Magnum Question

N

Nathan

New member
I saw another post stating that the magnums can be run in double rifles or bolt actions with equal ease.

This made me think of a couple questions.

1) Are case and chamber tolerances tight enough on the belt to hold the case rock solid and aligned to the bore center? Both in length and diameter? It should be the best spot on the case to align to the chamber because it has the smallest changes through sizing and shooting.

2) People complain about magnums thinning due to excessive sizing, but how is this possible? If truly held by the belt, this thin neck/shoulder should be blowing forward.

3) The belt is/was designed for reliability…it controls the critical primer impact position. Is there published test data showing this? I have seen these issues, but always when caseforming.
 
To point #2, it head spaces on the belt, or rather the belt keeps it from going into the chamber too far instead of the shoulder. To me this would mean the shoulder will be held back from contacting the chamber when struck by the firing pin. Which would cause the shoulder and neck to blow forward to fill the chamber and cause more case growth.

However depending on how you size im sure a lot of that can be mitigated to a reasonable degree.

With that being said, im no expert and have not reloaded belted cartridges. But i did some research when i was looking into getting one and it seemed like more trouble than it was worth for me personally.
 
3) The belt is/was designed for reliability…it controls the critical primer impact position. Is there published test data showing this? I have seen these issues, but always when caseforming.
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I do believe that the first cartridge with a belt was the Holland and Holland .300. Added for headspacing purposes due to the H&H .300's long tapered case, sans shoulder. It was added for headspacing, nothing more, nothing less.
https://en.wikipedia.org/wiki/Belted_magnum
 
I guess I’m saying that if the belt fit to chamber was tight axially, then the case head wouldn’t move, thus blowing the shoulders forward. Unfortunately, this doesn’t happen. I believe there must be some kind of dimensional issue.
 
All new belted cases expand to chamber limits when first fired then shrinks back a little bit .

Compare a new case outside dimensions to its first fired dimensions.

Resize the case then compare them to the other two.

Very few, if any, case heads are touching bolt face when fired. Extractors don't hold case heads against the bolt face.
 
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I do believe that the first cartridge with a belt was the Holland and Holland .300
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Close, but not quite correct. The first one was the .375 H&H, introduced in 1912. The .300 H&H was introduced in 1920.

The .375 H&H not only introduced the belt, but also "borrowed" the term "Magnum" from the wine industry, where it was used to designate a larger than standard bottle.

The belt was created to essentially "split the difference" between rimmed and rimless cases. It gave sufficiently acceptable headspacing in double rifles, AND worked through bolt action magazine rifles easier and without the drawbacks of actual rimmed cases.

The belt was not done for accuracy, it was done for positive function. Remember both the era and the intended use. The long sloping cases, with long sloping shoulders were made for use in Africa, and particularly in double rifles, which don't have powerful primary extraction.

Also look at the pressures of these original rounds. By today's standards, they are not high pressure rounds. Again, this was intentional. Long gentle slope and relatively low pressure reduced the chances of a case getting stuck. This is something important when you're hunting somewhere equatorial high temps are the norm, and also VERY important when your target is an angry water buffalo or elephant at short range.
 
The belted cartridge, first seen in the obscure 1905 .400-.375 Hollands, really popularized in the 1912 .375 H&H Belted Magnum and the 1925 .30 Super (.300 H&H Magnum) was developed for use in bolt action rifles that are difficult to get to feed the hitherto standard rimmed round.

Double express and falling block single shot safari rifles were typically chambered in the rimmed (flanged) version of these rounds.

Later, trick extractors were developed for rimless cartridges in doubles and singles, and they have necessarily been adapted for belted rounds because rims are out of style and the ammunition hardly to be had.

Bart is talking target rifles, Hollands makes hunting rifles and a little extra expansion into a roomy chamber is not such a problem.
 
What is headspacing? Isn’t it holding the case tight enough to the bolt face for consistent reliable ignition?
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That's part of it. And the primary intent.

headspace is the measurement from the part of the barrel or chamber that prevents further forward movement of the cartridge, to the bolt face, when the bolt is fully shut.

Originally it was the "space" in the gun where the cartridge case head fit. Originally, this meant the case rim, since all cases were rimmed at the time. Later on, with rimless, bottlenecked, and belted designs the measurement point changed, but the principle remains.
 
