What's going on with this brass?

[Texas10]

Psteinmayer, I appreciate you're taking the time to write. I am seeing my primers are backed out 10-15 thou. They don't look particularly flatted, just backed out. Not sure what to make of that. There does not appear to be a crimp mark on the heads so they must have thought it not necessary. Maybe that is a requirement only for ammo shot from semi-autos.

Could this be due in part the result of my not cleaning all the oil out of the chamber and the brass not gripping the chamber wall enough? Not sure of the mechanics of a rimmed cartridge when it comes to primers backing out.

[Parashooter]

Several generations of American shooters have been convinced by bad information that something called "headspace" should be checked and re-checked on almost any vintage rifle. The truth is less interesting but still worth knowing.

Stripped to its essentials, with a rimmed cartridge like the .30/40, headspace is simply the distance between the face of the bolt and the back of the barrel. It's the space where the "head" (rim) of the cartridge fits when the rifle is loaded.



Since there has to be some room to allow for varying rim thickness, the headspace is normally a bit more than necessary - giving what we call "end play" or "head clearance", a little extra space so the bolt can close easily, even on the thickest rim allowed.

When a full-power cartridge is fired, a whole string of events occurs.



1. The firing pin shoves the case forward, rim against the breech.
2. The primer detonates. If it's not heavily crimped in place, it backs out, shoving the bolt and barrel as far apart as it can.
3. The thin, forward part of the case expands to fill and grip the chamber while the bullet moves out of the case and down the barrel.
4. The solid case head can't expand and grip the chamber, so it moves rearward, re-seating the primer, stretching the case walls just forward of the head, and stopping when it hits the bolt face. (If pressure is low, primers may be left protruding.)
5. If (and only if) the amount of head movement exceeds the elastic limits of the case, the cartridge separates into two pieces.

New cartridge cases can normally stretch a lot before breaking. Even with a minimum rim .054" thick and maximum "field" headspace of .074", the resultant .020" end play is well within the limits of new brass and it's very unlikely a new case will separate even if the headspace is somewhat more than the field maximum (which is pretty rare, especially in Krags.)

[Parashooter]

OK, but if one does separate we're in deep trouble, right? Not really. It seems the short "cup" left behind the break is pretty good at keeping most of the gas where it belongs. Here's a quote from Hatcher's Notebook -

". . . With good strong actions and moderate pressure loads, and especially if the shooting glasses are worn, this trouble is not particularly dangerous, but is annoying and inconvenient. Very little, if any, gas escapes to the rear, because the back end of the cartridge, which remains in the chamber, acts as a seal. In fact, it is just such short brass cups that the Germans have for years used as the breech seals in their heavy artillery . . .

"Our riflemen are used to measuring the headspace of their rifles by thousandths, and are prone to become very much alarmed if the headspace gauges two or three thousandths of an inch more than the normal maximum. This is a good safe attitude to take, but it is something like measuring cordwood with a micrometer. . ."

If you handload for a US Krag with generous headspace, there's no need to mess with bolt swapping - changing the rifle's clearances to yield longer case life. You can control cartridge end play simply by changing technique.

When you fire a new case for the first time, use an improvised spacer ahead of the rim - anything from a precision metal washer to dental floss can work to hold the the cartridge head firmly against the bolt face and eliminate or reduce stretch even if head clearance is significant. Such techniques are useful only if the rifle has excess headspace. With normal headspace, initial stretch isn't enough to worry about.



After you've fire-formed your new cases they will fill the chamber fully, stopping on the shoulder just like a rimless cartridge. If you neck size, you'll have zero "headspace". If you have to full length size, adjust the die so the cases chamber with just a bit of resistance in the last few degrees of bolt rotation. Cases fitted this way and fired with moderate loads can last for dozens of loading cycles.

[Parashooter]

See more of the same at http://www.milsurps.com/content.php?r=296-Headspace-101-for-.303-s

[butlersrangers]

'Parashooter': As always - Great explanations and graphics! Thanks.

