Interesting, the base to ogive measurement I get with the cartridge that drops free under its own weight is 2.1465". So perhaps it is correct.
Blown out primers and pressure signs
- Thread starter mikehill85
- Start date
Interesting, the base to ogive measurement I get with the cartridge that drops free under its own weight is 2.1465". So perhaps it is correct.
dellet
Gold $$ Contributor
Back to SAMMI
That is where the first hint of lands will start 2.140”, an be full height by 2.302”
Hodgdon lists that bullet at 2.800, to insure easy feeding from the magazine is the first assumption, but it’s less than max SAMMI. That can be a real good indicator that this bullet can not be loaded to max length. Might be worth checking that number.
That is where the first hint of lands will start 2.140”, an be full height by 2.302”
Hodgdon lists that bullet at 2.800, to insure easy feeding from the magazine is the first assumption, but it’s less than max SAMMI. That can be a real good indicator that this bullet can not be loaded to max length. Might be worth checking that number.
Yup, always my sharting point to find a max COAL with any new to me bullet.
Then I document that max COAL in my load notes for that particular rifle and never exceed it.
Not precise as bullet batch lots do vary but gets you in the ballpark to where you can start experimenting with bullet jump.
However in my sporters max COAL is always determined by mag length.
I borrowed a reamer to do my first barrel in this cartridge without studying all the goesintas and had to cut the tenon off and redo the chamber with a reamer I ordered with all the freebore ground off . This was so I could find a bullet to seat above the doughnut and stay at mag length . It seemed to me they just threw this out there with out understanding the triple reliance of brass build up , mag length , and optimal bullet jump for best accuracy . And yes when you start hard bullet jams combined with bullet shanks in the doughnut crowding your powder column strange things are going to happen . I have probably done 12 or barrels or so and set them all up for Berger or Sierra 130s' .
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Old Navy
Gold $$ Contributor
40.9 Grains of H4350 under your 147 is not close to a hot load.
Even the 140 Eld-m are below the neck shoulder junction if seated for short action chamber.
I have had a couple chambers you could not drop a bullet in a once fire case. ( 2 to 3 would)
I have cratered primers on a few rounds and then a clean burned hole in one on several guns.
The first time I went though all the steps you have. Having the firing pin bushed cured that Remington. I had the same problem on two Model 12 savages since. The last Savage I bought. I just sent it Carlsbad before even shooting it.
Even the 140 Eld-m are below the neck shoulder junction if seated for short action chamber.
I have had a couple chambers you could not drop a bullet in a once fire case. ( 2 to 3 would)
I have cratered primers on a few rounds and then a clean burned hole in one on several guns.
The first time I went though all the steps you have. Having the firing pin bushed cured that Remington. I had the same problem on two Model 12 savages since. The last Savage I bought. I just sent it Carlsbad before even shooting it.
I adjusted my die to push the shoulders of the brass back 0.002" and I adjusted the seating depth of the bullets to produce a COAL from my reloading manual. See brass from the shooting session. I was shooting N555 and worked up from 41.1 grains to 42.6 grains in 0.3 grain increments. I have labelled the powder charge of each column of 5 shots. I had a blown primer and pressure signs at 42.3 grains, seemingly at random.
Another interesting (though probably not meaningful) fact is that the brass with the blown out primers have significantly enlarged flash holes compared to normal brass.
Primer: Remington 9-1/2
Brass: Hornady LRP
Bullet: 147 grain Hornady ELD-M
Powder: N555
Charge: 41.1 - 42.6
CBTO: 2.1465
Another interesting (though probably not meaningful) fact is that the brass with the blown out primers have significantly enlarged flash holes compared to normal brass.
Primer: Remington 9-1/2
Brass: Hornady LRP
Bullet: 147 grain Hornady ELD-M
Powder: N555
Charge: 41.1 - 42.6
CBTO: 2.1465
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dellet
Gold $$ Contributor
Your CTBO is listed as the same as where you found contact with the lands. Then you pushed the shoulders back .002”.
That pushes the bullet forward and back into the lands.
It also moves the neck forward.
From your photo it looks like the brass is too long. There is a 45* angle that transitions from neck diameter to freebore. It looks like that is your trim length.
Under pressure the neck stretches with the bullet and pinches in the angled area. With the way you’ve sized and trimmed your brass it’s a potential problem.
Yes, I wrote that down incorrectly. The CBTO dimension was 2.1265.
I removed the photo because none of the other cases with blown primers had this feature.
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Did you have primers getting blown out of the primer pockets or were you just cratering or blanking primers?
In my case, it is definitely caused by high pressure, given how flattened the case heads are. I even had one where the case head expansion caused the extractor to fall out of the bolt face when I opened the bolt. I was able to put it back in and it was fine but it is definitely caused by pressure.
