Case Head Separation in Mosin-Nagant.

Now we are heading into new territory, but that is what conversations do. I have a perfect example of what RevGeo is talking about. I was at the range when someone accidentally put a .300 Savage cartridge into a M/N and fired it. He said he immediately felt the recoil difference. This was a factory Remington cartridge and probably loaded really low. I looked at it, and next to a case fired in a .300 Savage, there was no noticeable difference. The distance (By eye) from the shoulder to the base on both the .300 and M/N are very close, but the body diameters are way different. I suspect if the .300 Savage had been loaded hot, the brass would have really expanded and the results would have been much different. Backing off on loads DOES make a difference in brass life.
 
...but the body diameters are way different...
Click to expand...
And therein lies the difference when "backing-off-a-few-grains" between situations

With proper cartridge case/chamber fit (i.e., MN case in MN chamber), even a moderately
-low 35,000psi load will expand the case walls enough to hold the front of the case locked/-
sealed against the chamber wall -- while stretching the unlocked case portion to the rear.

With an improper cartridge case/chamber fit (i.e., 300Sav case in MN chamber)
where there is gross disparity in dimensions, the case can never expand far/strongly
enough to firmly grip the chamber, and the case simply slides back en-toto
to the bolt face -- no stretch.
 
These winchester cases have been through about 5-6 loads
Click to expand...

By the first loading the reloader should know the length of the chamber from the shoulder to the bolt face.

There is no rule that says a reloader can not measure the length of the case after firing and again after sizing. Then there are a very few reloaders that measure the length of the case from the shoulder of the case to the case head on new, over the counter factory ammo 'JIC', that would be just in case they wanted to know the length of a case from the shoulder to the case head that would allow the bolt to close.

F. Guffey
 
Mehavey, that is not true. I stuck a 6.5 Japanese cartridge in a 6.5x55 chamber once and you better believe it expanded. It was carbon free at the neck, which was really short, and the rest was formed to the chamber. The fact that the .300 Savage case looked normal(No carbon on the neck) and proper length (By eye) tells me it was trapped between the front and back and sealed properly. Had it been loaded hot, the body diameters would have expanded. The extractor was not holding it. I picked the gun up and tapped it on the table and the case fell out. This is normal. I often took the extractor off to test fire a barrel job. Most of the time the case will fall out as you pick the rifle up.
 
It may have given a gas seal, but it did not stick to the chamber walls. If it had, the case -- driven forward by the firing pin to the limits of the extractor (if installed, or the shoulder if not) -- would have then stretched back to meet the bolt.
 
How do you explain nice round primers that protrude from the case after being fired? If the case was pushed back it would flatten/push the primer back in. It did not happen to the .300 Savage case in question, but as I stated before, it was probably trapped between the shoulder and the bolt face because the extractor could not reach the rim.
 
We may have different expectations of what "stick" should mean, but by definition, the case "sticking" to the chamber walls is the gas seal.

And with the correct case in the chamber, it takes WAY less than a "mild" 35k psi load.
 
I should know better than to get involved in a thread that is on the bottom of page 3. "The firing pin drives the case forward etc. etc..". My firing pins are killer firing pins, my firing pins crush the primer before the case, powder and bullet know their little buddy has been crushed. everyone else has firing pins with discipline, that uses an organized discipline/sequence of events.

What ever goes on in my chamber is anything but organized and or disciplined, it is violent....and fast.

Sealing the chamber: I have cases that have gas cuts up the side of the case in the body, everyone says those are cracks, they claim the cases split, and I say fantastic, the gap in my cases were gas cut.

Then there is the sealing of the chamber, if the case does not seal the chamber gas fills both sides of the case, when the pressure drops inside the case gas trapped between the case body and chamber crush the case.

I am the fan of cutting down on all that case travel.

F. Guffey
 
it takes WAY less than a "mild" 35k psi load.
Click to expand...

