Belted Magnum Headspacing

[bronco9588]

Hi all,

I have a 300 win mag. I purchased some go and no go gauges from PTG and some cheap PPU ammunition for break in. This is more of a gunsmithing question but has relevance to reloading. I did a comparison of the 3 head-spaces of the brass, the go, and the no go gauge. Notably, Head space for the belted magnum is from the bolt face to the bore end side of the belt. It is not the shoulder for belted magnums. This is somewhat a new concept for me as I have just gotten familiar reloading the 308 Winchester which is based off of the shoulder. Anyways, went to do a visual inspection of their belt heights. For comparison with the eye, I took computer printer paper and shimmed the brass to the go gauge and the go gauge to the no go gauge and checked their level.

Interestingly, I have a hard time telling the difference between the head space gauges. By the test, the difference is 1 slice of paper. Now the prvi brass took three slices to get to the go gauge and therefore 4 to get to the no go gauge.

1) Is it typical to have really similar set of gauges yet somewhat far off brass? I mean if min and max is within a sheet of paper and the brass is 3-4 papers off, wouldn't that be somewhat harmful to the boltface/ overwork the base of the brass? Is is possible that the brass or the gauges are out of spec?

2) Since the rifle is a bolt action, and the head space is not based off of the shoulder, I think that fire-forming/ just neck dieing the brass will allow me to have a custom fitting shoulder to the chamber. Theoretically less cold working the brass for longer life, and potentially more accuracy. Moreover, redundancy with "headspace" as the belt and the neck would keep the brass from moving around. Is that typical of belted magnums or do people still like to full length die them?

 

[bigwheeler]

Re: Belted Magnum Headspacing

Belted brass only headspaces off the belt when new. After it fire forms it should space off the shoulder like any other brass.

 

[Fuzzball]

Re: Belted Magnum Headspacing

Ditto. We are reloaders, not gunsmiths or manufactors. We adjust our dies so all bottle neck cases "headspace" at the shoulder.

 

[jwoolf]

Re: Belted Magnum Headspacing

You ALWAYS want to headspace off the shoulder... especially with a 300wm. If the shoulder has to go too far to get to the end of the chamber, you're stretching the case severely at the case head... this is also very hard to resize with a belted magnum. It usually doesn't resize enough in the belt area and ends up bulging after a few firings. Novice reloaders can get case heads split and that is NO FUN. You want to be pretty careful with belted magnum brass and treat it as well as you can and don't over work it if at all possible.

A 300wm can space off the belt, I suppose if there is too much bulge at the belt.

I make sure that never happens by using a belted magnum collet resizing die to resize the belt area to make sure this never happens. If you're getting a signifigant bulge at the case head, you may end up bumping the shoulder way too much to get the headspacing incorrect just to "unbulge" the case head.

By collet sizing the case head back down, I bump the shoulder .002 and, I get GREAT case life out of my brass that way. It's an extra step but, it's worth it in my opinion. To do this you take a fired round that has been fired in your rifle... measure the headspace of the brass, then FL resize it ( only bump the shoulder .002 back), then put it in a collet resize die and fix the belted area. You'll find that you get a nice chamber fit with virtually no play but, the round will chamber with no effort.

This is the collet die I'm talking about: http://www.larrywillis.com/

He's got a headspace gauge there too but, there are others that will also allow you to do this but, I wouldn't advise a "go no go" gauge... they don't give you exact measurments and, a "go no go" gauge" isn't your rifle's chamber size.

 

[bronco9588]

Re: Belted Magnum Headspacing

I guess the question remains, is the ppu ammunition going to hurt the rifle on the first firing? Yea, the brass will get a lot of expansion and cold working. Maybe with good annealing, this should not be a problem? With just neck sizing thereafter?

 

[former naval person]

Re: Belted Magnum Headspacing

No, the question doesn't remain as such. On the first firing the ammo will STRETCH to fit the chamber. That won't hurt the rifle. The stretch is about 3/8" above the base. The reason that happens is that the case, upon firing expands to fit the forward part of the chamber. The base is driven backwards to stop on the face of the bolt.
The expansion issue is determined by the diameter of the chamber v/s the unfired diameter of the brass. You NEVER anneal brass down that far...so annealing will not help. Neck sizing will help extend brass life, but at some point you will have to full length size. At that point, only bump the shoulder back .002" or so.

 

[Fuzzball]

Re: Belted Magnum Headspacing

"I guess the question remains, is the ppu ammunition going to hurt the rifle on the first firing?"

