28 Nos Flat Primers

MagnumManiac said:

Checked and verified when it was trued. Even if I jam bullets it still does it. Only rifle I've ever seen do it that checked out correctly.
It does it to all primer brands.

Cheers.

Click to expand...

Then the only other thing that I can think of that would do it, other than excessive pressure, is the chamfer around the primer pocket letting the primer flow. I'd compare the chamfer on the Norma against the other brands.
Just curious, have you ever run a pressure trace on that rifle to see where it spikes?

I have a Savage that does the same thing, starting loads to max. Different primers do the same. Haven't tried different brass. Hasn't been a problem, but I'm not typically a "hot rodder" either.

It's not a 28 Nosler known problem.
Is your rifle a custom build?

Hikinghunter said:

Keep in mind that it's flattening primers for all factory ammo (nosler, hornady, Pendleton). So I don't think it's a load issue here. I'm wondering if this is just a thing with 28 nos. But here's a photo some fired handloads anyway.

No noticeable cratering.

Peterson Brass
WLRM primers
175gr Berger Elite Hunters
Retumbo (77.5 to 81 grains, makes no difference in terms of primer flattening).


View attachment 620946

Click to expand...

I don't think it's the 28nosler I have one it dose not do that if it's doing it with factory loads as well as your hand loads you a problem with the rifle ,I hand load for my 28 using n570 in a terminus action I would have it checked out and good luck

I had a similar issue some years back. I never had any bolt swipe but did have the tophat primers. In my case (no pun) It looked as though the radius at the mouth of the primer pocket was excessive or more than normal allowing primers to expand to match the radius. I never had one blow out or any other issue. Have you tried other primers?

I would measure primer pocke depth on new brass, old brass, and if you have a brass that doesn't top hat like that then measure that. It looks like a depth issue to me because of the consistency's. But that's just my thoughts. Let us know if you find the answer.

Hikinghunter said:

Keep in mind that it's flattening primers for all factory ammo (nosler, hornady, Pendleton). So I don't think it's a load issue here. I'm wondering if this is just a thing with 28 nos. But here's a photo some fired handloads anyway.

No noticeable cratering.

Peterson Brass
WLRM primers
175gr Berger Elite Hunters
Retumbo (77.5 to 81 grains, makes no difference in terms of primer flattening).


View attachment 620946

Click to expand...

I'd never want to give bad advice especially when it comes to safety. In this case, I wouldn't sweat it. My 35+ years of loading albeit primarily Weatherby rifles, that looks normal to me even with starting loads. Bolt face and ejector types will always have flatten primers from what I've experienced. Are there any other pressure signs? If I'm out of line at all, I ask any of you with more knowledge to share your thoughts, as I have no ego and only want to give sound advice.

more info- I don't have headspace gauges, but I took a piece of new ADG brass and added tape. With 4thou of tape added there was no resistance to closing the bolt, with 6 thou there was the slightest bit of resistance, with 8 thou you really have to crank it down to close (probably just compressing the tape at that point)

My handloads started with new brass, and after 3x firing my shoulders are about 2though forward (of the shoulder measurement I'm getting from new ADG brass).

My primers are all mixed in a bag now. I'll have to take the rifle to the range and fire some rounds to get primer samples.

I think you are getting a bad measurement over the fired primer. You have to decap the fired rounds before measuring and before sizing to get an accurate measurement. You were previously pushing the shoulder back too much. Back the sizer off about 1/8th of a turn (which is about .008-.009) and start over with good measurements. You already know that you have to increase the length of the shoulder about .004- .006. Don't bump the shoulders at all until they won't go back in the chamber. Then you can get the final correct setting for the die.
For some reason, people seem to be afraid of jamming a bullet in the lands to fireform brass. What happens is, when the firing pin hits the primer, it pushes the brass forward whatever amount the shoulder is undersize. Then it goes BOOM. At that point, the primer backs out from the pressure until it stops at the bolt face, then the case moves back and not only smashes the primer like you see (tophat) but also keeps the brass from fully contacting the bolt face, and then makes the brass stretch at the web instead of blowing the shoulder forward as much, because that is the only way it can move. So, at that point the case really isn't fireformed properly and you still have not filled the chamber. When you jam a bullet in the lands, it helps hold the cartridge against the bolt face and lets the shoulder expand properly.

