down sizing brass... pressure
- Thread starter WhelanLad
- Start date
vagrantviking
CGN Ultra frequent flyer
- Location
- Southern Alberta
For sure.
In fact necking down can lead to the brass being too thick in the neck and too much tension particularly in a tight chamber.
In fact necking down can lead to the brass being too thick in the neck and too much tension particularly in a tight chamber.
WL.........unless your 7-08 chamber is a special cut match chamber there is no problem at all going from 30-28 cal or even 30-26........no sweat, no issues. I have even done several hundred rounds of military 308 down to 243 and never had to turn necks.
This is for the kimber? All mine have had chambers on the tight side. Here's the test, neck them down and check them in the chamber, if all good then load them up and fire them. Then check them with an appropriate bullet, they should slide through the neck with no resistance or at least very little resistance. If you can just about load them again without resizing then you need to turn necks.
That's something I used to believe, and I know have said the same thing numerous times. Recent events have changed my position.
I just built a 6.5-300 Win (because I didn't have one). Dummy loads with my necked down brass measured .294" at the necks and reamer was .298". Did a test cut on an old barrel and came out at .298". Perfect right?
Ran through 50 rounds doing some initial load development and when I went to reload those cases the bullets wouldn't fit into the fired cases. Oh, Oh. Measured up everything, and the cartridges were going into the chamber at .294 and coming out .294. Well that won't do, so I packed ammo, fired cases, rifle and reading glasses and made the 15 minute drive over to my gunsmith. Explained everything, and the gunsmith agreed that I wasn't blind and could read a caliper. He mentioned that the size of the fired necks didn't necessary mean much. He also pointed out that we had checked all that before the blank ever got chucked up. I couldn't argue that either, since I was there. Anyway, there's two things you can't argue with, a station wagon full of nuns and a chamber cast. We poured a cast and the throat was indeed .298".
Conclusion? Fitting bullets into fired cases might prove they are safe. The bullets not fitting into the fired cases might not prove anything. Brass just might do whatever it wants. I also concluded that I was really glad I hadn't stormed in with righteous indignation and knowing everything.
The story doesn't quite end there. After the cases had been used four times, they now measure a hair under .298 when fired. Just when you think you've unlearned some unfacts, and decided that sometimes this stuff doesn't work, you get confronted with the fact that sometimes it does.
That's something I used to believe, and I know have said the same thing numerous times. Recent events have changed my position.
I just built a 6.5-300 Win (because I didn't have one). Dummy loads with my necked down brass measured .294" at the necks and reamer was .298". Did a test cut on an old barrel and came out at .298". Perfect right?
Ran through 50 rounds doing some initial load development and when I went to reload those cases the bullets wouldn't fit into the fired cases. Oh, Oh. Measured up everything, and the cartridges were going into the chamber at .294 and coming out .294. Well that won't do, so I packed ammo, fired cases, rifle and reading glasses and made the 15 minute drive over to my gunsmith. Explained everything, and the gunsmith agreed that I wasn't blind and could read a caliper. He mentioned that the size of the fired necks didn't necessary mean much. He also pointed out that we had checked all that before the blank ever got chucked up. I couldn't argue that either, since I was there. Anyway, there's two things you can't argue with, a station wagon full of nuns and a chamber cast. We poured a cast and the throat was indeed .298".
Conclusion? Fitting bullets into fired cases might prove they are safe. The bullets not fitting into the fired cases might not prove anything. Brass just might do whatever it wants. I also concluded that I was really glad I hadn't stormed in with righteous indignation and knowing everything.
The story doesn't quite end there. After the cases had been used four times, they now measure a hair under .298 when fired. Just when you think you've unlearned some unfacts, and decided that sometimes this stuff doesn't work, you get confronted with the fact that sometimes it does.
Thanks for sharing that.
Regards
Ronr
Norma. Accuracy was fine right out of the gate, been too busy working on loads for other rifles to finalize these ones but 140 VLDs and 142 LRs are looking good.
DL, I think your experience with those case necks is not the normal experience of most people, including yourself from what you wrote.
I do believe the cartridge design itself had a lot to do with pushing brass forward because of the high pressures involved. One other factor not mentioned here is that when cases are necked down they become longer and need to be trimmed. The opposite occurs when case necks are expanded to a larger diameter.
Also, the neck you describe is very tight IMHO, almost as close as match standards. Sounds like a nice set up.
OP, I have at least a dozen custom rifles with tight chambers. I have never had a problem with any of them as far as chambering goes other than if I don't trim the necks properly. If you're having trouble with your neck diameters it may be time to anneal the cases or turn down the necks with an appropriate tool. It's pretty simple.
When brass work hardens it becomes far less ductile and won't size down in your sizing die. Brass will also flow under pressure. All of this needs to be taken into account.
I do believe the cartridge design itself had a lot to do with pushing brass forward because of the high pressures involved. One other factor not mentioned here is that when cases are necked down they become longer and need to be trimmed. The opposite occurs when case necks are expanded to a larger diameter.
Also, the neck you describe is very tight IMHO, almost as close as match standards. Sounds like a nice set up.
OP, I have at least a dozen custom rifles with tight chambers. I have never had a problem with any of them as far as chambering goes other than if I don't trim the necks properly. If you're having trouble with your neck diameters it may be time to anneal the cases or turn down the necks with an appropriate tool. It's pretty simple.
When brass work hardens it becomes far less ductile and won't size down in your sizing die. Brass will also flow under pressure. All of this needs to be taken into account.
