bigngreen
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Many action without spring and plunger ejection!
Brass Separation Above Belt
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bigedp51
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What does the firing pin do when it hits the primer?
It pushes the case forward until the shoulder of the case contacts the chambers shoulder, then the cartridge goes bang. The rear of the case then stretches to meet the bolt face, the distance it can stretch is your head clearance.
On a 338 Winchester, .00025" in the freebore equals ~ .001" at the base.
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bigngreen
Well-Known Member
What does the firing pin do when it hits the primer?
It pushes the case forward until the shoulder of the case contacts the chambers shoulder, then the cartridge goes bang. The rear of the case then stretches to meet the bolt face, the distance it can stretch is your head clearance.
Ya, but the firing pin was not in the conversation yet but we were getting there.
The CAD sketch I just did is showing closer to .005" off center at the base. So no, I don't think I will be relying on the free bore to center my cartridge with the bore.
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I would like to see that sketch. Can you post it?
Great discussion. I had this same problem a few year ago on a new build with head separation on the first firing. I identified a slight headspace problem but it was being complicated by a rough chamber finish causing heavy brass scaring. I believe is was preventing the brass from being able to slide back when expanding on firing. I did some light chamber honing with 1000 grit to lightly smooth the rough reamer marks and it has never split another case and been a great shooter ever since.
Now I'm not claiming to know it all or even close, but what I'm looking at is that by full length sizing and relying on the free bore for alignment it is allowing about 3 times as much misalignment as a fire formed/neck sized case. Granted, there are probably factors that I'm overlooking and this has little to do with headspace, but I plan on sticking with neck sizing and relying on the fireformed case for alignment to the bore.
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bigedp51
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So what happens when your neck sized only case warps and becomes banana shaped with the base of the case tilted and no longer 90 degrees to the axis of the bore.
Full length resizing prevents the case from misaligning the bullet in the throat.
Have you ever measured the body of the case for concentricity after it has been fired?
If you had you would see egg shaped cases because the case was thinner on one side and expanded more.
We can argue about the merits of neck sizing vs full length resizing all day long. "BUT" it boils down to the quality of your brass, the size of your chamber and if the case is distorted when fired.
And as it has been pointed out even benchrest shooters are now are full length resizing. Meaning they found out full length resizing creates a more uniform cartridge and it is more accurate.
"BUT" the best part of reloading is the person pulling the press handle decides how to do it. And that is all that matters as long as the person pulling the press handle is happy......even if he is wrong.
bigedp51
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We have also found out that the cause of the OPs case head separations was caused by a shade tree mechanic gunsmith.
And below is the cheap bastards headspace gauge to check your rifles headspace. (head clearance)
Take a new unfired case and measure its length from case mouth to the base of the case and write it down.
Now take a fired spent primer and just using your fingers start the spent primer into the primer pocket.
Now slowly chamber this case and and let the bolt face seat the primer and extract the case.
Now measure the case again from the case mouth to the top of the primer and write it down.
Now subtract the first case measurement from the second and this will be your head clearance. Meaning the air space between the rear of the case and the bolt face and the distance the case can stretch when fired. And on a rimmed case if you add the rim thickness you would have the actual headspace measurement.
And if you do not have a Hornady cartridge case headspace gauge you can also use this method to check your resized cases shoulder bump.
And below is the cheap bastards headspace gauge to check your rifles headspace. (head clearance)
Take a new unfired case and measure its length from case mouth to the base of the case and write it down.
Now take a fired spent primer and just using your fingers start the spent primer into the primer pocket.
Now slowly chamber this case and and let the bolt face seat the primer and extract the case.
Now measure the case again from the case mouth to the top of the primer and write it down.
Now subtract the first case measurement from the second and this will be your head clearance. Meaning the air space between the rear of the case and the bolt face and the distance the case can stretch when fired. And on a rimmed case if you add the rim thickness you would have the actual headspace measurement.
And if you do not have a Hornady cartridge case headspace gauge you can also use this method to check your resized cases shoulder bump.
There isn't enough numbers on that picture for it to mean anything to me.
tom m.
Well-Known Member
Guys, my sole passion is group shooting at long range. This is why 1k benchrest has been the hobby that has "stuck". I LOVE testing this stuff more than the actual match shooting, it is what is fun for me. TRUST me, this has been tested every which way... If you can dream it up, I've tested it. I've put about 40,000 rounds on paper at 1k since 2008, and attempt to learn from each one. Here's where I'm at on the subject...
I would give up an organ if I knew it would make me shoot smaller. I full length size because it shoots smaller.
I've never worn out the brass for a barrel before the barrel was toast.
Tom
. I've put about 40,000 rounds on paper at 1k since 2008, and attempt to learn from each one. Here's where I'm at on the subject...I would give up an organ if I knew it would make me shoot smaller. I full length size because it shoots smaller.
I've never worn out the brass for a barrel before the barrel was toast.
Tom
