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Old October 25, 2012, 05:18 AM   #1
Join Date: March 10, 2012
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Fire Forming in a Martini action


I just fire formed a box of .22 Hornets into the K-Hornet in a re-barrelled bsa martini for the 1st time ever.

I have noticed that the cases width expanded only on one side. It is quite prominent just forward of the cases head.

With my limited knowledge, I am guessing the case is not being centered when loaded and is laying on one side of the receiver. My next assumption is that the case has now been overstretched on the one side and is a prime suspect for early head separation.

Can anyone shed some light on this.

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Old October 25, 2012, 06:56 AM   #2
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Some pics would be very helpful. If your cases are stretched only on one side you have a severely mis-shapen chamber, unknown cause, and you're due for a re-barrel job. GW
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Old October 25, 2012, 08:24 AM   #3
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AFAIK, the only difference between a standard Hornet and a K-Hornet is in the blown out shoulder area, so if your case is expanded near the head/rim, as if it fired while lying in the bottom of an oversized chamber, it most likely was...............

I would think something's up with the chamber proper, to make it larger than a standard Hornet chamber, allowing the expansion, or the cases were excessively sized down prior to the fireforming (which could amount to the same thing, relatively).

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Old October 25, 2012, 07:01 PM   #4
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Goatwhisker, I tried to photo it yesterday but it didn't come out any good. I'll try again using another camera.

PetahW, the cases fire formed were brand new Winchester hornet. The neck appears to have formed ok.
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Old October 26, 2012, 08:43 AM   #5
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I think this thread belongs in handloading, as there isn't necessarily a gunsmithing issue involved, so I'll move it for you.

Winchester sometimes has pretty awful wall thickness variability and the thin side will expand more than the thick side; what the late Roger Johnston called a banana shaped case from the slight longitudinal curvature that often also results. Unless you get a NECO gauge or the RCBS Case Master, both of which use the chord anvil Roger Johnston designed for the NECO gauge originally (I think the patent expired, which is why RCBS now has it), I don't know a good way to see wall thickness runout back near the case head. But that's what you want to measure.

Unless you know your chamber is oval, the brass wall thickness seems like the most likely critter.
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martini k hornet

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