I guess we have two options with new cases; fire them...or not; I've always fired mine!

 

[bronco9588]

Re: Belted Magnum Headspacing

I see your point, but what is the point of measuring the head-space based off the belt (that is slightly a rhetoric question)? Furthermore, for a head space based off a shoulder, I thought that there were go and no go gauges (and field gauges) for a reason. To prevent case head separation and to protect the shooter? In a round about way, why do we even care?

 

[Fuzzball]

Re: Belted Magnum Headspacing

<span style="font-style: italic">"I thought that there were go and no go gauges (and field gauges) for a reason. To prevent case head separation and to protect the shooter?"</span>

Those gages you have certainly have valid uses for manufactors and gunsmiths cutting/checking chambers; they must know if the chamber is reamed within safe standards and if the locking mechanism has worn too excessively for safe use with standard ammo. But checking the headspace is rarely a problem with a modern rifle. We reloaders can - and should - size our fired cases to match what our chambers ARE, not what some chamber gage says they 'should be'. IF we do that correctly the actual headspace is virtually irrelivant because the ammo fits as it should no matter what the headspace is.


<span style="font-style: italic">"In a round about way, why do we even care?"</span>

So far as actual chamber headspace goes (and if the locking system is okay) we don't, or at least very rarely is that a valid problem. Most of us have come to use the simple case 'headspace' gages such as the Hornady or Sinclair that work on a precision dial caliper so we can match the fired shoulder location to the resized location and that's all we need to do.

 

[FLIGHT762]

Re: Belted Magnum Headspacing

The point of head spacing off of the belt originally was with the 300 H & H magnum and the 375 H & H belted magnums, since there was no shoulder to head space off of. Most all of the subsequent cartridges based off of the belted cases do have a shoulder to head space off of. The belt is not needed. It was marketing hype many years ago to have "Magnum" cartridges with a belt. There were a few belt less magnums in Europe and a few in the US, but they never gained popularity here.

It wasn't until a few years ago that belt less magnums were marketed here in the U. S. and have gained popularity.

What you need to do is to get a cartridge head space measuring tool such as the Hornady, Sinclair, Innovative Technologies etc. that measure the stretching of your brass NOT head space gauges (they are used to determine too much or too little head space in your rifle's chamber and that the chamber is within SAAMI specifications).

When you fire your new ammunition, you take the fired cases and measure the length/ expansion of the shoulder datum line on your fired cartridges. You then resize your cases to only bump the shoulder back about .001"-.002".
If you don't measure this, you can bump the shoulder back too much, causing short case life / case head separations.

You need to find someone in your area that can mentor you and get you going on the right track. There's lots of information on the internet on how to properly set your dies to F/L size and bump the shoulder back minimally. As another poster noted, you can neck only size a few times, but after 4 or so firings, you need to F/L size or risk getting a loaded cartridge stuck in your chamber.

I once had a .338 Winchester Magnum that I hand loaded for when i was new to reloading. I would get about 3 firings before getting case head separations. I didn't have any tools at the time to determine how much i was bumping the shoulders back. I was likely bumping them back way too much and caused over stretching of the brass, which caused my separations.

 

[bronco9588]

Re: Belted Magnum Headspacing

I really think I need to get a headspace tool... for the time being, I plan on getting a nice set of redding neck dies and getting about two additional shots before a splurge on the higher end reloading equipment. I think it will also serve as a good way to pool up some brass before dropping some money on an annealer and full length die and headspace tool.

I would love to find a mentor. I have been pretty much self taught on the subject and do A LOT of reading. I have done 308 Winchester and 40 s&w because I had those guns to test with. I have used a caliber specific case length gauge to set my shoulders, and I think I would take calipers in the gauge to measure expansion, but it has been a while.

As far a belted cartridges go, I feel like there are some specific tricks to the cartridge that I am not really familiar with.

 

[Clark]

Re: Belted Magnum Headspacing

There are some belted magnums the have the same SAAMI spec:
.220 - .008" for cartridge
.220 + .007" for chamber
6.5mm RemMag
7mm RemMag
8mmRemMag
264 WinMag
300 H&H Mag
300 WinMag
338 WinMag
350 RemMag
375 H&H Mag
458 WinMag

When I measure the brass, it is typically between 0.210" and 0.215".

