300 Winchester Mag stretching above the belt

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IMtheNRA

New member
I recently started to reload 300 Win Mag and I saw stretching right above the belt even on once-fired brass.

If I ever saw this shiny ring on my .223 or .308 brass, I'd discard the brass immediately. However, I've been told this is normal for belted brass and is not necessarily a sign of impending case head separation. Does this sound right?
 
Stick a bore scope down the case and take a look.

If you don't have a bore scope, use something pointed (a bent paper clip for instance) and feel around where the ring is on the inside.

If you feel something, you prolly oughta discard the case and find out why the case is stretching that much with one firing.

Another approach would be to saw the case from head to mouth into two halves and examine it.

You should size the case so that it does not support on the belt, but on the case shoulder.
 
That stretching mainly means your headspace (distance from the breech face to the recess the belt stops on) is long for the case. If the belt on the case is a much shorter distance from the head than that headspace measurement (and it often is), the case will stretch that whole distance. The only workaround I know is to fireform the case shoulders forward with a lighter load or a cereal load and then size it to headspace on the shoulder instead of the belt, thereafter.
 
I resized the once fired cases to headspace on the shoulder, using the Wilson gauge to set up my sizing die. So now, the case shouldn't stretch anymore than any non-belted rifle case, right?

If that's correct, then should I be worried about that initial stretch? I'll cut a few open to see if the case wall was compromised.
 
I resized the once fired cases to headspace on the shoulder,
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That's correct handloading procedure for belted cases after first firing.* (If you're hunting dangerous game, be SURE to cycle-test the rounds through action before heading into the field.)
I'll cut a few open to see if the case wall was compromised.
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Not req'd. Just straighten out a paperclip, bend a small "L'" at one end; sharpen/file to a point; and run it down into the case.

Any case-wall stretching/thinning will be quickly apparent.



* for case headspace dimensional set-up, I always recommend Hornady's comparator. Too many other factors come into play w/ a whole-case gauge like a Wilson's
 
Can you use a case comparitor fo see how much a fired case has stretched compared to an unfired case?

It isn't uncommon to see 0.02" of additional length. I shoot a lot of .300wm and while they do expand significantly after the 1st firing, I have not noticed the shiny pressure ring, or failed a paper clip test after 1 firing .

Factory new .300wm brass headspaces off the belt and the shoulder is well behind the chamber wall. After firing the case stretches to fill the chamber . If you size the case back down to near factory new, the brass will again stretch a lot and shortly you may have casehead separation. But, typically this is something you would see after a at least being sized and fired again (fired twice total).

If in fact you have a problem you likely either have weak brass near the pressure ring, or an overly large chamber. I have 3 different. 300wm's with brass being discarded after 7 firings due to enlarged primer pockets and not had indications of pressure ring stress. I try and size back to 0.002" clearance to avoid over working the brass. But it does grow after the first firing from 0.015-0.020".

You could also cut a case in half lengthwise and carefully examine it also. If it isn't growing outside the norms, it could just be a bad batch of brass
 
Resizing

If you're full length sizing, that is a mistake on cases that have only been fired in your rifle. I size mine so that the case will chamber and the bolt will close without much effort. I usually put the width of a penny between the die and shell holder.
 
Incipient Head Separation

Incipient Head Separation: For a time back in the dark ages this topic appeared fairly often in print. Sources agreed on the cause. If was due to a minimum chamber in the magnums plus maximum size FL dies ..:eek: It was enough of a problem for head separation. Not sure about all this but that's the way it was.:confused: Only ran into one person who actually claimed this die/chamber event. Check the case with the wire-already suggested. Neck sizing should be a cure-also already suggested. Magnum cases behave like rimed cases due to belt.
 
