Blew a Primer _ Analysis

[WildRose]

Nice. Yes, please let me know if you see any sign of soft case heads. I may be moving to the 8X68S RWS brass, but in the interim period, it'll be the Hornady 375 parent casings.

No problem at all.

Of the eighty or so I've already fired that were loaded factory ammo no problems but you never know how consistent any components are from one lot to the next till you try them.

I think you missed this one... .

https://www.longrangehunting.com/threads/blew-a-primer-_-analysis.197020/page-3#post-1389338

 

[Pdvdh]

Phorwath having shot a lot of RL26 in the 7mm STW, 300wm, 300 Rum and a few others with your case size and projectile weight it seems you should be within, or very close to safe pressures.

I am however unfamiliar with the bullet you are shooting so I wonder about bearing surface compared to say the Peregrines and Barnes TTSX. Do these have the same cannelure grooving or are they slab sided?

Sorry I missed this point and question.
These lathe turned monolithic copper bullets do have reliefs along the sidewalls in order to reduce the bearing surface. The Badlands Precision web site will show some photos. There are two relief cuts along the shank on this particular .308 bullet.

 

[WildRose]

Sorry I missed this point and question.
These lathe turned monolithic copper bullets do have reliefs along the sidewalls in order to reduce the bearing surface. The Badlands Precision web site will show some photos. There are two relief cuts along the shank on this particular bullet .308 bullet.

Ok, so that eliminates that.

Back to head scratching. ...

 

[Edd]

........I'll sell Edd some dies at cost and give him free reamer use and maybe he can do some pressure testing for us!

.................Seriously Edd; I really will stand behind my offer. Let me know if you are interested....rich

Ok, I'll take dies and a reamer for your short 338, the one that outperforms a 340 Weatherby and a 33 Nosler. Just kidding, I'm not interested, but I do like that cartridge.

A loosened primer, a swelled case web, a stuck bolt, or even a split barrel or receiver, might be shrugged off or attributed to poor quality or defective components. If someone gets injured, the Lawyers will help with the pressure testing.

 

[RockyMtnMT]

What is the dimensions of the bullet in relation to the the bore and groove?

Steve

 

[just country]

morning, the hen house bickering is not amusing. some of the long time
members have one time or the other had experiences of this sort.
the one item has come up numerous times is the brass! as we all
know is when fireforming cases there is vast amounts of pressure in the neck
case shoulder and rim of the case. the pressure of the ignition of the
primer, powder, pressures the case to expand in both directions. to me there
r 3 questions. Primer, burn rate of powder, and brass. now change the
primer, change the powder, change the bullet. not
all at once. the builder, and client have had the same problem.
this is a WILDCAT cartridge. 2 minds r better than 1. there is
a common dominator. Just me. GBOT TUM

 

[elkaholic]

Ok, I'll take dies and a reamer for your short 338, the one that outperforms a 340 Weatherby and a 33 Nosler. Just kidding, I'm not interested, but I do like that cartridge


A loosened primer, a swelled case web, a stuck bolt, or even a split barrel or receiver, might be shrugged off or
attributed to poor quality or defectiv

components. If someone gets injured, the Lawyers will help with the pressure testing.

Ok, I'll take dies and a reamer for your short 338, the one that outperforms a 340 Weatherby and a 33 Nosler. Just kidding, I'm not interested, but I do like that cartridge.

A loosened primer, a swelled case web, a stuck bolt, or even a split barrel or receiver, might be shrugged off or attributed to poor quality or defective components. If someone gets injured, the Lawyers will help with the pressure testing.

Edd...I want you to produce one quote for the .members you are trying to influence, that was made by me that states the 338ss will outperform the weatherby or
nosler. If and when you do that, start another thread and I will be happy to respond! Until then, I am through responding to anything you say. You have not offered Paul anything constructive, and it is apparent to all that you don't intend too. For whatever your reason is, your main interest seems to be trashing me.
Maybe you could get the attention you seem to crave if you developed something yourself!
Just s thought. DONE

 

[Pdvdh]

What is the dimensions of the bullet in relation to the the bore and groove?

Steve

Full diameter of the bearing surface measures ~0.3081 - 0.3082". I'm visually interpolating between the 0.001" divisions on my Mitutoyo dial calipers
The diameter at the two concave reliefs lathed out of the bearing surface measures ~0.2995".
Here's some pics of the bullet. The bullet in the foreground (in focus) is the one that was seated and then pulled in order to weigh the powder charge. The drag marks left by the case neck are visible on the bearing surface of the bullet. The ring to the right at the ogive on the bullet was caused by my RCBS collet style bullet pulling collet.

Seated and pulled bullet:

And an unseated, HBN coated bullet:

 

[tbrice23]

Does the hbn and uncoated bullet diameter measure the same?

 

[Pdvdh]

Repeated some measurements with my dial calipers this morning.

The web diameter of the casing (just forward of the rim) that lost the primer measured 0.5299" prior to firing. It now measures 0.5342" after firing, for a web expansion of 0.0043". Too much pressure for the web rule of thumb is considered to be ~0.0005", and that's when I usually back off the gas pedal.

I measured the rim diameter of this casing at ~0.5347". So the rim diameter is now larger than the web diameter (0.5342").
Next I measured the diameter of the web and rim on a casing that had only been fireformed, and never experienced full normal operating pressure. The web measured ~0.5308" and the rim measured ~0.5282". So the rim on the fresh case is 0.0026" smaller than the web.
On the other hand the rim on the blown primer case is larger than the web, by 0.0005". This means, all in all, the rim on the blown primer case expanded ~0.0017" more than the web expanded.

 

[Pdvdh]

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.

The primer was intact, found on the magazine follower after the case was extracted. The OD of the fired primer measures ~0.211", or ~0.004" 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.

 

[Pdvdh]

All in all, the pressures weren't extremely high, and I don't claim they were. Nothing like the Winkfish 300RUM casing in the other "How to blowup your rifle" Thread.

The puzzler here, the anomaly - is that the cartridge case loaded with 3.2gr less powder, 91fps less MV, fired in ambient temps 5F colder, enlarged the case web 0.0043" and lost its primer. While the cartridge casing loaded with 3.2gr more powder, firing the bullet with 91fps additional velocity, in 5F warmer temps, enlarged the case web only 0.0026" and held its primer.

That's why this Thread was started. And the most susceptible culprit is the differences in elastic yield strength of the case heads. One softer (less strong) than the other.

 

[RockyMtnMT]

I can't say for sure, but the copper bullet may play a role here. This bullet does not have a lot of relief in the baring surface to reduce pressure. Your measurement of the OD of the bullet is slightly over caliber in order to seal the bore. There is a .0005" +- tolerance in custom barrels. We hold a +- .0002" tolerance for our bullets, which is tight. Not sure what their tolerance is. Lets say it is as good as ours. If your bore is on the tight side of tolerance and the bullet was on the big side of tolerance, you could be close to .001" larger bullet dia than caliber. With a relatively large baring surface the engraving pressure will be high. With relatively little area for displaced copper to flow into after engraving also elevating pressure, you are dealing with the typical mono metal bullet problem.

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

 

[Pdvdh]

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