So when I headspace a belted magnum rifle, I headspace it at 0.215"

My factory guns are more than .220".

link to Bart Bobbitt post on belted magnums

Bart Bobbitt:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Both military and civilian top marksmen tried full-length sizing fired
cases such that they would headspace on the belt, but accuracy wasn't
as good. They tried neck only sizing; same results, often worse. Yes,
I know the long range benchresters liked to neck size their cases, but
they also got groups ranging from 4 or 5 inches up to over 12 inches
evidenced by their 3- to 5-group aggregates (averages). The problem
was the fired cases had an extra step in front of the belt. When the
firing pin drove the case forward to stop with its belt against the
chamber headspacing step and burning powder expands the case, the case
shoulder gets pushed forward against the chamber shoulder. Then the
case head gets pushed back against the bolt face taking the belt with
it and the case body immediately in front of the belt expands against
the chamber wall.</div></div>

 

[jwoolf]

Re: Belted Magnum Headspacing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bronco9588</div><div class="ubbcode-body">I really think I need to get a headspace tool... for the time being, I plan on getting a nice set of redding neck dies and getting about two additional shots before a splurge on the higher end reloading equipment. I think it will also serve as a good way to pool up some brass before dropping some money on an annealer and full length die and headspace tool.

I would love to find a mentor. I have been pretty much self taught on the subject and do A LOT of reading. I have done 308 Winchester and 40 s&w because I had those guns to test with. I have used a caliber specific case length gauge to set my shoulders, and I think I would take calipers in the gauge to measure expansion, but it has been a while.

As far a belted cartridges go, I feel like there are some specific tricks to the cartridge that I am not really familiar with. </div></div>

With the 300wm, annealing becomes pretty important... I anneal after 2 firings, I bump the case head every firing and, I FL resize every time and bump only .002 from the reference of a fired case in my rifle. By not bumping the case head with the special collet die, you have to be pretty careful because that bulge in the back of the case gets to the point that you may separate a case head simply because you're not resizing that part of the case. ( I've never done that, however )

With a magnum case, you want to anneal for two reasons, your ammo is much more accurate when you anneal properly ( and get consistant case sealing in the chamber and consistant bullet release )and, you won't split the necks on the cases. By only bumping .002, you keep from overworking your brass and, by collet resizing the case head, you keep the brass from forming a ring around the inside of the case where is a weak point in the brass that may separate at some point in the future. ( some guys here use a paper clip and stick it inside of a case that's been fired several times and use the paper clip to see if they're forming a crease at the inside of the case around the belt area... if you find a crease, you throw the case away immediately )

I only anneal my 308win about every 5 firings but, I anneal my 300wm every second firing. Reloading accurate ammo is a labor of love for the guys that want to shoot accurately.

You really have to become OCD with your methods with reloading. It's all about consistancy. All of this we're talking about here are tried and true methodology.

Can you load ammo that will go bang and shoot ok without doing all of this and using a simple go/nogo gauge? Sure you can and, if you don't want to shoot your cases more than about 4 times, that's fine. If you want to shoot them more than that, you're going to have to anneal. You can, with the right dies not have to do the case heads and, I know several guys that don't do that part. I think redding dies ( which I also use ) may be able to get the .002 bump on the shoulder without HAVING to collet size the case head ) I just choose to do this part also. It gives me another piece of mind knowing that my brass is 100% consistant and I will never separate a case head.

I hate prepping brass the first time because, I turn the necks and work the primer pockets etc. etc. etc. and, most of that you only have to do one time.... I get 15+ loadings from my brass by being careful with it. Not to mention that I load VERY accurate ammo this way.

PS: it won't cost you a fortune to anneal brass... you can simply use an electric drill and the appropriate long socket and a 15.00 propane torch from wallyworld. Here's a good article on annealing: http://www.6mmbr.com/annealing.html

 

[mdmp5]

Re: Belted Magnum Headspacing

Ok, listen. Yes, new 300wm brass headspaces off the belt alone, with a lot of swimming room in front of the shoulder. After the case is fireformed, it is true that the shoulder blows out to the dimensions of the chamber. But if a 300wm case was headspacing solely off the shoulder, then the bolt would not close. That means that the belt would not be making contact with the outside rim of the chamber, and there wouldn't be enough headspace. So in reality, the most you are doing is splitting the responsibility of headspacing between the belt and the shoulder; they are both making some contact.

