Blew a Primer _ Analysis

[Pdvdh]

So I just weighed the case from the load fired 12/17/2017. 3.2gr more powder, 91fps additional velocity, more pressure, yet held its primer and the case web swelled much less. It weighs 257.5gr. Not one of the heaviest cases, and not much difference. So maybe the case weights aren't playing any role in stronger versus weaker case heads...

BTW, I also confirmed the bullet seating depths on the three remaining cases I prepared were not excessive. They were not jammed into the rifling. Bullet seating depth allowed a 0.010 jump to the lands.

 

[Pdvdh]

Does the hbn and uncoated bullet diameter measure the same?

They're all HBN coated now. I could strip the HBN in an acetone bath, but I doubt my 0.001" calipers are sufficient to provide a meaningful differential on the diameters.

Understand I'm visually interpolating between the 0.001 markings on the Mitutoyo dial caliper in order to resolve 0.0001" differences in my measurements.

 

[elkaholic]

I agree in theory of what Steve says about oversize bullets and undersize bores. We saw this with early 143 eldx bullets. Here is the problem with that
We,re you not using the exact same bullet combo when it performed without s problem at a 3.2 grain heavier charge? Could it be that a FEW of the bullets were. considerably over size?
I also see a red flag with the blown case being the lightest! If all of the missing weight was in the head, it could be a problem! I have also wondered if it is possible for a void to occur in a case head??

 

[Pdvdh]

My opinion is that if you are going to continue to use this bullet you should back off the throttle. They advertise this bullet as having the same pressure as conventional lead core bullets. That may be true in some rifles. Get rid of 100fps and I think your problem will go away.

My .02

Steve

Thanks Steve,
I really have no accurate means of measuring down to the 0.0001". The barrel is a Krieger 4-groove, 9.5 twist. I think Krieger advertises 0.308" groove diameter and 0.300" land diameter.

The conundrum is, again: Unless the manufacturing tolerance on the two bullets I fired was substantially different, then the same basic bullet yielded two pretty different pressures, in the reverse direction anticipated based on measured case web swell and MV.

I measured a number of bullets with my calipers. All measured the same, to the limitation of my calipers and eyes. I do have good vision...

I have shot this brand bullet in two other rifles (.284 and .338 calibers) enough to be getting a warm fuzzy feeling, with respect to accuracy potential. But in this rifle, only two shots fired thus far due to the resultant elevated pressure indicated on both shots.

 

[RockyMtnMT]

Thanks Steve,
I really have no accurate means of measuring down to the 0.0001". The barrel is a Krieger 4-groove, 9.5 twist. I think Krieger advertises 0.308" groove diameter and 0.300" land diameter.

The conundrum is, again: Unless the manufacturing tolerance on the two bullets I fired was substantially different, then the same basic bullet yielded two pretty different pressures, in the reverse direction anticipated based on measured case web swell and MV.

I measured a number of bullets with my calipers. All measured the same, to the limitation of my calipers and eyes. I do have good vision...

I have shot this brand bullet in two other rifles (.284 and .338 calibers) enough to be getting a warm fuzzy feeling, with respect to accuracy potential. But in this rifle, only two shots fired thus far due to the resultant elevated pressure indicated on both shots.

I can not disagree with you in this matter. I think there is a possibility that you are close to top end pressure with this mono bullet. My first gut thought with your op was a simple brass problem and just move on. Safe bet now would be to load a sufficient number of shots at a reduced load and see if you have another spike in pressure. I don't think you will, but there is only one way to find out. I don't think you are in dangerous territory, but I know you are not happy about popping a primer. Im thinking the ball is in your court now.

Steve

 

[can1010]

I wonder if their is a hardness issue with the copper they said on web site it was red copped. these mushroom like barnes where hammers break off. I will run the 128 .277s this weekend and compare to my known load with 126 hammer bullets. all mine measured .308 and .277 but my calipers wont do .0001 maybe if Steve is interested I can send him some .270 and .308 to check out

 

[elkaholic]

Pure copper definitely builds more pressure all else rqual.

 

[Pdvdh]

I'm thinking the ball is in your court now.

Steve

True yesterday, true today, true tomorrow. And that's what I was thinking when Edd expressed opinion about cartridge operating pressures. I'm the one combining the witches' brew of explosive materials into a nice shiny neat container and setting them off. Doesn't make much difference the cartridge. Not like a lamb being led to slaughter. Each rifle is different. Each cartridge loaded different. I control the outcome of the witches' brew I feed into my rifle. Poof! No eyebrows due to excessive pressures - my fault.