The thing is, if you look at the brass from yesterday's shooting session, there really were no signs of pressure on the brass at lower or higher charge weights than the one that was over pressure. Everything was fine and then, Bam!
jelenko
Gold $$ Contributor
Is there a mark on the case base at 11:30 - 12?
jelenko
Gold $$ Contributor
Are there ejector marks on any of the cases with no primers?
As someone else mentioned, ALL of the primers look just fine.
An idea: Measure the case capacity of the cases with missing primers and a few of the ones with primers still in.
The case with the blown primer has an ejector mark. The third from the bottom in the 41.7 grain column looks like it has an ejector mark in the photo but looking at it in person, it is hard to tell. It is likely a very light ejector mark, possibly from an earlier firing. The primer still has rounded edges on that piece of brass, so I don't think it saw significant pressure during this latest range session.
dellet
Gold $$ Contributor
Knowing your overall length would be helpful. There is no published data that lists CTBO for comparison. But here’s the bottom line.
Seeing photos of case mouths of other brass that popped primers could also be helpful.
Side note, how much are you having to trim between firings?
You have a chamber that’s on the tight side, your load is less than 1% off max. This is why start low and work up, is driven into peoples heads. It could be a tight bore, something outside our your control. At least you found and eliminated other problems.
The only thing that stands out right now is neck length.your’s is questionable. We know you pinch one neck, others might be doing the same thing but not as obvious.
If everything you can measure is the same or reasonably close to factory ammo, same bullet, same seated depth. And you keep having problems, the only thing that is different is powder/charge for the cartridge, and chamber and bore size of barrel.
At some point you just need to accept what thousands of hand loaders have found before. Book max and your max are rarely the same. From what I can see, your velocities are also higher than predicted, another indicator of higher pressure with lower charge weight.
Seeing photos of case mouths of other brass that popped primers could also be helpful.
Side note, how much are you having to trim between firings?
You have a chamber that’s on the tight side, your load is less than 1% off max. This is why start low and work up, is driven into peoples heads. It could be a tight bore, something outside our your control. At least you found and eliminated other problems.
The only thing that stands out right now is neck length.your’s is questionable. We know you pinch one neck, others might be doing the same thing but not as obvious.
If everything you can measure is the same or reasonably close to factory ammo, same bullet, same seated depth. And you keep having problems, the only thing that is different is powder/charge for the cartridge, and chamber and bore size of barrel.
At some point you just need to accept what thousands of hand loaders have found before. Book max and your max are rarely the same. From what I can see, your velocities are also higher than predicted, another indicator of higher pressure with lower charge weight.
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The COAL was 2.787".
I barely have to trim at all between firings, since I trim every time.
See attached photos of the neck of 6 other pieces of brass that had blown primers (these are borescope photos with the brass in the chamber). It turns out there was one more with a similar feature to the one that blew yesterday. I believe they are crimps. I had loaded some bullets with cannelures and crimped them. I would have thought these crimps would have gotten straightened/flattened out during the firing process, but maybe not. In fact, I think I can see marks from the cannelure in what I believe to be a crimp in IMG_7619.
Yes, I understand I might not be able to get to a certain manual's published max charge without pressure but a couple weeks ago I got a blown primer at 41.1 grains of N555. This past weekend I had no pressure signs whatsoever at 41.1 grains of N555 but blew a primer at 42.3 grains with no pressure signs leading up to it or even at a higher charge weight. I'm sure I can go low enough in powder charge that this doesn't happen anymore but it doesn't explain why it keeps randomly happening.
Attachments
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dellet
Gold $$ Contributor
A couple weeks ago you were jamming bullets deep into the lands.
All of the brass you have that was fired like that is suspect, possible loose primer pockets.
In the photos, there is a clean area ahead of the case. Possibly due to longer necks being fired before?
It would be interesting to see a photo of the same place without brass.
All of the brass you have that was fired like that is suspect, possible loose primer pockets.
In the photos, there is a clean area ahead of the case. Possibly due to longer necks being fired before?
It would be interesting to see a photo of the same place without brass.
Stop right there and send the rifle back to your smith and have him correct the chamber length. Factory ammo is normally a few thousandths short so it chambering does not surprise me.
It is true that the cases didn't drop free under their own weight previously. I find it hard to believe that I was actually jamming something like 100 thou into the lands though. I have a tap to be able to make a spent case for the Hornady COAL tool based on my own brass but I need to order an expander to be able to re-expand the neck. I really want to double check that distance to the lands.
FYI, I previously checked all the pockets with a pocket gauge set and none of them were loose (according to the gauge anyway).
I took a video of my borescope footage in this area, starting from the back of the chamber, to the shoulder, to the neck. There are some pretty rough spots in the neck area and freebore. I believe these are machining marks, but I'm not an expert. Edit: I actually took a video when the barrel was new, those marks in the barrel are machining marks.
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