 

[jwoolf]

Re: Belted Magnum Headspacing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: palmik</div><div class="ubbcode-body">Ok, listen. Yes, new 300wm brass headspaces off the belt alone, with a lot of swimming room in front of the shoulder. After the case is fireformed, it is true that the shoulder blows out to the dimensions of the chamber. But if a 300wm case was headspacing solely off the shoulder, then the bolt would not close. That means that the belt would not be making contact with the outside rim of the chamber, and there wouldn't be enough headspace. So in reality, the most you are doing is splitting the responsibility of headspacing between the belt and the shoulder; they are both making some contact. </div></div>

Yep. That's kind of my point. It's possible to really screw up if you're just screwing down the reiszing die till you get a case to fit in your rifle.... you could bump back the shoulder .020 and have no idea that's what you've done because you just ended up sizing the belt area till the case fit in the rifle again.

That's why I resize the head area AND only bump .002.

I do know guys here successfully only bumping the shoulder .002 that get their bolts to close pretty well, however. I'm sure not all die sets will allow this, however....AND, you're still going to have a bulge in the case head that will form a ring at the inside of the case where the die stops resizing.

I've learned most of my life from the school of hard knocks and, I've finally come to the conclusion that with all stuff that matters a lot to you... invest in the right tools to do the job properly. By a Chinese scope and, you get poor results... by cheap ... well anything and, get cheap results.

Read, read, read, listen and learn and buy the right stuff the first time and learn from the 500yrs of experience that rifles and accuracy has evolved into... there are so many on this site with knowledge that are more that willing to share.

Hell, I went to Camp Perry 8yrs as a Jr. Shooter sponsored ( National Jr. Team...made the president's 100 in 1984 High Power National Match course )..... I'm new by many folks' standards here.

 

[Clark]

Re: Belted Magnum Headspacing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: palmik</div><div class="ubbcode-body">Ok, listen... But if a 300wm case was headspacing solely off the shoulder, then the bolt would not close. That means that the belt would not be making contact with the outside rim of the chamber, and there wouldn't be enough headspace. So in reality, the most you are doing is splitting the responsibility of headspacing between the belt and the shoulder; they are both making some contact. </div></div>

I do not follow.

In my factory guns the new brass is way more than .005" from touching the shoulder and more than .005" from touching the belt.

The firing pin pushes the new brass more than .005" forward until the belt touches the chamber, the shoulder does not touch, the cartridge stops moving forward, the case fills out and grips the walls, and the case stretches and slips back to touch the bolt face.

Now if the shoulder is pushed back .001" with a FL die, the the firing pin only has to push the case .001" to touch the shoulder, but more than .004" to touch the belt, so it does not touch the belt.

So with factory chambers and new brass, the case belt touches the chamber on the first firing, and the shoulder touches the chamber on subsequent firings, if resizing is done with due diligence. All bets are off if you are they type to bump the shell holder with the die.

If there is sharing, it is not concurrent, but sequential on different firings.

.220 - .008" for cartridge belt
.220 + .007" for chamber belt clearance
---------------------
Belt specified to have between .000" and .015" clearance

2.2700 - .0070" for cartridge shoulder clearance
2.2791 + .0100" for chamber shoulder clearance
---------------------
Shoulder specified to have between .0091" and .0261" clearance

What does it all mean?
The belt has big clearance.
The shoulder has bigger clearance.
The firing pin pushes the belt against the chamber.
The case fires.
The case shoulder expands.
Then the shoulder has no clearance.
But the belt still has big clearance.
Next time the firing pin pushes, the shoulder touches, but the belt does not.

 

[bronco9588]

Re: Belted Magnum Headspacing

Is it desirable for the case to float around in the action? This allows for all but the most precise ammunition to be cycled? My question is why does the should need to get pushed back .001"? Does the brass float forward and then back, or stretch back? My apologies if these questions sound trivial? I have always imagined the brass not moving in the action. I feel there is a paradigm shift in the making...

 

[jwoolf]

Re: Belted Magnum Headspacing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bronco9588</div><div class="ubbcode-body">Is it desirable for the case to float around in the action? This allows for all but the most precise ammunition to be cycled? My question is why does the should need to get pushed back .001"? Does the brass float forward and then back, or stretch back? My apologies if these questions sound trivial? I have always imagined the brass not moving in the action. I feel there is a paradigm shift in the making... </div></div>

Even imprecise brass can be fired and be ok.

The point of this thread to me is to show that you can't do that over and over to brass and expect it to do what it did on it's first firing. The first time it's fired, it's set to a spec that will go bang in anyone's rifle safely. If you're reloading for YOUR rifle, you NEED to learn how to treat your brass and only bump .002. This will assure better accuracy and better case life and you won't over-work your brass.

Many don't do the case head stuff I've talked about here. I do. You choose if you think that is important to you BUT, I do advise you to get a good measuring tool and know what you're bumping your shoulder to. If you find that after bumping the shoulder only .002 and you have trouble closing the bolt then you have a case head issue.