I've only fired two bullets in my 30/375 S.I., and I still have my eyelids and eyebrows. Sacrificed one Hornady casing, perhaps a defective one at that. Not too bad...

I'd like to know why the difference - the lower pressure & MV load loses its primer. The higher pressure & MV case head survives to be reloaded another day.

Would be nice to send these two casings into ADG, Lapua, Peterson, Lake City, Federal, or another case manufacturer with the ability to test brass case head strength. But there's nothing in it for them other than ugly, so why bother. That would be the next, most logical step. But only if the option was available at a VERY low cost. Because I'm cheap.

 

[elkaholic]

I'll ask ADG if they would be willing/able to do that. Not a bad idea.

 

[RockyMtnMT]

I wonder if their is a hardness issue with the copper they said on web site it was red copped. these mushroom like barnes where hammers break off. I will run the 128 .277s this weekend and compare to my known load with 126 hammer bullets. all mine measured .308 and .277 but my calipers wont do .0001 maybe if Steve is interested I can send him some .270 and .308 to check out

Red copper is a slang term for copper. More than likely c110 alloy. It is the cheapest and easiest to get. It is too hard for our liking.

Steve

 

[Pdvdh]

I had looked briefly at the 8x68S brass 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.

Rich,
I'm going to measure the distance the BAT extractor projects inward from the rim of the bolt head recess. It may be enough to fully engage the rim of the 8x68S RWS brass. It's spring loaded. If it projects in far enough to bottom in the extractor cut behind the rim of the case, we should really have very little concern as to the reliability of fired case extraction.

You could do the same, as you've got both the RWS casing and the BAT bolt face.

In other words, if the BAT extractor projects 0.010" further than necessary to fully bottom out in the Hornady 375 Ruger extractor recess just ahead of the case rim, then the BAT extractor will also fully engage the extractor recess in the 8x68S RWS case extractor slot.

 

[elkaholic]

Red copper is a slang term for copper. More than likely c110 alloy. It is the cheapest and easiest to get. It is too hard for our liking.

Steve

Another dead end but an elimination I guess.

 

[WildRose]

The ID of the primer pocket measures ~0.215", compared to a fresh primer pocket ID of ~0.208-0.209". The plunger mark where the case head flowed into the plunger recess on the bolt face is located between the A and D, of HORNADY.

No gas cutting evident around the perimeter of the primer pocket.
View attachment 88592
The primer was intact, found on the magazine follower after the case was extracted. The OD of the fired primer measures ~0.212", or ~0.003" smaller than the primer pocket. Again, no pierced primer and no pin-point torching visible around he perimeter of the fired primer. No primer face swell into the firing pin recess of the bolt face, but there's really very little slop between the firing pin and the hole in the bolt face on a BAT action.
View attachment 88593

If I'm not mistaken it looks like there is some scoring on the primer hole indicative of high pressure jet/heat. Do you see any on the primer itself?

What is the diameter of the primer compared to the others in the same box? An undersized primer could produce the same problem as an oversized primer pocket. Obviously not all primer pockets are going to be perfectly uniform in size, particularly those that are punched vs those that are drilled and primers are stamped rather than drilled so they too will tend to have some eccentricities.

 

[WildRose]

I remeasured the length of the fired casing. It was good, not long enough to pinch the seated bullet the chamber.

When I received my first two boxes of Hornady 375 Ruger cases, I weighed all 50 from one of the two 50ct boxes. The average weight of the 50 cases was 258.1gr. The lightest case weighed 256.3gr. The heaviest case weighed 259.9gr.

The case that lost its primer weighs 256.7gr. Only two of the 50 cases I weighed were lighter than 256.7gr. One at 256.3gr and one at 256.5gr. This raises my eyebrows a bit. If the lesser amount of brass is all missing at the web or case head, maybe the case was weakened at that critical location? What are the odds that of all 50 cases, the one that blew the primer is the third lightest case in the box, meaning that during manufacture it ended up with less brass than 47 of the other casings in the box of 50? Happenstance coincidence? I dunno...

Why don't you measure total bearing surface length and compare it to that of the bullets RM is shooting. Copper bullets will be 10-12% longer than traditional cup/core bullets of the same diameter and weight so I'm wondering if even with the grooves you may have more total bearing surface than he does which could affect peak pressures with otherwise identical loads.