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Stats Shooter said:
…I have not noticed the shiny pressure ring, or failed a paper clip test after 1 firing.
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That's why I suggested his rifle's headspace may be long. He's seeing it after just one firing. However, Mr. Terry's post reminded me that I hadn't thought to ask if IMtheNRA sees the ring before resizing? The resizing die will often leave a brighter scuff mark at the pressure ring where the resizing stops and the brass is thicker and not diametrically expanded below it. That scuff mark is not an indicator of incipient head separation, as it happens well before the brass gets thin enough to be a concern.
 
Taking a bit of a side track, its seems that these issue crop up on a regular basis with belted cases (which are not needed)

Good news is there are lots of non belted choices.
 
I feel this is a problem and agree not acceptable for brass the OP plans to reload. The factory chamber seems to have a shoulder near or over the max side of spec. Head space is on the belt, so; i tmay not be technically accurate o say head space is excessive. Chamber length to shoulder is excessively long. Tricks sizing new brass may work. I never had to try this. It is the down side of the 300 WM. I know its a popular "black rifle" round. Too bad.

Perhaps a new match grade barrel?

I may have missed it. Did anyone mention sectioning the fired brass to confirm the stretching? If no, then that seems like the first step here.

Good news is there are lots of non belted choices.
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Yes, but; that would require leaving the BLACK side.
 
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I may have missed it. Did anyone mention sectioning the fired brass to confirm the stretching? If no, then that seems like the first step here.
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I would suggest measuring before and again after. That would be before firing and again after firing; after firing there is after sizing.

Manufacturers of components do not sell cases to reloaders that know what they are doing. In the perfect world the reloader would determine the difference in clearance between the belt on the case and forward movement in the chamber. We are not talking about forward movement of the case shoulder to the shoulder of the chamber.

This goes back to me saying reloaders struggle with the sequence of events between pulling the trigger and the bullet getting past the rifling. Reloaders assume the shoulder of the case moves forward on an belted case when fired; I always ask, how is that possible if the belt has the case pinned to the rear? That leaves tow options, one being the shoulder does not move forward but becomes part of the case body, the shoulder on the new case is a newly formed case.

The second option involves the case forming to the chamber; because of the confusion on the part of the relaoder he is lead to believe the case body, shoulder and neck moves as a unit. If that happens there is no other option but to stretch the case between the case head and case body.

And now we go back to the firing pin striking the primer before any of the events mentioned above happened: There are two events, one the firing pin strikes the primer, the next is the primer busting off. With pressure being the same in all directions the primer is pushed back and the case is driven forward. If time is a factor the firing pin strike and the primer busting off can create clearance between the case head and bolt face. That dies not seem like much of a problem but when the powder kicks off pressure inside of the case causes the case to lock onto the chamber. Once the case locks onto the chamber the case stretched. The area of stretch is limited by the clearance between the case head and bolt face. With the case locked onto the chamber the case stretches between the case head and case body.

I would like to have cases that had the ability to off set clearance between the bolt face and case head. I would like to have less head space on belted chambers.

With the belted system there is an inherent problem. The case expands in front of the belt. I do not shoot heavy/max loads because of this problem. When the case stretches between the case head and case body the case head is driven back; when the case head is driven back the area of the case in front of the belt is not supported. I have found cases with .018" expansion in front of
the belt.

F. Guffey
 
Last time I checked if you turn mag die over there place for the belt and headspace is above that in the die. there is nothing in die to stop shoulders from moving forward except the shoulders.

You have to get reamer print find out +/- to shoulder length and above belt. All you have to do is take expander out look in die. I can drop new case in die and slip shell holder on make sure belt against rim in the die.
 
You have to get reamer print find out +/- to shoulder length and above belt. All you have to do is take expander out look in die. I can drop new case in die and slip shell holder on make sure belt against rim in the die.
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You have to get reamer print
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I measure the length of the chamber from the shoulder to the bolt face, I measure head space on belted chambers. I have no problem cutting/grinding the belt off, I modify head space gages from go to infinity, that is one gage.

F. Guffey

I have one 300 Win Mag rifle, it shoots one hole groups, the shoulder makes contact with the shoulder of the chamber at the sesame time the belt head spaces in the chamber.
 
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