What happened…pierced primer???

[Lonewolf74]

So the other week I was doing some load work up with my 338 Norma improved. I had been shooting it for a while at 92 grains of H1000 with a 285 ELDM, so I started there and went up in one grain increments to find the ceiling and where pressure signs started.

So I had 92, 93, 94 and 95 grains of H1000 under a 285 ELDM seated .020 off the lands, Peterson 338 Norma brass. The first thing I noticed was a pretty good velocity jump from 2860 at 92 grains to 2940 at 93 grains. The rest of the velocity gains were more average and expected with 94 grains at 2975 and 95 grains at 3000. The 95 grains load had ever so slightly heavier bolt lift so I know this is the upper limit.

I shoot my load work up in a round robin fashion and everything was proceeding as anticipated until the 3rd shot of the 93 grain load. Upon inspection of the case I find a very flattened and pierced primer.

I've never experienced a pierced primer or even a very flat primer before and I'm not sure what to make of it? Velocity for that exact shot was 2934 and it grouped perfectly with the first 2 and no increase in bolt lift. Just a flat, pierced primer and some extra gun smoke odor.

So all that to ask what are some possible causes for this? I am using Federal 215M primers in this load.

 

[Lonewolf74]

Picture of the cases top row 92 grains second row 93 grains third row 94 grains fourth row 95 grains. The rifle has dual plungers and leaves the ejector marks at low pressures so I do consider them but discount them till they start showing more clear as seen in the last row.

 

[Zen Archery]

Bad charge? Jammed into lands or case?

 

[Dean2]

Not sure if you have those cases in the order of firing from left to right, but the far left cases have nice rounded edges in the primers. All primers show a bit of cratering so you have an over size firing pin hole. This will allow a primer to pierce easier but the crater is also being flattened back out as the case head pressure goes up and the primers flatten.. As you move to the right. the primers get progressively flatter on all loads. If they are left to right in the order they were fired I would say that the heat build up in the chamber is upping the pressure in each of the loads.

The case that pierced shows higher pressure than the others. Flattened and pierced primer, as well as more pronounced ejector marks. You either got more powder in there than you though or the brass has a smaller internal capacity. I would fill it with water and compare it to the other brass water capacity. I would also not re-use that case.

 

[Lonewolf74]

What do you mean by bad charge?

If I had accidentally overcharged that particular case I would have expected to see a velocity increase but that shot actually had the lowest velocity of the 4 at 93 grains.

As far as having the bullet jammed I can't say it's impossible but is unlikely. I measure every single bullet to the ogive to make sure they are seated .020 off +- .0005. Even if I happened to miss one I've never had it be more then .002 off out of the seating die.

 

[Lonewolf74]

Dean2, checking the water capacity of that case is a great idea I didn't think of…and regardless of results I don't intend to shoot that case anymore

 

[Lonewolf74]

For clarification on the case order in the picture.

The cases are in order of how I shot them but it was not just left to right, top to bottom it was in round robin fashion.

So shot number 1 was top left case, shot number 2 was first case in second row, shot number 3 was first case in 3rd row etc.

I would take a full minute between each shot to minimize heat build up. I took a 10 minute break after the 9th shot, the pierced primer shot was the first shot taken after the break. It was 32 degrees out with a 10 mph wind. Cold enough to keep the barrel cool and fully cold after 10 minutes but I wouldn't think cold enough to make weird things happen.

I did not shoot the 4th shot of 95 grains because of having some sign of pressure and the group being scattered.

 

[Dean2]

Interesting then that the second round Robin shows higher pressures on ALL loads, based on the primers, than the first round does. I would check the throat for carbon ring as well as just how fouled the barrel is. Something is causing the pressure to rise the more rounds you fire. If it isn't heat, has to be something else.

Be very interested to hear if you ever figure it out. Best of luck.

 

[BillLarson]

View attachment 633574Picture of the cases top row 92 grains second row 93 grains third row 94 grains fourth row 95 grains. The rifle has dual plungers and leaves the ejector marks at low pressures so I do consider them but discount them till they start showing more clear as seen in the last row.

TOO HOT A LOAD....

 

[Dean2]

TOO HOT A LOAD....

Winner winner chicken dinner!!!!. Never even occurred to me to check the published load data because the loads he quoted are a long ways below the H-1000 powder charges for my 338-378. I presumed the OP knew what he was doing. Wrong big time.

Starting load is 7 grains over published max and velocity for a regular 338 Norma Mag, and at 92 grains is 200 fps over published velocity at 60,000 PSI. Going to 93, 94 and 95 and those velocities, is really asking for problems. No wonder you blanked a primer.

 

[lancetkenyon]

Winner winner chicken dinner!!!!. Never even occurred to me to check the published load data because the loads he quoted are a long ways below the H-1000 powder charges for my 338-378. I presumed the OP knew what he was doing. Wrong big time. Starting load is 7 grains over published max and velocity at 92 grains is 200 fps over published velocity at 60,000 PSI.

View attachment 633609

The OP's cartridge is a .338 NM Improved. Not sure if it is 33*, 35*, or 40*, but it is NOT the 338 NM chamber. So don't use .300NM load data as a reference for the Imp chamber.

Here is a .300NM (prior to fire forming) vs .300NMI 33* for reference. Big difference in case capacity. This particular rifle will push a 230 @ 3100 near max, and a 245 @ 2968 (not max).

 

[Dean2]

The OP's cartridge is a .338 NM Improved. Not sure if it is 33*, 35*, or 40*, but it is NOT the 338 NM chamber. So don't use .300NM load data as a reference for the Imp chamber.

Here is a .300NM (prior to fire forming) vs .300NMI 33* for reference. Big difference in case capacity. This particular rifle will push a 230 @ 3100 near max, and a 245 @ 2968 (not max).
View attachment 633617

I am well aware he is shooting an Improved. Typical velocity gain out of large AI improved cases is 100 to 200 FPS over the base cartridge. Trying to get 400 FPS more means you are way over pressure, even in a 40 degree improved case.

 

[lancetkenyon]

I am well aware he is shooting an Improved. Typical velocity gain out of large AI improved cases is 100 to 200 FPS over the base cartridge. Trying to get 400 FPS more means you are way over pressure, even in a 40 degree improved case.

I definitely don't disagree with this. Adding 10gr charge weight to that book max for the parent case is really pushing it too far.

I am seeing pressure signs on every case. 92.0 to 95.0gr.
2860fps with a 285 is very "impressive" to say the least unless he is shooting a 32" barrel.

 

[Greatgrandad]

I am seeing ejector swage marks on some of those cases, so pressure looks high on more than just the pierced primer case. Barreling fouling of various types can lead to pressure increases, and a case of slightly less capacity may also add to the pressures that already appear to be high.