P.S. - IIRC - A primer projecting to the rear that has maintained its rounded corners ('cup-shape' and not flattened), can be a sign of low pressure in rounds. On Firing, the primer was pushed back to take up 'free play', but, there was not enough pressure to stretch the cartridge case and force the case-head rearward against the bolt face (which would have re-seated the fired primer).

IMHO - If there is no evidence of gas leaking from or stretching primer pockets and cartridge cases are not separating, the brass is doing its job. Use the cases as fire-formed. Just trim brass as needed and Neck-Size.

[luvmy40]

I have a set of Lee dies coming and would like to do some reloading. I have about 100 rounds of NIB ammo I've collected recently at gun shows or off the shelf when I see it.

Any suggestions as to what I can expect while reloading would be greatly appreciated. :)

The Lee set does not come with a neck sizer. They(Lee)don't make a neck sizer for the 30-40 as a stock item. I assume they will custom make a die to your specs but you can get a bushing neck sizer die from HC-4D https://www.ch4d.com/products/dies/sizing/sbns

Though as others have said, I get good results just backing the full length die off a bit.

[Texas10]

Fantastic explanation, Parashooter. Best I've ever seen! And the graphics were extraordinarily well done. Thank you, thank you, thank you! The rimmed case headspace is rarely explained in detail in modern manuals. My 1949 Lee manual is better, but still...

Of the ten rounds I shot this week, 5 Remington, 5 Winchester, all ejected with primers backed out about ten thou or so, and all were flattened except the 4 Rems that I reduced the load by 3 gr. Those still had nice rounded edges.
Both the Rem and Win are loaded to full case and at least slightly compressed loads.

I am planning to hand load my neck sized only brass per Hornaday manual using 3031 or 4320 which I have in stock, and 150 gr. v-max, but not sure if I should use magnum primers.

Now, I don't want anyone to stick their necks out un-necessarily, but I would like to ask for some advice..

As I wrote above, I did reduce the loads of the first four rounds I fired, AGAINST THE ADVICE I was offered, and I wanted to explain that.

I've been hand loading for only about a year, but I've been doing it with a lot of research done beforehand, logging everything, keeping targets, x-cell spreadsheets, etc. Trying to be scientific about it and not just hap-hazard.

I've hand loaded about 2000 rounds to date and have achieved some ridiculously small groups out of my 223, which, as you probably know, is perhaps the easiest round to load.

So my question is, was I taking a big risk in reducing loads by 3 grams (typo, that should be grains) and assuming it was safe to shoot?

The results were as I expected, but perhaps that was pure luck, so feel free to ream me if I screwed the pooch on that. Might help to keep me safe and around longer so I can pester you mercilessly with more questions. ;D

[butlersrangers]

'Texas10': I think you meant to say reduced powder weight by three Grains (not Grams).

In regard to safety, I don't rightly know. I do not know what propellant was used in the old Factory Loads, that you reduced.

From what I have read over the years, DETONATIONS occur with reduced loads of slow burning powders.

IMHO - A safer course for you, would have been to dump the original powder charge, instead of reducing it, and replace it with a starting load of a known propellant, like IMR-3031, IMR-4064, or IMR-4895.

[Parashooter]

So my question is, was I taking a big risk in reducing loads by 3 grams and assuming it was safe to shoot?

If you reduce a typical .30/40 load by 3 grams (46.3 grains), you'll have no powder in the case. Be sure not to confuse grams and grains. Different systems.

You'll continue to see protruding primers until you put in enough powder to expand the case fully. With 150-grain bullets, that may require about 40 grains of 3031. Once the case is expanded to fit, neck or partial FL sizing can maintain minimal cartridge end play, eliminating primer protrusion even with lighter loads.

[Keith Herrington]

This is once fired measurement.

Your measurement is .002" shorter than what my fired brass measures. Pretty darn close. Now measure neck dia., shoulder dia. and dia. at the gas ring (near the rim where the texture of the brass changes on a fired case). Post measurements so we can compare to ours.
Keith