6.5 x 55 case head separation - Graybeard Outdoors
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post #1 of 24 (permalink) Old 12-22-2019, 12:09 AM Thread Starter
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Default 6.5 x 55 case head separation

I had a couple of 6.5 x 55 case head partial separations with new Lapua brass and moderate handloads shot in a VZ24 with a new Brownells barrel. The rest of the cases show slight radial stretching/ring at the end of the web. Bent wire interior scratch tests are ambiguous...it catches on some cases but not others.

I pulled the headspaced barrel to drill and tap the front ring for scope base. It was not super tight and I retorqued it firmly. The bolt closes with barely noticeable resistance on the GO gauge. The Clymer GO gauge does not exceed the long dimension in my Lyman case length gauge.

Once fired Lapua brass exceeds the long dimension of the Lyman case length gauge regardless of the load. New Lapua brass, same batch, does not exceed the long dimension. I checked the brass from the starting load for a ladder load series and that case had stretched beyond the long dimension of the case length gauge.

I cannot find the test cases provided by the 'smith who set the headspace on the barrel but do not recall there being any indications of case stretching.

At first I thought the rear chamber diameter might be a bit too large, but would that account for the obvious case length increase? Bolt lugs don't show setback and I did not shoot hot loads. Did I get some debris between the end of the barrel shank and the receiver shoulders? The barrel shoulder appears to be seated on the end of the receiver.

I would appreciate any thoughts on case stretching problem before I ruin any more brass and ask the gunsmith to set the barrel back a bit.

Last edited by M134 Troll; 12-22-2019 at 12:12 AM. Reason: add
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post #2 of 24 (permalink) Old 12-22-2019, 01:31 AM
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Probably a headspace issue causing case to stretch. All chambers are not bored the same in that chambering, so I have recently read somewhere.
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post #3 of 24 (permalink) Old 12-22-2019, 01:22 PM
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It pretty much sounds like it has to be one of two problems. Either the chamber is over spec. for headspace or your bolt is setting back from the breech thrust when fired.
On a bolt action you should be able to take a fired case and put it back in the gun and close the bolt without a lot of effort.
I would bet you can't do that with your rifle.

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post #4 of 24 (permalink) Old 12-22-2019, 10:05 PM Thread Starter
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Yes, there is a lot of variability in Swede chamber dimensions, but I'm using new brass which has not been shot in another rifle and which has not been full length resized.

I'll see if a fired case rechambers.
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post #5 of 24 (permalink) Old 12-22-2019, 11:04 PM Thread Starter
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All fired Lapua cases rechamber.
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post #6 of 24 (permalink) Old 12-23-2019, 05:18 PM
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Now I would see if those same fired cases fit the cartridge gauge.
The only way I can see a case head separation happen is to have severe headspace ?

You could try priming a new or resized case and firing it and see if the primer is protruding out past flush with the end of the case.

I have had brand new Norma brand brass that would not chamber without being resized. So all new brass isn't always correctly sized either.

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post #7 of 24 (permalink) Old 12-24-2019, 08:58 PM Thread Starter
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Lapua cases fired in the Brownells barrel drop all the way into the case length gauge. Identical load fired in a M70 6.5 x 55 did not show web expansion ring. Identical load fired in another VZ 24 with unknown 6.5 x 55 takeoff barrel (mounted by the same shop which did the Brownells barrel but maybe 30 years ago) had some web expansion but would not drop all the way into the case length gauge.

I'll try some primer only shots as Jedman suggests. This might shine light on the oversized chamber theory.

Case length gauge fit suggests the Lapua brass is correctly sized. Will also smoke/mark shoulder of new brass to assure it is seating on the should of the length gauge. I recall having some domestic 6.5 x 55 brass which had undersized .473 case head size and which showed web expansion...but understandable given the head and base dimension.
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post #8 of 24 (permalink) Old 12-25-2019, 10:53 AM
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The first thing I would do, and I've done it before, is seat a bullet at the lands and the case base on the bolt breach, and fire it using a mid size load. If that case then chambers in the rifle, neck size it, reload it with its normal charge & jump, and fire it again. For all practical purposes You now have a chamber cast of Your rifle. Don't worry about spring back, this is close enough for what You want to know. The only gauge I care about is the chamber of the rifle. This spent case can now be measured in all its dimensions for die settings, etc. In Your case, Im willing to bet this spent case will not fit in Your gauge. Case base separation almost always means excessive head space. A rifle chamber, reloading dies, and case gauges, separately manufactured, have too much potential for tolerance stacking to have any value for Me. This spent case is what I go by.

Serious target shooters start with a chamber reamer, fire cases in the finished rifle, send them off to have custom dies made, and custom chamber gauge if desired. Now You have something. Not a collection of so called SAMMI components with their range of tolerances that could easily be incompatible.

The method I suggested can get You where You need to be...Good Luck 🙂

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post #9 of 24 (permalink) Old 12-28-2019, 10:14 PM Thread Starter
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Quote:
Originally Posted by jedman View Post
Now I would see if those same fired cases fit the cartridge gauge.
The only way I can see a case head separation happen is to have severe headspace ?

You could try priming a new or resized case and firing it and see if the primer is protruding out past flush with the end of the case.

I have had brand new Norma brand brass that would not chamber without being resized. So all new brass isn't always correctly sized either.

jedman
Primed a couple of new Lapua cases and fired them. Detectable primer protrusion resulted. Clymer No Go gauge is on the way from Brownells.
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post #10 of 24 (permalink) Old 12-28-2019, 10:23 PM Thread Starter
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All the Lapua cases, even the ones with head separation, fired in the Brownells barrel will slip all the way into the case length gauge whether they are neck sized or not.

Lapua cases fired in a M 70 push feed also fit in the case length gauge but ones fired in an older barrel of unknown origin on another VZ24 will not due to radial case expansion in the rear quarter of the case.
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