I was accursed in being involved in "some risky stuff", it had to do with forming cases to a chamber. ' "mild" 35k psi load ' would not form the cases from the shoulder to the bolt face of the chamber. The "risky stuff" assured me the case would form and the case would not stretch, rather than attempt discussing the methods and techniques and provoking someone I called Hodgdon, Hodgdon had a caution, forming the cases would work with no risk but the load and bullet I was using would be at or above maximum load after the cases were formed.

F. Guffey
 
The neck expanding is supposed to be the gas seal. If you get the neck area to big the case will not seal properly and the neck will be loaded with carbon back to the shoulder (And farther). Because of case varitions(Thickness) some neck dimensions of the same caliber are different so there is a proper seal.
The case sticking to the chamber walls when the gun fires and not moving is a proven fact. Would the case not then form to the chamber around the case body and to the rear, stretching the case? That did not happen.
 
How do you explain nice round primers that protrude from the case after being fired? [300SAV in NM Chamber]
Click to expand...
Normal 300SAV in 300SAV Chamber/Barrel
150 Speer FMJ/OAL: 2.6"
H4895/41.0gr
Case Water Volume: 52.5gr H2O
0.308"Groove/0.073XsectionBoreArea
50,2000psi/2,630fps

Same 300SAV load in NM Chamber/Barrel
Equivalent* Case Water Volume: 64.0gr H2O
0.312"Groove/0.0744XsectionBoreArea
33,000psi/2,400fps

As before, it will take "more that a few grains (equivalent) drop" to keep brass from
stretching, and the drop in pressure from firing a 300SAV in a Mosin-Nagant is certainly that.

*"Equivalent" Yes&No since the brass retains its shape. But once the heel of the bullet
has traveled 1/4" to clear the case mouth, the whole chamber comes into play.
 
Mo,
If you got 8 reloads out of your brass, you got good accuracy, you're not showing other signs of over-pressure, and your headspacing is good, you might simplify things by continuing the way you're doing, using good quality brass, and just drawing the line at 5 reloads. Or 6, if you prefer.

You know your Mosin is quirky, that may be one aspect of the price of doing business with it.
Denis
 
Thanks, Denis, that's what I plan to do. I plan to load 20 or so rounds when I get some more 4350, then after 6 reloads moving to 20 new cases. Because accuracy was quite good with this load. Anyway, Thanks, again.

Regards,

-Mo.
 
I went and had the headspace checked again,
Click to expand...

That is acceptable to everyone on this forum but me.

it checked out
Click to expand...

To me that statement has no value. I want to know the length of the chamber from the shoulder to the bolt face in thousandths.

You have a press, dies and cases, I suggest you practice sizing cases then learn to measure the length of the cases from the shoulder to the case head. The difficult part? Moving the shoulder forward, most accomplish this task by firing the case. Before I do that I purchase cases fired by someone else in chambers that I would consider trashy. "OR" cases fired in machine guns.

F. Guffey
 
We agree Guffey.
(Mark your calendar) ;):D

Fit to the chamber and there's no reason a medium-pressure/bolt-action/front locking-lug
case shouldn't last at least a dozen (or more) loadings.
 
"The firing pin drives the case forward etc. etc..". My firing pins are killer firing pins, my firing pins crush the primer before the case, powder and bullet know their little buddy has been crushed.
Click to expand...

This statement flies in the face of known, proven, and accepted ballistics.

Please enlighten us on how, exactly, you know that your primers are ignited before being driven forward by the firing pin? Fact is, there's NO pressure exerted by the FP on the primer until the case has been driven forward in the chamber to take up the headspace "slack".

http://www.hornady.com/ballistics-resource/internal

I can find others...but I'm sure your credentials trump Hornady's engineers.

But now we're so far off-topic, who cares.
 
Guys,
At this point I think for Mo's sake ON HIS RIFLE, just let him have his accurate load & 5 or 6 reloads. :)

I'm surprised this has gone on so long.
Denis
 
I had a Triumph 650 in England in 1975.
The thing almost killed me one day.
I never put any oil in it at all. :D
Denis
 
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