Excessive head space???

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I have a 1904 Portuguese Mauser in 6.5x58 that I am in the process of reloading for. I wanted to ensure that the primer wouldn't be pierced when firing so I loaded a primer in my new brass and fired the primer only. When the primed casing was loaded in the firearm, the primer was flush with the head. After firing, the primer backed out (around a millimeter I would guess). Is this a symptom of excessive head space? Should I be worried? I am using virgin Winchester 8mm brass reformed into 6.5x58 with Winchester WLR primers. Any hazards to loading up a starting load?
 
Primers backing out is a sign of excessive pressure. It may also be a sign of bad headspace. Always check headspace with any milsurp.
 
On some rifles with very mild loads, primers can back out if there's enough headspace, too.
Sometimes, you can get primers that look "riveted" because they backed out before the pressure caught on and crushed them. Some people think it's because of excessive pressure but it is largely due to a combination of a generous headspace and/or new unstretched brass.
Best is to fireform using mild loads OR create a secondary shoulder by using a larger expander then resizing the neck partially to create a step. Try positioning that step on the neck so the action can just close then prime the case, put a small charge of fast pistol powder inside (W-231) and cap the brass with a ball of Parowax. Shooting that ball of wax will create enough pressure to fireform your brass with NO headspace whatsoever.
Just don't shoot it at anything you don't want to hurt because that small wax ball shoots out quite fast!:eek:
PP.
 
The pressure that builds up inside the primer cup when only a primer is fired will tend to push the primer back, and the case foreward. This can exaggerate headspace indications. The projection you are seeing could be a combination of both, plus perhaps a bit of excess headspace. You are forming your cases. Why not just size them so that the shoulder is slightly further foreward? If you can just feel the case when the bolt closes, you don't have to worry about the fit for the first firing. The cases will fireform, and if you are concerned, check them for any signs of incipient separation before reloading. Once the cases are fireformed, resize them to fit your rifle, rather than to some arbitrary standard based on the shellholder contacting the die.
Also, make sure than the case necks aren't too thick. 8mm to 6.5mm is a serious reduction.
 
perhaps try neck sizing your brass and running light loads
If the headspace is really excessive take it to a gunsmith at your earliest convenience.

Happy New Year
Nice Rifle

Wish I had one.
 
Well I fired a starting load (max load - 10%) and the gun didn't break and the case held up. I found that the exterior of the case had significant blackening on it. The primer held just like it should. The fired size was extremely close to the die-formed size. I do want to try neck sizing but will have to pick up a neck sizing die for 6.5. I do hope to find some lead 6.5 and work up a load for it as lead is easier on the barrel and brass, or so I find.

I would love to check head space, but finding Go/No-Go gauges for this caliber might be difficult?
 
brass doesn't stretch when fired with only a primer. it is to be expected that the primer will back out when fired with no powder since the cartridge is not being pressed against the bolt face.

and the blackening can be caused by too light a load, causing the neck not to seal the chamber properly.
 
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