared to the other cartridges based on the 308 Win (52,000 CUP).

Are you sure you aren't confusing psi against cup? Most everything I'm seeing list the 260 in the neighborhood of 58-59,000 psi.

flabbydan · « **Reply #6 on:** February 23, 2004, 04:15:56 PM »

OOPS :oops: Now I really feel stupid!! That's quite a detail I overlooked. If anyone needs me, I'll be looking in the toilet for my brain cells :lol: .

Iowegan · « **Reply #7 on:** February 23, 2004, 06:20:14 PM »

Flab, Don't beat yourself up. We really are here to help one another, even if tact and diplomacy aren't our strong points. Lots of shooters read these posts and learn quite a bit. When terms like psi or cup are used, we just want to make sure some newbee doesn't go off and blow up a gun. Your questions on pressure were good so don't be afraid to come back.

onesonek · « **Reply #8 on:** February 24, 2004, 01:22:25 AM »

Another thing to remember SAAMI really don't set standards,(well up to a point thet do) they're more of a testing and registry of documentation for the industry. Point being, what ever the mfg'r supplies is what goes. Remington is noted for underloading it's ammo. That's why you see difference's in pressure rating( regardless cup or psi) on the 308 case family. Rem. 260 and 7-08 is loaded lower than Win. 243 and 308.
And like Iowegan said, you cant learn without asking. There are no stupid questions. When in doubt ask, the alternative may hurt, or worse.

JimInNJ · « **Reply #9 on:** February 24, 2004, 01:40:58 AM »

I wouldn't worry much about throat erosion in a .260 deer rifle, unless you plan to shoot fourty or fifty deer every weekend. :lol: In that case you may need to rebarrel in a couple of years.

Silhouette shooters are fond of the .260 and usually get a few thousand rounds out of a barrel.

Just be careful to give it a chance to cool down a little between shots when you are at the range.

- Jim