300 Norma Mag - Overpressure Signs Due to New Norma Brass???

[mtwalsh367]

I was breaking in a new 300 NM and noted over pressure signs with the brass, even with light loads - 83 grains Retumbo with 230 Bergers @ 2850. I checked all my tolerances i.e. neck clearance of .003, headspace of .0015, etc. I was flattening primers and was getting some gas past the primers even at 83 g and was worse at 84 and 85 grains. I was using new brass and noted that the primers seated very very hard so I resized the primer pockets on some of the new brass and this helped a little with the hard seating but was still getting over-pressure signs with the brass. So I took my now once fired brass and full resized it, including primer pockets and reloaded 25 rounds varying from 83 to 85 grains once again. To my surprise the over-pressure signs magically disappeared. Primers were not at all flat and no signs of gas getting past primers on all 25 rounds. I'm using Fed 215 primers.

I have never experienced anything like this before. I am using Norma brass, purchased about 6 months ago. I'm concluding there is something wrong with the primer pockets on my brass or the brass hardness is somehow out of whack. I've heard the 300 NM is hard on brass but seems odd to have a problem with new brass. I'll work up 25 more rounds with the reworked brass to confirm the overpressure signs are gone. Maybe I'm drawing a wrong conclusion and there is something else that is factoring in?

Any thoughts???

 

[EXSOCAL]

This is interesting to me... I seem to be having the exact opposite problem and have pressure signs, sticky bolt lift and stuck cases with my 1x Norma brass and nearly the same load - 83.8 gr Retumbo and a 230 Berger...

I gave up on the Norma brass because it seemed like the necks were too thick. Are you expanding and re sizing the new Norma brass or just loading as is? It could be that you have too much neck tension that’s giving a spike in pressure...

On a side note, I switched to Hornady brass and have had much better luck. I’m on my 4th loading of a batch of cases and primer pockets are still nice and tight.

 

[linedrive301ft]

Possibly a difference in internal H2O capacity. Older brass may have more.

 

[mtwalsh367]

I did not work the new brass other than to resize the primer pockets on 25 rounds and no resizing primer pockets on 25 rounds but that did not cause any difference in my problematic pressure results. The bullets seated very easily and consistently in the new brass. So far it seems that the 83.8 Retumbo is my best load, although 85.5 is looking like a potential. So I was out today with another group of 25 of my once fired brass. Based on not having pressure signs last time out with once fired brass going up to 84.4 grains I went ahead and tested up through 86 grains which was right at 2990fps. As I saw Friday there were no pressure signs either with bolt lift or flattened primers or any leaking gas past primers. So I'm cleaning my brass right now and will see if the third loading goes well. Hopefully my primers are still snug and I continue to not have pressure signs. I have 200 pieces of the Norma so after that hopefully either the Lapua is out or I'll give Hornady a try. Since I purchased my Norma brass at 2 different times (100 pieces each) maybe I'll have better luck with the second batch of 100.

Is your 83.8 load still seeing pressure signs with the Hornady brass or was that just the Norma brass?

 

[mtwalsh367]

I think on the next batch of new brass I will resize the necks before firing. Maybe it was a neck tension issue even though the bullets seated pretty easily.

 

[bjay]

I think you're below minimum load.. something isn't right

 

[EXSOCAL]

My 83.8 gr Retumbo load is holding solid in the Hornady brass. I made it to 85.8 grains before I ran into heavy bolt lift and flat primers. My 83.8 grain load nets me 2960 from a 28” bartlein with the 230’s seated 40 Off, which puts em right where they need to be at the neck / shoulder junction.

For some reason the load data out there never came close to what I experienced first hand. I run into pressure and have much higher velocities than what they list... For comparison, factory 230 grain ammo by ABM runs about 2940 through my gun.

I have around 500 rounds through my Norma and I’m honestly not completely sold on it yet. My rock solid 300 win mag load of 73.8 gr H1000 and a 215 Berger at 2850 is pretty tough to beat, especially when you consider the Winchester win mag brass is cheap compared to any of the Norma brass. I was hoping for a bit more out of the velocity and case life. Accuracy is good but nothing I can’t get my win mag to do. I’m still optimistic and trying to get it dialed in. Hopefully you have good luck with yours. Lots of people out there like the cartridge.

 

[mtwalsh367]

I've seen this Berger load chart before being circulated online and its not in my latest Berger manual. I also have seen various comments that say its way off and dangerously high. Maybe its just the Retumbo numbers that are high, I don't know. At 86 grains of retumbo I'm experiencing 3000 fps with a 25.5 inch barrel which is 125 fps over what this chart says I should be at 89.1 grains retumbo. I don't see too many people talking about going above 3000 fps so I'm not going to push above that without other solid sources of load data.

