halfmoanut
Silver $$ Contributor
Necks need to be turned to ???? Per side. What is the formula. .262 neck chamber, bullets .2435 pressure ring. Using .256 .257 bushing . What do the necks get turned to?
Formula for loaded round chamber clearance
- Thread starter halfmoanut
- Start date
jimmymac
Jim McGregor
For the neck tension formula, you have to run a case through your sizing die with whatever bushing you choose and measure the OD of the neck prior to seating a bullet.
For the example above, lets say you are using a .256 bushing. You run a case through your sizing die then measure the neck OD of the case with a micrometer. Lets say it measures out at .2555 after sizing.
You seat a bullet and the neck OD of the finished round comes out to .2595. You then take:
.2595 - .2555 = .004, so your neck tension in this example is .004. Does that help you?
As a side note in regards to neck wall thickness, you don't have to use .0080. You can use a thicker wall thickness like .0085, but just be aware that things can get tight in a hurry between your chamber and your case neck.
Run the math for yourself, but make sure you measure everything with the appropriate micrometer for the job. This isn't a job for a caliper.
For the example above, lets say you are using a .256 bushing. You run a case through your sizing die then measure the neck OD of the case with a micrometer. Lets say it measures out at .2555 after sizing.
You seat a bullet and the neck OD of the finished round comes out to .2595. You then take:
.2595 - .2555 = .004, so your neck tension in this example is .004. Does that help you?
As a side note in regards to neck wall thickness, you don't have to use .0080. You can use a thicker wall thickness like .0085, but just be aware that things can get tight in a hurry between your chamber and your case neck.
Run the math for yourself, but make sure you measure everything with the appropriate micrometer for the job. This isn't a job for a caliper.
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The formula is chamber diameter minus the clearance you wish to start at. So lets say you start at .003" clearance. Subtract .003" from .262" and you get .259". Then subtract the bullet diameter .2435" from .259"=.0155" or 16 thousandths divided by two is a neck turn thickness of .008" for a loaded diameter of .259" and a sizing die bushing of .257". I always do just enough clearance to fireform and after fireforming twice I make a final cut of .001-.002". It seems fireform sometimes will make brass flow more to one side of the neck or the other and the final cut cleans up this runout. The amount of final neck clearance will be determined by how much bullet grip I have after firing. If you can seat a bullet in a case without sizing after firing, you don't have enough clearance in my opinion. Brass springback will determine this and every lot or brand will be different. I have however seen many competition loads that never get sized!
Excuse me if I am missing your point but did you mean "If you CAN'T seat a bullet in a case without sizing......."
It's can not can't. Brass springback figures into the equation but if you still have enough grip where you can seat a bullet without sizing the neck then you don't have enough clearance to release the bullet cleanly. And if you can't seat a bullet in the fired case, you really have a problem!!
Thanks, what I read was "If you can enter a bullet not what you actually said seat a bullet. My mistake, thanks.
I'm confused. Doesn't that make .003" clearance only opposite the side of the case neck that's touching the chamber neck?
Is "clearance" the even space all around the case neck to the chamber neck? If so, then to have .003" all around, you have to subtract .006" from .262" which is .256".
Subtracting .003" from .262" makes the bulleted case neck have .0015" clearance all around it when centered in the chamber neck. The diameter difference is .003"
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If you say so. That's different than I was taught and remember. Maybe I just learned something. Thanks.
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It's only as complicated as you would like to make it, LOL! But it is simple math'th'th!!! I r not a math major,
! You have your interpretation and I have mine. Go have a nice day!
dmoran
Donovan Moran
+1... that is how I know it, as do must everyone I converse with.
Donovan
Someoldguy
You guys need to knock it off. My ribs are gonna be sore for a month!
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