300 Win Mag shoulder growth

I change over 25 yrs ago to neck sizing my belted mag cases. It stop the case separation and lost of case in 3 to 4 firing. Now getting 10 to 12 firing from the case. These powder loads were about 5 grs over manual loading spec. I would lose them do to primer pockets getting to big. They say there a fix to that too now, and I will try that to see how it works. The other part of this is when I fire the cases I would use a neck sizing die and not completely size the neck. That created a kind of 2nd shoulder in the neck. It reduced the grouping size at the same time. The other item was I cut my necks for thickness and uniformity after full length sizing my case at the time. Head space off the shoulder not the belt. It's isn't that hard to setup. I am looking at gettng some of the peterson 300WM long cases. Which I am going to size down to 7mm RemMag chamber.
There has been alot of changes from that time going forward. I haven't been able to put new practises inplace just yet. Finally I am just about to complete my reloading shack in Montana. Got a long way into finishing it this time around.
It's hell to get old, and having to depend on others.
I have learned alot here, and adding to my reload practises. It will be interesting to see what works or doesn't make any differents.
 
Last edited:
MagnumManiac said:
There is no such thing on a belted magnum…
Headspace is in the belt datum, not the shoulder…
Click to expand...
By SAAMI standards you are correct. I'm not a commercial ammunition manufacturer and do not follow SAAMI specs 100%. I choose to headspace my belted mags on the shoulder just like my other bottleneck cartridges, I even load my 357 SIG ammo to headspace on the shoulder. I'm completely satisfied with my case life and accuracy resizing my brass this way.
 
1mechanic said:
If this is true what causes case head separation?
Click to expand...

Here is how I think about case stretching upon firing. I'm not sure I'm right about any of this, but this is what I think happens.

Upon firing, the firing pin forces the case to the front of the chamber. The front of the case is always softer than the rear of the case, so as the case pressures up, the case walls at the front of the case "grab" the cylinder walls first. Most length stretching of the case walls (to push the case head back to the bolt face) occurs at the rear of the case, because the front of the case walls have already "grabbed" the chamber walls. It's important to limit this stretching at the rear of the case, because that part of the case is work-hardened and won't stretch much before cracking.

In belted magnums, a new case headspaces off of the belt. So the firing pin can't force the case to the front of the chamber, and most stretching occurs in the front of the case, which has been heat treated to ensure ductility. Even 0.030" of stretch at the front of the case should be no problem.

Unfortunately, the SAAMI tolerance for the cartridge belt to case head distance is -0.008 ", so the maximum actual headspace between the case head and the bolt head could be as much as .010" or so, assuming the rifle was set up with .002" headspace against a SAAMI button.

When I build a belted rifle, I buy and dedicate 150 cases to the rifle, and I headspace the rifle using a sampling of those dedicated cases. Typically the bolt of a rifle headspaced that way fails to close on a SAMMI headspace button, suggesting that the case manufacturers I use don't manufacture their cases at the nominal (0.000" tolerance) SAAMI dimension. In any event, I'm confident that stretch at the rear of my cases upon first firing is 0.002" or less.

Also, I have my belted rifle reamers made up 0.010" shorter than SAAMI. That limits the stretch somewhat at the front of the case upon first firing, but more importantly allows subsequent sizings, headspaced at the shoulders, to go all the way down to the belt. I do have to lap 0.005" off the bottom of my sizing die to prevent bottoming on the shell holder though.
 
1mechanic said:
Curious what does cause case head separation?
Click to expand...
excessive headspace or over sizing brass. I have a 350 rem mag encore with a long chamber. Years ago I just FL sized blindly like a lot of guys and never had issues. But the die I had was pushing the shoulders back .018. After 2 firings the brass had separation cracks.
 
Mike Matteson said:
I change over 25 yrs ago to neck sizing my belted mag cases. It stop the case separation and lost of case in 3 to 4 firing. Now getting 10 to 12 firing from the case. These powder loads were about 5 grs over manual loading spec. I would lose them do to primer pockets getting to big. They say there a fix to that too now, and I will try that to see how it works. The other part of this is when I fire the cases I would use a neck sizing die and not completely size the neck. That created a kind of 2nd shoulder in the neck. It reduced the grouping size at the same time. The other item was I cut my necks for thickness and uniformity after full length sizing my case at the time. Head space off the shoulder not the belt. It's isn't that hard to setup. I am looking at gettng some of the peterson 300WM long cases. Which I am going to size down to 7mm RemMag chamber.
There has been alot of changes from that time going forward. I haven't been able to put new practises inplace just yet. Finally I am just about to complete my reloading shack in Montana. Got a long way into finishing it this time around.
It's hell to get old, and having to depend on others.
I have learned alot here, and adding to my reload practises. It will be interesting to see what works or doesn't make any differents.
Click to expand...
What are you going to do to help with the primer pocket from getting to big over time?
 
1mechanic said:
If this is true what causes case head separation?

If the brass doesn't flow forward from the belt area why does the brass get thin and separate just forward of the belt?

I love MagnumManiac's knowledge and experience, he is a wonderful help here on the forum but this is the one thing I think he has wrong.