I did measure my new unfired brass neck OD and its .002 smaller than my bushing die size so I think maybe I should have ran an expander through the necks before firing the first time. I'll do this on my next batch.

 

[SPAK]

What’s your headspace like on new brass? Measure new brass vs 1x fired... sometimes excessive headspace can mimick overpressure.

 

[Jack_Australia]

@mtwalsh367 Did you come up with a reason for the pressure signs? Under minimum load? I've just had the same issue with 83 gr Retumbo, Federal 215 primers, 230gr Berger VLD .020" off the lands. I used Peterson brass. Fired one shot at 2808fps and have clearly visible marks from both the ejector and extractor. I'm hesitant to continue with my load development at this point..

 

[918v]

If the bullets seated easily into the unfired necks then neck tension is not the cause of the blown primers. My thinking is you’re too close to the lands.

 

[Jack_Australia]

I'd have thought. 020" would be an adequate amount of jump. The bullets seemed to feel the same as other cartridges I've loaded for, perhaps a little tighter, ill do some mesuring... The primer remained intact, just a little flat.

I'd have expected to get a much higher velocity seeing as the pressures are high enough to leave an imprint of the bolt face. Could I possibly be on the edge of a secondary explosion effect?

 

[918v]

No.

What’s the headspace new vs fired?

 

[Jack_Australia]

I'll get back to you with that information in the next few days as I'm not near the rifle at the moment. I'm hoping there is no massive difference! Rifle has only just been assembled. I'm not sure if it is related, but subsequent chambered rounds have rub marks on the bearing surface on the ejection port side only. I chambered a round with finger pressure and then closed the bolt on it to eliminate pressure exerted by the ejector pin and extractor claw as potential causes on chambering. It still occurred. This didn't happen on any of the dummy rounds that I made up while finding the lands. Not sure if something may have caused it when I fired the overpressure shot. Any ideas? It may not even be related? Can post a pic if needed.

 

[Milo 2.5]

I've seen this Berger load chart before being circulated online and its not in my latest Berger manual. I also have seen various comments that say its way off and dangerously high. Maybe its just the Retumbo numbers that are high, I don't know. At 86 grains of retumbo I'm experiencing 3000 fps with a 25.5 inch barrel which is 125 fps over what this chart says I should be at 89.1 grains retumbo. I don't see too many people talking about going above 3000 fps so I'm not going to push above that without other solid sources of load data.

I did measure my new unfired brass neck OD and its .002 smaller than my bushing die size so I think maybe I should have ran an expander through the necks before firing the first time. I'll do this on my next batch.

Not sure if I can find it, but Berger has came out and said this data is not right, too hot. I browsed their website and cannot find a revised version. A call or email to them may yield some better info. I do know going off Quickload for 300 Norma can get you in a bind quickly too.

 

[Jack_Australia]

No.

What’s the headspace new vs fired?

It's a head space issue. Fired case is 0.020" longer at the shoulder. Looks like the shoulder angle has sharpened too!

 

[Bradu]

It's a head space issue. Fired case is 0.020" longer at the shoulder. Looks like the shoulder angle has sharpened too!

Do you have an improved chamber? That's what it sounds like if the shoulder angle is changing. Post pics of a fired round next to an unfixed piece of brass.

 

[Jack_Australia]

Note the ejector post mark on 'Magnum' and extractor recess mark over 'Peterson'.

 

[SPAK]

If it truly is .020” of headspace that will give you your excessive pressure signs and ejector wipes. Or the brass is out of spec....

If you want to be sure find someone with headspace gauges if your Smith is not local.

I’ve had this exact issue with a particular rifle that had a jacked up chamber. Headspace was .020” too long.

Personally, I’d have the chamber fixed by the smith who did the work..... if you trust them to fix it

 

[Jack_Australia]

If it truly is .020” of headspace that will give you your excessive pressure signs and ejector wipes. Or the brass is out of spec....

If you want to be sure find someone with headspace gauges if your Smith is not local.

I’ve had this exact issue with a particular rifle that had a jacked up chamber. Headspace was .020” too long.

Personally, I’d have the chamber fixed by the smith who did the work..... if you trust them to fix it

I contacted the smith and told them about the issue. I've sent the fired case to them as they are not local for their inspection.

 

[Jack_Australia]

Gunsmith got back to me. Peterson brass is .016 short and has the incorrect shoulder angle. Now I need to find a load for some cheep pills to fireform my brass. Any suggestions?

 

[Milo 2.5]

Gunsmith got back to me. Peterson brass is .016 short and has the incorrect shoulder angle. Now I need to find a load for some cheep pills to fireform my brass. Any suggestions?

Gunsmith got back to me. Peterson brass is .016 short and has the incorrect shoulder angle. Now I need to find a load for some cheep pills to fireform my brass. Any suggestions?

Glad you got it nailed down, easy fix.