Into lands or false shoulder to fire form belted brass

[Gwine]

I am getting ready to start load development with some new brass in my 7RM. This will be the first time I have started with new brass in a belted mag.

In order to prevent excess stretch in the new brass I plan on one of the above to hold the base of the cartridge against the bolt face. I have seated the bullet into the lands on some standard cartridges for this purpose before, but am thinking about the shoulder so that I can experiment with seating depths while fire forming.

If you have a preference, can you elaborate.

If the shoulder is the way to go, what is your method. I grasp the idea, but would like to here your practices.

Thanks in advance. I appreciate the knowledge available here.

 

[Dmagna]

Never had any issues will regular loads in my 300 win. You are not really fire forming, in the sense or changing one cartridge brass to another. There isn't a huge amount of issues with the 7 rm that I know of. Should just be able to shoot everything normal.

 

[FURMAN]

I dont understand your question. Just shoot. For the first firing you will headspace off the belt then on subsequent firings you can bump the shoulder to your desired spec. I prefer .002. You will not get "excess" stretch. The brass needs to form to your chamber so you can setup an accurate and repeatable shoulder bump.

 

[bigngreen]

The belt is already doing the job for ya, you won't gain anything from using a method for non belted brass fire forming.

 

[twister]

you have the belt, blast away.

 

[Dean2]

Like all the others have said, belted magnums were actually designed to headspace on the belt. Many people subsequently have them space off the shoulder after the first firing, but realistically one method is no better than the other as long as you aren't over sizing your brass after each firing.

 

[can1010]

first you have to decide if you are going to run the ragged edge and toss the brass in 5 reloads or if your going for a lower node and max brass life.
I have seen belted cases with .012-.017 headspace and for the same reason you would not shoot a non belted case like that I don't fire belted cases like that.
I use a false shoulder but I have the expander mandrels to make it easy to do

 

[Gwine]

Thanks for the replies.

I should have been more clear on my concerns. I do understand the belt will provide for headspace on the first firing. My concern is the ~.013 from case shoulder to chamber shoulder. As I understand it, on the first firing, the entire case (forward of the belt) will push forward to meet the chamber shoulder. Stretching the body closest to the belt.

My thought was to support the case in front of the shoulder so that the growth will happen in the shoulder and not the body.

If I am overthinking this feel free to let me know. I have no desire to add steps if there is not a worthwhile gain. I have been satisfied with 1moa accuracy in my rifles for years, but have stepped up my expectations recently and it has paid off in other rifles.

Thanks again, I do appreciate the replies.

 

[bigedp51]

1. Take a new case that has not been loaded or fired and measure it from the case mouth to the base of the case and write it down.
2. Next take a fired spent primer and start it into the primer pocket with just your fingers.
3. Now chamber the case in your rifle and let the bolt face seat the primer and extract.
4. Now remeasure the case from the base of the primer to the case mouth and write it down.
5. Now subtract the first case measurement from the second measurement. The difference will be your head clearance or the "air space" between the rear of the case and the bolt face. This is the distance the case can stretch to meet the bolt face.

Below using the primer method to measure head clearance or the "air space" between the rear of the case and the bolt face.

Below a British .303 cartridge with excessive head clearance and showing the case stretch.

 

[Gord0]

Load it and shoot. Something I would do though is load and shoot 1 case while only neck sizing until it becomes hard to chamber. Then bump your shoulder back .002". You generally don't get a belted mag fully fire formed in the first couple firings.

 

[Rich Coyle]

Use some.338 Win Mag necked down to what ever headspace you want.

 

[gte901m]

I create a false shoulder on new 7mag brass with a 30cal expander die and a neck sizing die. My rem700 chamber stretches new Win brass shoulders about 20 thousand.

 

[ka30270]

Use some.338 Win Mag necked down to what ever headspace you want.

I guess you would have room for the thicker neck in a factory chamber?

 

[Rich Coyle]

I turn my brass, so I figured he would too.