Brass gets work hardend.. the more you work brass the harder it gets. You anneal and, unlike steel and some other metals, if you heat brass to the right temp, you soften it some. The qualities of brass make it unique to most other metals and that is why it has been picked to be rifle brass.... when you heat it it softens. Heat it the right amount around the neck area and you renew it.

Brass moves in the action... the idea is to have it move least possible. So, you're only talking about .002 of an inch.... that a very small movement.

With a belted case, basically only have to worry about the shoulder AND you have to worry about case head stuff... If you choose NOT to worry about the case head then you need to watch for the crease that gets in the belt area inside the case and check with a paper clip or some other thing that will help you see this issue... regardless, with a magnum, I'd suggest learning how to anneal.

If you're willing to throw your brass away after 4 reloadings then, forget this whole thread and just load them... If you're trying to get the ultimate ammo. then listen... learn how to turn case necks, anneal, debur flash holes, learn how to clean primer pockets and, learn how to get consistant neck tension... etc. etc. etc.

On a good day at 1000yds, I can hit as many 4" clay pigeons as I miss but, you HAVE to not skip steps in your process to even get close to this kind of accuracy and you have to have a rifle capable of it also.

I don't know what kind of rifle you're shooting etc... if it's a hunting rifle and not a custom job then, it may not make sense for you to go to all this trouble.... if that is the case, buy your brass and reload it 4 times and throw it away.

Remember your audience.... we're the guys that do know how this whole thing works and, you're asking a question in this arena. We're giving you the answers... it may seem like a lot of trouble but, that's becuase it is... it's a big pain in the ass but, it's required to make ammunition that is accurate enough for a head shot at 1000yds... or farther.

 

[bronco9588]

Re: Belted Magnum Headspacing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jwoolf</div><div class="ubbcode-body">
With a belted case, basically only have to worry about the shoulder AND you have to worry about case head stuff... If you choose NOT to worry about the case head then you need to watch for the crease that gets in the belt area inside the case and check with a paper clip or some other thing that will help you see this issue... regardless, with a magnum, I'd suggest learning how to anneal. </div></div>

Is there such thing as a body belt separation? The cases thin out right above the belt?

 

[jwoolf]

Re: Belted Magnum Headspacing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bronco9588</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jwoolf</div><div class="ubbcode-body">
With a belted case, basically only have to worry about the shoulder AND you have to worry about case head stuff... If you choose NOT to worry about the case head then you need to watch for the crease that gets in the belt area inside the case and check with a paper clip or some other thing that will help you see this issue... regardless, with a magnum, I'd suggest learning how to anneal. </div></div>

Is there such thing as a body belt separation? The cases thin out right above the belt? </div></div>

The cases get a crease where the die stops resizing the case. The case keeps growing but, the die doesn't resize that part and, at the point where the die stops, there becomes a crease.... when this becomes prounounced, you should throw the case away.

 

[bigwheeler]

Re: Belted Magnum Headspacing

The line where the die stops has nothing to do with where the case head separates
from over stretching. They separate where the webbing thins down to the case
wall thickness. That is the line you will feel inside with a bent wire tip. You can see
it from the outside a firing or two before it comes apart.

 

[jwoolf]

Re: Belted Magnum Headspacing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bigwheeler</div><div class="ubbcode-body"> The line where the die stops has nothing to do with where the case head separates
from over stretching. They separate where the webbing thins down to the case
wall thickness. That is the line you will feel inside with a bent wire tip. You can see
it from the outside a firing or two before it comes apart. </div></div>

I'll take your word for that, Sir. If it is the same place or not, it really makes no difference.. it's ABOUT the same place... if it comes apart right at the top of the belt or where the die stops, it's still a case head explosion. LOL But, I do take your word on that one. I do size the case heads on my ammo to, hopefully, keep my from having this issue.

I've been lucky and never had one do that to me... yet.

I've felt the ridge that happens in the case and thrown them away, however but, I didn't look exactly where that was happening...

Honestly, since I've been resizing the case heads, I haven't had to replace any brass in a long while.

I've been getting so many reloadings out of my brass that isn't reloaded too hot that I wear out the primer pockets befoue I have other issues.