I do believe that the first cartridge with a belt was the Holland and Holland .300
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Close, but not quite correct. The first one was the .375 H&H
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Also close, but not correct. The first belted case was the 400/375 Belted Nitro in 1905. Useless trivia.
Why doesn’t the belt hold it against the bolt face?
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Tolerances are close, but you have to allow for min/max chamber dimensions and min/max headspace dimensions. Most factory loaded cases will are about .005" under minimum chamber dimensions to allow for fouling, heat expansion, etc. Once fired, the case expands to seal the chamber. The belt, on the other hand, does not expand under normal pressures. After the pressure drops, the case walls rebound so it can be released from the chamber.
People complain about magnums thinning due to excessive sizing, but how is this possible? If truly held by the belt, this thin neck/shoulder should be blowing forward
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All bottleneck cases thin in front of the web when you resize them. When you resize a case, the brass gets moved from the lowest point on the case that the resizing die reaches, which is just ahead of the belt. This is why non-belted cases thin ahead of the web and belted magnum cases thin in front of the belt. This is called "drawing", and is the same idea behind the process used to form the cases in the first place.
 
Shadow 9MM said, "With that being said, im no expert and have not reloaded belted cartridges. But i did some research when i was looking into getting one and it seemed like more trouble than it was worth for me personally."

It really isn't all that complicated The following is how I set up my resizing die and it works just fine with standard bottle neck cartridge and magnums as wee. What you're doing is ignoring the belt completely. For all practical purposes it no longer exists. Once the die is set up you now headspace o the shoulder just like regular bottle neck cartridges.

This is how I set up my sizing die for bottleneck cartridges.

1. Take a once fired factory round and blacken the neck and shoulders with a Magic Marker or Sharpee pen. Some people like to smoke the neck and shoulder, but I find the Magic Marker/Sharpee pen a bit better.

2. Carefully lubricate the case.

3. Loosen the lock ring on the sizing die and back off about two turns from when the die is set to touch the shell holder.

4. Size the case. Note where the marks are on the case and turn the die down about a half a turn and size again. Turn down some more, and resize again. What you are looking for is the marks on the blackening just touching the shoulder.

5. Clean the lube from the case and try it in the rifle. It may chamber just a bit on the snug side. If so, turn the die down ever so slightly, lube and size again. Wipe off the lube and try in the rifle. If it slides in as easily as a factory round, you should be good to go. If not, usually one more very slight adjustment should fix the problem.

6. Tighten the locking ring for the die and you're done. You have just set your sizing die up for a custom fit to your specific rifle, rather than a generic one size fits all guns. :cool:

Paul B.
 
All bottleneck cases thin in front of the web when you resize them. When you resize a case, the brass gets moved from the lowest point on the case that the resizing die reaches, which is just ahead of the belt. This is why non-belted cases thin ahead of the web and belted magnum cases thin in front of the belt. This is called "drawing", and is the same idea behind the process used to form the cases in the first place.
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Totally get that, but that applies to chambers headspacing on the shoulder….because the case expands and grips the chamber everywhere but the thick area just in front of the head, so it stretches back to the bolt face. This thins the stretching area.

A properly fit magnum belt should fit tight (<0.001” axial slop) when the case fires everything should expand out, but the case head would be trapped to the bolt face and belt with tight chamber clearance. Therefore sides would stick to chambers forcing the shoulder forward and shorten necks.

Doesn’t really happened, does it. I contend Someone has monkeyed with the dwg so it works like normal cartridges. Thoughts?
 
Thoughts?
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I have a few, beginning with practicality. IF you're going to set your standards based on finely fitted tuned match class rifles that require handcrafted ammunition, that's fine. Just don't apply that to the real world and the overwhelming majority of rifles, ammo, and shooters.

The gunmakers "bread & butter" belted magnums are sporting rifles, nearly all intended for big game hunting. Factory ammo is ALWAYS just slightly under the minimum chamber specs. This is so it fits, and fits in everything.

And, that is the point. Accuracy good enough to do the desired job, and reliability. The fellow who misses a lifetime trophy, because his min spec rifle wouldn't chamber the ammo he got, when he needed it to, isn't going to say "gee, well, that's what I get for wanting a rifle that shoots teeny groups with custom tailored ammo", what he's going to remember (and for the rest of his life) is how he missed the opportunity -and the money he paid to get that opportunity- because the #@$#^%$&@$# RIFLE JAMMED, and DIDN'T WORK!! And he's going to tell everyone he knows that's why! AND, its not EVER going to be HIS fault, either!!!!

Same thing for the guy who has a life changing up close and personal encounter with a dangerous animal, and finds that his second shot isn't happening because the first one is stuck in the chamber....things like that are concerns of gun and ammo makers.

