belted magnum case

alwayswillbe

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Hey guys, I am about to start reloading for the .300 win mag. It is my first time reloading a belted magnum case, is there anything that needs special consideration while doing this? eg slightly different method etc?
 

jrob300

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Re: belted magnum case

Nope. After first firing, headspace off the shoulder like any other cartridge and you're good to go. You may have to FL size to bump the shoulder back enough to chamber or squeeze the body above the belt down enough. If a FL sizer won't do that, you may have to buy a Willis Collet die to squeeze the area above the belt, but I've been shooting WM's for years and still don't own one. I use a Redding body die and have had zero problems.

John
 

jagged77

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Re: belted magnum case

+1 on the Redding body die, I use it in conjunction with a Lee Collet die for the neck on my 300WM and it works out pretty well. I regularly check for thickness above the belt by sacrificing a case now and again plus paperclip method and have yet to see any excessive thinning after 6 firings using this method.
 

MtnCreek

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Re: belted magnum case

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">After first firing, headspace off the shoulder like any other cartridge and you're good to go.</div></div>

+1 The wm's have a lot more play between min spec and actual chamber dimensions compared to other bottleneck cartridges. Sizing to just fit the chamber is more important with this cartridge than most others, IMHO.
 

Kinsman

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Re: belted magnum case

I have been using Lee F/L dies for the 300 WM for years, and have as many as 8 reloads on some Winchester brass, with no problems.
Minimum stretch, very little trimming. Most of my loads are of moderate pressure.
 

Clark

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Re: belted magnum case

The factory chambers are all .220" from the breech face to the end of the belt cut.
The brass is all .215" or less from the case head to the end of the belt.
The should of the brass has an even bigger space to reach the chamber shoulder.

The brass will [on the first firing] be resisting the forward push [of the firing pin] with the belt.

This sounds unsafe to shoot, but the brass will survive the first firing without enough case stretching to cause failure.

Once the case is fire formed to the chamber, on the first reloading, either partial neck size, neck size, or full length size while only setting the shoulder back .001".

The brass will then be resisting the forward push [of the firing pin] with the shoulder.

What not to do:
Adjust the full length sizing die to touch the shell holder, and let the die push back the should as far as it can.
 

MtnCreek

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Re: belted magnum case

Forget the belt; it no longer serves any purpose. You need to size the case to fit your chamber. There's several tools for measuring your fired brass, but you can do w/o, it's just not ideal.

Lightly lube the lower 1/2 of the case body and also lightly lube the inside of the neck. Screw in die till about 1/2" from shellholder. Operate press and look at how far the neck was sized. Continue till the neck is sized all the way to the shoulder (or almost). Give it a try through your rifle to see how it closes; you should feel some slight resistance. You can smoke the shoulder with a cig lighter if needed; that will let you know when the die JUST touches the shoulder. Keep turning in the die (very little at a time) till you get a good feel on the rifle bolt (slight resistance). FYI: If you follow the instructions that come with most FL rifle dies, your brass life will suck down under! Pun intended


Edit: Keep in mind you have an ejector and extractor on that bolt. You'll need to make sure you're not sizing more just because you feel them when closing the bolt. Best advice I think it Just Kiss the shoulder with the die and stop. That should be enough.
 

Boltfluter

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Re: belted magnum case

You can always create a false shoulder for the first firing to maximize case life.
Or seat hard into the lands for the first firing.

Regards, Paul.
 

Clark

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Re: belted magnum case

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: alwayswillbe</div><div class="ubbcode-body">how far should the FL sizing die be away from the shell holder?
the length of the belt?
</div></div>

By having lots of distance between the shell holder and the die, you may be able to partially neck size with the full length die and it still chambers. That is good.
But if the end of neck bumps the end of the chamber from stretch, you must trim.
But if the case shoulder touches the end of the chamber shoulder and makes it hard to re chamber the fired and partially neck sized round, you must bump the shoulder back.
If one screws the die down closer and closer to the shell holder, eventually the sizing process will push the shoulder back .002" in the die and spring back to .001" pushed back when it comes out.

The die thread is 7/8-14. That is a thread pitch of .071"
That is <span style="text-decoration: line-through">25</span> 5 degrees turn per .001" axial.
So if your first piece of brass you are trying to bump gets .003" shorter, you back off on the die adjustment .002" = 10 degrees counter clockwise.


One way to do this is to measure the distance from the shoulder of the fired brass to the case head using a Wilson case gauge and caliper or depth micrometer. Then adjust the die until it changes the measurement on the brass by .001".
 

BK7saum

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Re: belted magnum case

Clark,

I came up with about 5 degrees of die rotation per 0.001" of height change in the die adjustment. If I did my math right...
 

MtnCreek

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Re: belted magnum case

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">You can always create a false shoulder for the first firing to maximize case life.</div></div>

When I read this yesterday, I didn’t really think much about; I’ve always had it in my head the belt was there, so no need to do it. Looking at Clark’s measurements, there’s a least 5tho head clearance when using the belt to set headspace. I don’t know how much life that first firing takes out of the brass, but I may give this a try.

Thanks!
 

Clark

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Re: belted magnum case

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BLK7</div><div class="ubbcode-body">Clark,
I came up with about 5 degrees of die rotation per 0.001" of height change in the die adjustment. If I did my math right... </div></div>
That was way past my bedtime, it did not look right, let me try again.
14 TPI = .071" thread pitch.
360 degrees per turn.
(.071)x 1000 = 71 thousands per thread
360 degrees / 71 thousands per thread = 5.04 degrees rotation / thousandth axial

Uh oh, I will fix my post