Blew a Primer _ Analysis

[just country]

morning, was this a new federal case? if not how many
times has the case been reloaded? was the primer
oversized from reloading? just curious??
did the primer have a blow hole in the middle?? GBOT TUM

 

[can1010]

will the 8x68s brass be ok being .009 smaller at base. wont that let it expand to much loosing primer poctets

 

[elkaholic]

will the 8x68s brass be ok being .009 smaller at base. wont that let it expand to much loosing primer poctets

I and a client have both fire formed one and it extracted just fine. We still don't know for sure if there wijj be extraction issues but will be testing more full loads. I don't think it will affect the primer pocket, but we'll see....rich

 

[Pdvdh]

will the 8x68s brass be ok being .009 smaller at base. wont that let it expand to much loosing primer pockets?

I don't think that will cause any problems. It's no worse than the portion of the 375 Ruger case where it's unsupported by the steel chamber. Both cases are unsupported over the small length that protrudes from the steel chamber of the barrel. The brass case heads are designed tough enough in that area to hold together, even though unsupported by the steel chamber.

However the diameter of the rim of the 8x68S measures ~0.020" less than the 375 Ruger case rim. The 8x68S rim is rebated down to a smaller diameter than the web. 0.010" less radius. That's a mild concern. I'm hoping that loss of 0.010" rim radius will not cause unreliable extraction with my BAT extractor.

I see Rich responded. Hope this isn't a duplicate... I see I've added some additional explanation on case head strength in the unsupported butt end of the cartridge case...

 

[Oldcappj7]

Rich, I've still only fireformed the one 8x68mmS brass to 30/375SI however I am going to assume there will be fairly good consistency in the RWS cases. The primer felt good pressing out and the pocket measured exactly the same as virgin brass. I don't know exactly the brass flow on forming these but it didn't measure like it was moving any from the backside, more likely pulling back from the neck end which shrunk back about .024.

 

[elkaholic]

Rich, I've still only fireformed the one 8x68mmS brass to 30/375SI however I am going to assume there will be fairly good consistency in the RWS cases. The primer felt good pressing out and the pocket measured
exactly the same as virgin brass. I don't know exactly the brass flow on forming these but it didn't measure like it was moving any from the backside, more likely pulling back from the neck end which shrunk back about .024.

Thanks Jace and thank you for starting this useful work and informing me......rich

 

[Oldcappj7]

Blind pig.....acorn. I was looking for a replacement idea figuring there had to be something better than that Hornady brass and actually I was looking through reloading book ar cases about the same time Paul mentioned the 8x68mmS on a thread here back a bit. So I just figured it was worth the 40 bucks to know if it worked or not.

Glad to be a guinea pig

 

[elkaholic]

Blind pig.....acorn. I was looking for a replacement idea figuring there had to be something better than that Hornady brass and actually I was looking through reloading book ar cases about the same time Paul mentioned the 8x68mmS on a thread here back a bit. So I just figured it was worth the 40 bucks to know if it worked or not.

Glad to be a guinea pig

I had looked briefly at it once and I think I passed because of the .512" rim but it may not be a problem. That RWS brass is TOUGH and should really help this cartridge. I'll sell Edd some dies at cost and give him free reamer use and maybe he can do some pressure testing for us!

 

[Pdvdh]

And risk getting squib data from Edd? Bullets that won't clear the muzzle?
Better to charge him full rate!

 

[elkaholic]

And risk getting squib data from Edd? Bullets that won't clear the muzzle?
Better to charge him full rate!

I thought maybe if I threw out an olive branch, he would quit following me around like a yapping dog everytime I come up with a cartridge!
Seriously Edd; I really will stand behind my offer. Let me know if you are interested....rich

 

[dok7mm]

Phorwath, it seems the general consensus is soft or defective brass, for your problem. That makes sense to me, but I noted the bullets were HBN coated. I was wondering if you treated the bore with the slurry, prior to shooting that first bullet. Those of us that use the HBN, including you, know that we have to back off the initial charge weight for a few rounds to reduce pressure, when we've cleaned and retreated barrel. When I failed to remember to back off, I got a first shot that was 247 fps faster than my normal speed.

It was probably the brass, but I thought I would mention this, just in case. I hope you get it squared away.

 

[Pdvdh]

No, I didn't pre-treat my bore with a HBN / alcohol mixture. So that possibility can be dismissed.

The prior bullets fired in the barrel were the 225gr Hornady ELD-M bullets. I never cleaned the bore prior to firing these two monolithic copper bullets. All bullets were HBN coated.

 

[Pdvdh]

What if the primer let go first before full pressure developed, relieving gas through the relief holes in the action and into the bolt face and firing pin recess.
That might explain the loss of velocity.

The primer maintained it's structural integrity. The fired casing primer pocket ID is ~0.215". The fired primer OD is ~.211". So I don't think gas escaped until after the brass case head fully expanded, and even then maybe not until after the pressure peaked, and the primer contracted back down to 0.211" OD. I think at peak pressure, the primer was expanded tightly to the wall of the primer pocket, and after peak pressure passed, the brass primer pocket contacted down to 0.215" while the primer contracted even more, down to 0.211", allowing gas to escape.

Maybe there was an instantaneous, short-term pressure spike that blew the primer, yet didn't translate into higher MV, but I think not.

 

[Pdvdh]

morning, was this a new federal case? if not how many
times has the case been reloaded? was the primer
oversized from reloading? just curious??
did the primer have a blow hole in the middle?? GBOT TUM

The case was a Hornady 375 Ruger, not a Federal casing.
The case had been fired in order to fire-form it to conform to the larger dimensions of the "improved" chamber. The case web diameter was measured and recorded prior to firing this load, as I normally do during load workup. I monitor case web expansion after firing to help identify excessive chamber pressures when working up a new load. Neither the case web or the primer pocket were expanded/swelled prior to this firing.

No, the primer did not pierce thru its center. No gas escaped thru any hole, crevice, or defect in the primer.