Ok, so that's a possibility. Still odd that it flattens factory ammo primers.

Hikinghunter said:

Yes, I always de-prime before measuring.

Click to expand...

Then you aren't measuring correctly and your shoulder bump is too much. How are you taking your measurement? With what type of tools? Obviously if you fired the cases 3x and they are still short, you're doing something wrong. Back the sizer off.
Now you have me thinking...how much longer is a fired case compared to a factory unfired case? And then how much longer after you resize? According to your tape measurement, the fired case should be .005 longer before resizing.

Rflshootr said:

Then you aren't measuring correctly and your shoulder bump is too much. How are you taking your measurement? With what type of tools? Obviously if you fired the cases 3x and they are still short, you're doing something wrong. Back the sizer off.
Now you have me thinking...how much longer is a fired case compared to a factory unfired case? And then how much longer after you resize? According to your tape measurement, the fired case should be .005 longer before resizing.

Click to expand...

Hornady OAL guage with the anvil base on a Mitutoyu caliper. De-prime, put it in the guage, wiggle/twist until the numbers settle down.

The brass isn't fire forming 5 thou. The shoulders might move forward 1-2thou after firing. So it would take several rounds of neck sizing only to fire-form. Will definitely admit that I had a bit of learning curve starting out, but the last time I loaded the brass started at 2.235 and fire-formed to 2.236 (virgin brass is 2.234, and if it fire-formed to fill the chamber it should be close to 2.240)

And why is it flattening factory ammo primers?

Another dumb question. What action, custom or stock?

I'll cut to the chase and then provide my support. Nothing is "wrong". You and the factory are doing things "by the book". The end

but there is always "more".

I have 4 Nosler variants from 2014 on. They are "My version" because I didn't have to conform to "Factory rules" when specifying my reamers. 277/26-Nosler, 28 Nosler, 308/26-Nolser and 338/26-Nosler. I just recovered my original designs from the computer I was using back in 2014 when I did them. I did "paper" experiments from .243 to .375 but only built the 4 so far.

I provided that because I have probably a thousand or so rounds down range and 2 elk with them. Add to that the bench rest 300 RUM and ELR games 338/300 RUM and I am familiar with the behaviors of these types magnums. BTW: It would be more rounds down range but I am just returning to shooting after being away from it for 6 years track riding motorcycles.

back to the problem at had...

I remember seeing this before, mostly in these "Ultra Magnum" type setups. It's not a "problem" per say, it is an indicator of factory "error on the safe side", meaning. it's not really and error or problem at all. Your handloads on new brass duplicating the behavior falls in the same category.

Those that suggest "measure your chamber". There is some validity to that but it will not indicate any "problem", don't worry about that. If there were a real problem there it would show as something else.

Looking at your unfired, is it factory? and fired.

My belief based on pictures, description and information provided agrees with @Rflshootr.

The primer pocket has a nice champher to it. Based on the pictures of the primers, it is what I expected.
There are no excessive pressure indicators in the pictures. Pictures can be deceiving but I don't think this is the case.

There is high speed videos of what is going on so @Rflshootr is not conjecturing on the process. During the firing process, the ejector is holding the brass away from the bolt face, the pin strikes the primer and the ignition process begins. The primer backs out a few thousandths, then the brass expands to fill the chamber pushing the cartridge head back against the bolt face. The primer is "under pressure" so does no go back into the pocket and instead "mushrooms" a little. No problem.
If it were me, and it was back when...

Measure fired brass after punching the primer with just a decapper. As described by @Rflshootr, this will indicate that you probably want to "bump shoulder" less.

Make up a couple rounds with this now slightly longer case and see if the behavior goes away.