300 Norma improved fire form process

jenstapio

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Sep 26, 2018
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Nampa Idaho
Hey Roksliders,

Alright I have a 300 Norma improved and run Lapua brass, N570 and 230 Bergers through it. 92.4 grains at around 3096-3100 for final loads and 70 grains N570 with 230s to fire form

I’m curious what other 300 NMI users are doing for their fire form process?

I had one of my pieces of brass show some head separation signs at 4 firings so I started paying closer attention to my brass. I noticed more of my brass showing early signs so I thought maybe I was sizing my shoulders back too much and causing excess pressure. I double checked everything and confirmed I was only sizing back .002 from chamber length. I even started to notice a faint line at the case head/web area after the first fire form through my gun. I have been running 70 grains of N570 with a 230 to fire form it out as my gunsmith who built the gun recommended the lowest powder charge for a standard 300 Norma load to fire form.

I’m stumped as to why I’m getting signs of separation so early? Do I need to go even lower on my powder charge with the 230’s to fireform? How low do you guys go? Or is the Lapua brass just not holding up?

Any input is appreciated!

Thanks

Below is a picture of the brass one fire bottom, two fires in the middle and the top pic is 4 firings.
 

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It's good you're astute and are paying attention to those things. Straighten a paper clip, bend the end at a short sharp 90° angle and drag it along the inside of the case from the bottom up. It'll absolutely tell you the relative degree of separation even if there's no outward sign after fire forming or the first firing.

Obviously any degree of separation and the case is taken out of service. With a belted magnum or any case for that matter, sizing the shoulder back should do nothing for pressure. But since the belt locks the case in, per se, it allows for the forward part of the case to blow forward during forming, each firing then adds a bit to the problem after sizing.

I would seat the bullet up against the lands, that locates the case from the rear and the front while it is expanding to fill the improved chamber.
 

B23

WKR
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Was this a barrel that was brand new or did it start life as a standard 300 Norma and was then reamed to a "improved" version?
 
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Was this a barrel that was brand new or did it start life as a standard 300 Norma and was then reamed to a "improved" version?
Yes, interested as well.

With the 35 Whelen Ackley improved and most other, if not all other improved chambers, the gunsmith sets the barrel back a thread and reams the chamber to the new cartridge . This allowes a slight "crush" fit to the brass when chambering the round. Assures impeccable headspace.
 
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Are you seating the bullet into the lands while fireforming?

Depending on your chamber dimensions you may need to do this to prevent case head seperation.

A quick call to your smith will get you fixed up.
 

Mtnman84

Lil-Rokslider
Joined
Jun 22, 2015
Messages
198
I have worked with many Norma improveds and will be fire forming brass and setting up a few more for friends in the near future. The best process I have found is to remove the extractor from the bolt and run a slight jam on the bullet to have the brass fit firmly against the case head without and pressure from the extractor. I do not bump the shoulder after the initial fireform. I will neck size and make sure they chamber with ease. After the second firing the brass will be fully formed to the chamber and then I will bump the should a thou or two back. With steep shoulder angles you really need to keep the shoulder bump to a minimum. N570 is also really hard on barrels and I would fireform with a cooler burning powder.
 

Mtnman84

Lil-Rokslider
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Jun 22, 2015
Messages
198
The upper node with the 230 Berger is always right around the 92 gr mark. The hybrid and the otm shoot great
 
OP
jenstapio

jenstapio

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Joined
Sep 26, 2018
Messages
54
Location
Nampa Idaho
I have worked with many Norma improveds and will be fire forming brass and setting up a few more for friends in the near future. The best process I have found is to remove the extractor from the bolt and run a slight jam on the bullet to have the brass fit firmly against the case head without and pressure from the extractor. I do not bump the shoulder after the initial fireform. I will neck size and make sure they chamber with ease. After the second firing the brass will be fully formed to the chamber and then I will bump the should a thou or two back. With steep shoulder angles you really need to keep the shoulder bump to a minimum. N570 is also really hard on barrels and I would fireform with a cooler burning powder.
Thanks for the reply this is how is exactly how I have been doing my process. I am going to ensure I have enough bullet jam into the lands. I have been shooting for around .005 of jam but could go more I guess.

Do you have a cooler burning powder you might recommend for fire forming?
 

ducky101

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May 9, 2022
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I have an untested idea that might help address this, in theory.
If your chamber is already set up to be .002-.004 shorter than a standard 300 Norma chamber this would probably not apply.
Anyway, to my idea. Why not add a 1/2 inch O.D, .002 disc shim (with a hole punched out for the firing pin) to the bolt face. This should theoretically give the virgin case roughly .002 of "crush" against the base of the case neck, and keep the case expansion to the shoulder area. And for the 2nd firing, remove the shim and it would already have .002 shoulder bump, then after that 2nd firing it should be perfectly set.
Again totally untested, and might be a terrible idea, but just made sense to me in theory.
 
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I have an untested idea that might help address this, in theory.
If your chamber is already set up to be .002-.004 shorter than a standard 300 Norma chamber this would probably not apply.
Anyway, to my idea. Why not add a 1/2 inch O.D, .002 disc shim (with a hole punched out for the firing pin) to the bolt face. This should theoretically give the virgin case roughly .002 of "crush" against the base of the case neck, and keep the case expansion to the shoulder area. And for the 2nd firing, remove the shim and it would already have .002 shoulder bump, then after that 2nd firing it should be perfectly set.
Again totally untested, and might be a terrible idea, but just made sense to me in theory.
I'm not convinced that this would be effective or practical. However, I am convinced that this is the best 1st post ever in the shooting sub forum here. You get 10 points.
 

Harvey_NW

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Sounds like you may need to set a false shoulder as well.
 

ducky101

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May 9, 2022
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I'm not convinced that this would be effective or practical. However, I am convinced that this is the best 1st post ever in the shooting sub forum here. You get 10 points.
Thanks man, I appreciate it!
Main reason for this idea, is that I am having very similar 1st firing signs as the OP.
First thing I’m going to try is more jam on the bullet and a lighter powder charge.
If that doesn’t change anything, then I’ll most likely give the shim idea a shot.
I have chambered a dummy round with the shim, and it does provide very slight resistance on bolt close.
Original load for reference was lapua brass, 230 Berger, fed215m and 80 grains h1000. Velocity average was 2800.
1st fire form Brass reference as well. The line is very faint but it is there. BB20817B-62EC-450A-9450-D73820D62E63.jpeg
 
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