On his 375 example there isn't much shoulder for pressure to act on to stretch the brass but in the 90's on a 264 win mag I have had case head separation and the brass was thinner just forward of the belt. I maybe ignorant to what caused it but I'm pretty sure it was the brass flowing forward from the belt area.
Click to expand...
You want proof that the case doesn't stretch UNLESS the handloader does it. Here it is, this case (ww-super) was fired 10 times with minimal sizing. Where is the stretching…
Case head separation has ONE CAUSE, no matter the case design, and that is EXCESSIVE HEADSPACE CAUSED BY BUMPING THE SHOULDER TOO MUCH.
 

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RD57 said:
By SAAMI standards you are correct. I'm not a commercial ammunition manufacturer and do not follow SAAMI specs 100%. I choose to headspace my belted mags on the shoulder just like my other bottleneck cartridges, I even load my 357 SIG ammo to headspace on the shoulder. I'm completely satisfied with my case life and accuracy resizing my brass this way.
Click to expand...
I am not and have not mentioned anything about the case after the first firing, only about the first firing and all the MYTHS about case stretching, it never happens…

Cheers.
 
Victor3Ranger1 said:
What are you going to do to help with the primer pocket from getting to big over time?
Click to expand...
There is a process that said to work in closing down the primer pockets. I haven't tried it yet. So I don't have any real experience as of yet. This what I have found out.
Need a stainless bolt long enough to reach the inside of the base, and small enough to go through the neck. You need a ball bearing about 1/2" in size. Will need to flatten 2 sides so it can be held in a vise. Place the case with the primer pocket over the ball bearing. Don't need a large hammer. Don't beat the crape out of it either. That will push the primer pocket back and tighten the pocket. Again I haven't tried it but will when I get going again.
 
Mike Matteson said:
There is a process that said to work in closing down the primer pockets. I haven't tried it yet. So I don't have any real experience as of yet. This what I have found out.
Need a stainless bolt long enough to reach the inside of the base, and small enough to go through the neck. You need a ball bearing about 1/2" in size. Will need to flatten 2 sides so it can be held in a vise. Place the case with the primer pocket over the ball bearing. Don't need a large hammer. Don't beat the crape out of it either. That will push the primer pocket back and tighten the pocket. Again I haven't tried it but will when I get going again.
Click to expand...
I would like to see this done just to know how
 
1mechanic said:
If this is true what causes case head separation?

If the brass doesn't flow forward from the belt area why does the brass get thin and separate just forward of the belt?
Click to expand...
You are correct but missing some data.
The main culprit step by step JIC:
The initial firing of the new case in the chamber is called "fire forming".
Resizing using directions from most die makers OVER-RESIZES most cases to assure the result will fit (any chamber) again.
Repeating this cycle causes separation, not just in belted cases but it is more prominent an issue with lets call it "Old Rules" chambers.
Minimize this way brass flows with neck and/or minimal body sizing.

The other way was outlined by Glen Zedicker, and there is a physically smaller symptom, a "doughnut" that forms in the case neck/shoulder area from repeated firing as well. The pressure wave from primer forward each firing causes both concerns. If you pick up his ammo book you'll see a mention of how some people interviewed anneal cases: "I stand em all up, I don't worry about the water, and tip the whole thing....into the trash" (not word for word but you get the idea). Which is great if you needn't be frugal.
 
Carey Farmer said:
Here is how I think about case stretching upon firing. I'm not sure I'm right about any of this, but this is what I think happens.

Upon firing, the firing pin forces the case to the front of the chamber. The front of the case is always softer than the rear of the case, so as the case pressures up, the case walls at the front of the case "grab" the cylinder walls first. Most length stretching of the case walls (to push the case head back to the bolt face) occurs at the rear of the case, because the front of the case walls have already "grabbed" the chamber walls. It's important to limit this stretching at the rear of the case, because that part of the case is work-hardened and won't stretch much before cracking.

In belted magnums, a new case headspaces off of the belt. So the firing pin can't force the case to the front of the chamber, and most stretching occurs in the front of the case, which has been heat treated to ensure ductility. Even 0.030" of stretch at the front of the case should be no problem.

Unfortunately, the SAAMI tolerance for the cartridge belt to case head distance is -0.008 ", so the maximum actual headspace between the case head and the bolt head could be as much as .010" or so, assuming the rifle was set up with .002" headspace against a SAAMI button.

When I build a belted rifle, I buy and dedicate 150 cases to the rifle, and I headspace the rifle using a sampling of those dedicated cases. Typically the bolt of a rifle headspaced that way fails to close on a SAMMI headspace button, suggesting that the case manufacturers I use don't manufacture their cases at the nominal (0.000" tolerance) SAAMI dimension. In any event, I'm confident that stretch at the rear of my cases upon first firing is 0.002" or less.

Also, I have my belted rifle reamers made up 0.010" shorter than SAAMI. That limits the stretch somewhat at the front of the case upon first firing, but more importantly allows subsequent sizings, headspaced at the shoulders, to go all the way down to the belt. I do have to lap 0.005" off the bottom of my sizing die to prevent bottoming on the shell holder though.
Click to expand...
Interesting on the reamer change! I was looking at Peterson Long cases in 300WM to use. I have a 7mm RM that I going have to reload for. You got me to thinking and did some hard looking at the two case make up. Sure is a different overall lenghts in the case. Interesting, I hadn't looked at that close yet until now. So I am going to reduce the powder charges and push the bullet into the lands to push the base to the bolt face to form the cases.
Sure got me to thinking. 'I know that won't get me to far".😁😂
 

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