 

[Clark]

Re: Belted Magnum Headspacing

1) Got split necks?
The reamer and/or dies must have been built to SAAMI specs.
What are the options to avoid split necks?
a) custom small neck reamer and dies that make .001" of neck tension
b) anneal necks
c) buy new brass

2) Got case head separation in a belted mag?
The rifle must have been headspaced with SAAMI specs.
What are the options to avoid head separation?
a) Headspace rifle to fit brass available
b) Push the shoulder back .001" when resizing
c) buy new brass

Did I miss anything?

 

[mdmp5]

Re: Belted Magnum Headspacing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Clark</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: palmik</div><div class="ubbcode-body">Ok, listen... But if a 300wm case was headspacing solely off the shoulder, then the bolt would not close. That means that the belt would not be making contact with the outside rim of the chamber, and there wouldn't be enough headspace. So in reality, the most you are doing is splitting the responsibility of headspacing between the belt and the shoulder; they are both making some contact. </div></div>

I do not follow.

In my factory guns the new brass is way more than .005" from touching the shoulder and more than .005" from touching the belt.

</div></div>

If the brand new brass is not headspacing off the belt, then what is it headspacing off?

 

[Clark]

Re: Belted Magnum Headspacing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: palmik</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Clark</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: palmik</div><div class="ubbcode-body">Ok, listen... But if a 300wm case was headspacing solely off the shoulder, then the bolt would not close. That means that the belt would not be making contact with the outside rim of the chamber, and there wouldn't be enough headspace. So in reality, the most you are doing is splitting the responsibility of headspacing between the belt and the shoulder; they are both making some contact. </div></div>

I do not follow.

In my factory guns the new brass is way more than .005" from touching the shoulder and more than .005" from touching the belt.

</div></div>

If the brand new brass is not headspacing off the belt, then what is it headspacing off? </div></div>

Who says new brass is not headspacing off the belt?

 

[bignada]

Re: Belted Magnum Headspacing

I've owned two magnum ctg RCBS Precision Mics. The 7mm rem mag was shorter than the .300win mag but both shared the same thimble top piece for checking headspace.

The Precision Mic is not as precise as the Wilson Case Gauge. The P-Mic is threaded and marked like a micrometer to show an OAL measure. Measure your virgin brass, and then measure your fired brass. I have seen a helluva lot of brass growth on that first shooting. The growth is the case stretching to fill your magnum chamber...

I've seen unfired, virgin brass measure as much as .015 below the -0- base index mark, and when fired it grows .02"... Maybe don't seem like much but, WOW!

Only magnum of any kind I continue to shoot is the .338/300win. I improve standard .338win chamber with the reamer and use a virgin case as my go gauge. The case then headspaces on the shoulder and does not grow when fired.

If you can't use a magnum reamer that enables shoulder headspacing, might look into using the Redding #6 Competition Shellholder set to assure minimal resizing to keep headspace on shoulder.

 

[mdmp5]

Re: Belted Magnum Headspacing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Clark</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: palmik</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Clark</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: palmik</div><div class="ubbcode-body">Ok, listen... But if a 300wm case was headspacing solely off the shoulder, then the bolt would not close. That means that the belt would not be making contact with the outside rim of the chamber, and there wouldn't be enough headspace. So in reality, the most you are doing is splitting the responsibility of headspacing between the belt and the shoulder; they are both making some contact. </div></div>

I do not follow.

In my factory guns the new brass is way more than .005" from touching the shoulder and more than .005" from touching the belt.

</div></div>

If the brand new brass is not headspacing off the belt, then what is it headspacing off? </div></div>

Who says new brass is not headspacing off the belt?</div></div>

I may have misunderstood your comment about being more than .005" from the belt

 

[5R Milspec]

Re: Belted Magnum Headspacing

new brass or factory ammo will headspace off the belt eveytime.meaning that the bolt when closed and the case pushed tight into the chamber it is headspaceing off the belt.after the trigger is pulled and the round fired the case forms to the rest of the chamber.now after the first fireing the case can be rest to headspace off the shoulder.thats only if the Full Length die is set right to do so.but if not then the case headspaces of the belt again.meaning that the die was set to fare down to resize the case to headspace off the shoulder.

as said a number of times,when the case is resized to headspace off the belt it will cause the case to fail..and as Jwoolf has said annealing helps out alot to save the life of the brass.

its just a matter of what the OP wants to do.headspace off the belt or the shoulder.for me I headspace off the shoulder only when needed.I like to use the Lee collet die for my reloading till the shoulder needs to be pushed back a little.been abe to do so with great results.

again it really boils down to what floats your boat.but as said before you asked and we answered.the guys here have help many people over the years.even helped me out many times before and before I pass away they'll help out again.only time will tell.