Next thought is the simple one few people bother to even consider, and that is that neither our rifles, nor our ammo is designed with the life of reloaded cases being the top priority.

Again, you can build a rifle for that, but commercial hunting rifles aren't. Nor are military arms or sporting arms derived from those designs.

Some are much more "reloader friendly" than others, but none of them is made with the idea of maximum reuse of fired brass as a high priority.

We are focused on that, because we are reloaders. Gunmakers are focused on producing a funtional, reliable product that gets the job done. If we can get multiple reloads using their gun, fine. If not, its really machts nichts to them.

Lastly (for now:rolleyes:) headspacing on the shoulder vs on the belt does not apply to EVERY belted magnum case. Nearly all, yes, but not every single one. One of my belted magnums doesn't have a shoulder to headspace on.

Care to guess which one it is?
 
A properly fit magnum belt should fit tight (<0.001” axial slop) when the case fires everything should expand out, but the case head would be trapped to the bolt face and belt with tight chamber clearance.
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Doesn’t really happened, does it.
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Nope. Case head tolerances are still about .005" under minimum, so the case flops around in the chamber a bit. If it were as close as you are describing, if the cartridges got hot, or the chamber got fouled by powder residue, the breech wouldn't close.
headspacing on the shoulder vs on the belt does not apply to EVERY belted magnum case
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Sure, 458 Win does not have a shoulder, but 375 H&H doesn't realy have a shoulder either, that shallow angled shoulder is the main reason for the belt. The 375 Flanged had a rim for headspacing, and the 375 H&H's belt serves that purpose. I have shot a 375 H&H for decades, and was never able to make it headspace on the shoulder because it causes feeding issues. Most belted mags, sure, but I'm not sure about headspacing the 375 H&H on the shoulder.
 
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Yes, its the .458 Win Mag.

The .375H&H does have a shoulder, but you're right, not much of one, and not likely to be enough for positive headspacing, hence, the belt.

Fortunately, the belt works just fine for that.

kind of like the "semi rim" pistol cases Browning developed. Again, remember the era he was working in.

Browning's .25, .32. and .38 auto pistol rounds are all "semi rimmed" having a very small rim projecting beyond the case body. Enough to reliably headspace the rounds. At the time he designed them, Browning wasn't convinced rounds could be reliably headspaced on the case mouth, so he added the tiny "semi-rim" to be sure. When the success of the rimless 9mm Luger round proved the concept would work, Browning dropped the semi-rim feature from the later rounds he designed, the .45ACP, and the .380ACP.

So, while the belt does work for headspacing the round, its not a requirement, just a convenient thing that became the defining characteristic of "Magnum" rifle rounds for a few generations.

I might be able to headspace my Ruger No.1 .375H&H on the shoulder, but I'm not at all inclined to try.

I certainly could set up my .350 Rem Mag to headspace off the shoulder, but again, I'm not inclined to try. Works just fine off the belt, and I'm not concerned with case life, I don't shoot it much, have a couple hundred brass and if I happened to use them up during my remaining years, I can form cases from other commonly available belted magnums.

Its a bit of history and nostagia today, note the modern generations of magnums, both very large and short & fat cases without belts.

Because A) it works, and B) a century of popularity, the belted magnum isn't going away anytime soon, but designers of new stuff have pretty much moved on....
 
As Scorch said, a typical belted chamber will offer about .005 head clearance at the breech face when the belt stops the cartridge from moving forward.

The firing pin strike will drive the case forward till the belt stops it.

The brass is thinner forward, Thickest toward the case web.

So,at ignition,pressure rises. Brass near the case neck,thinner, expands first.

"Obturates" Beginning forward, the expanded brass grips the chamber wall.
As long as pressure is high,it does not let go. It grips essentially the full depth of the chamber that is within the barrel.

Now consider the brass between the chamber mouth and the breech.You see, the pressure will force the case head to the breech face,about .005. And the brass from approximately the chamber mouth to the breech must stretch .005. The stretch will occur at the least resistance, And the brass will thin.

This is how we get a stretch ring.

This will take you to a "Varmint Al" page. Its a little treasure.

http://www.varmintal.com/a243z.htm

If you scroll down you will see a Finite Element Analysis of a .243 case going through a simulated pressure cycle animation. Its near the bottom of the page. There is text referring to "Rough chamber"

The animation will help you visualize what I described. Al was a LOT smarter than I am.
 
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As Scorch said, a typical belted chamber will offer about .005 head clearance at the breech face when the belt stops the cartridge from moving forward.
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….and this is the key point. I wonder if that was reduced to about 0.002”, if guns and brass could be made!
 
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