What happened to this 300Win Mag Brass??

[Fire1]

The two pieces of brass in the picture are from a 300 Win Mag load I shot today: 165gr Nosler Accubond, 78.5gr IMR 7828, Winchester LRM primer, LOA 3.39. This should be a mid-range load according to my Nosler book. Although, the book claimed this would go about 3110 FPS, and my Chrony clocked it at an average of 3207fps for the four rounds I shot before I stopped. Clearly I have a case separation issue (I overworked the brass and had separations on four different loads), but what happened to the body of the case just below the shoulder?? What would cause it to form dents like that?

 

[mjyeagle]

what brand and how old?

 

[Fire1]

Remington Brass. I'm not 100% sure of the age, but I think this was only the 3rd loading.

 

[meadmkr]

I'd never seen this post-firing; only from having too much lube on the casing during resizing.... Is the camber clean/dry of oil/grease?

Its not a fluted chamber by any chance?

Keep up informed as to what 'ya find out!

 

[Fire1]

Yes, the chamber was dry and clean. It's not a fluted chamer. The rifle is a new Winchester M70. This only happened to two pieces of brass, out of the 10 shots I took today before I came home to pull the rest of my loads. Also I would think if the brass looked likethat prior to firing, then it would be straightened back out when fired. These brass were all throughly inspected and trimmed before I loaded them

 

[rcmodel]

Slow burning powder didn't expand and seal the case to the chamber wall before pressure got between it and the chamber. The pressure blew dents in the case before chamber pressure could stop it.

Up the powder charge, or use a slightly faster powder.

You might also want to measure your expander button.
Make sure it is at least .002" smaller then .308 bullets.
That will insure enough case neck tension to give sufficient bullet pull to get a good burn started. You could also try crimping the bullet to increase chamber pressure before bullet release.

If it is too big, chuck it in a drill and worry it down with emery paper to .306" or so.


The case seperations are the result of trying to headspace off the belt.
Forget it is a belted caliber and adjust your sizing die to headspace off the shoulder.

You want a very slight crush fit on the shoulder when you close the bolt on a sized case. Just enough you can feel it when you close the bolt.

If you just screw the die in and FL size, you are pushing the shoulder back too far and the case will stretch every shot until it breaks just like yours did.

rc

 

[Captcurt]

Too much freebore.

According to my "old" Speer Loading Manual #9, a rifle with too much freebore can have this problem. You can probably cure this by going to a faster burning powder.

 

[OYE]

"Remington Brass. I'm not 100% sure of the age, but I think this was only the 3rd loading. "

I take it that you are not using reloading labels and keeping track of how many firings.
I think you'll find it of much benefit on any of the Mag. calibers to keep very close records on your brass with rigorous inspections. Case head separations (even one) certainly aren't going to improve the smoothness of your chamber. The lifespan of your barrel may end up being much shorter than you might think.

Yes, Speer does show examples of shoulder collapse in # 10 as well
in Magnum calibers with too much freebore combined with slow burning
powders. They suggest a different powder "may" prevent a recurrence.
If a new gun you may wish to talk to Winchester about this if it's happening on cases that aren't separated. Good Luck

 

[Captcurt]

More stuff.

By the look of the heads of the brass above the web you are getting incipient head seperation too. I bet that you are full lenght resizing. The belted magnums headspace on the belt. If the chamber is a little long the brass will flow forward when you fire. Then when you resize full lenght the brass gets thin in front of the web. I had a 220 swift that I could load three times and it did the same thing. Try backing you resizing die out until cartridge shoulder barely touches the die. (Smoke it). This way you aren't working the brass any more than you have to.

 

[Fire1]

Thanks for the feedback everyone. I'm pretty sure the whole thing was caused be me excessively resizing the brass. Yes, I am full length sizing these. I shot this same load a week ago and had none of these problems. My plan is to first cull all of my old brass. I have a bunch from when I was working up loads from my first 300 Win Mag. I will use some new brass that I have and try this load again. I also have a load with 4350 that shows some promise, so that might be a better direction to go in as well. Then, I am going to either neck size or back the FL die off so I am just barely bumping the shoulder back. I had it adjusted according the to directions - touching the shell holder plus another quarter turn or so. And then I will do a better job of tracking my brass and how many loadings it has. This has been a learning experience. I've been reloading for over 20 years and never had any of these problems, even with my other 300 Win Mag.

 

[R.Clem]

Having shot the barrel out of a .300 WM in a Browning A-bolt, I learned quickly that all chambers are not created equal, my method was to simply neck size with a minimal amount of lube. Also lube the inside of the neck or get a carbide expansion ball. There will come a point where you will have to full length resize, screw the die in till you get enough sizing to chamber the case and no more. The belts will also grow in length and make chambering tough. You can turn a few thousands from front of the belt and get a few more loadings, but it isn't really worth the effort. If you have more than one .300 WM you may find that the cases from one won't fit into the other, a friend of mine couldn't chamber my handloads in his .300 WM, my cases were 5 thousands longer than his chamber.
This doesn't just apply to .300 WM, all cases are the same because they all grow under firing pressures. Full length resizing moves the shoulder back if the die isn't adjusted exactly right, then they grow to fill the chamber when fired, working the brass with every shot and loading.

Ray

 

[woods]

Case head separation. The dents on the case body at the shoulder junction theoretically occur when the gases escape out the separation close to the case head and try to exit forward out the bore




Belted magnums have a lot of space between the shoulders on new brass and the chamber. Take for example this Winchester Model 70 post 64 rifle firing factory ammo

shoulder position before firing


shoulder position after firing


that is .038" or so of a gap. However it headspaced on the belt and it only had .007" of headspace on that brass.

So the point is that you can get a lot of thinning and the start of a case head separation before you can prevent it. Unless you form a false shoulder by necking up and partial necking down but that is a real PITA.