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Neck Sizing

 
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  #22  
Old 07-17-2013, 08:31 AM
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Re: Neck Sizing

Quote:
Originally Posted by boomtube View Post
Normal neck sizing below the neck's contact with the seated bullet is meaningless.
Except that it does center the case neck more precicely on the case shoulder. Not much, but noticeable if you use the case shoulder as the front refernce when spinning cases/rounds for neck/bullet runout.

Which is why some accuracy afficianados lap the neck out of a standard full length sizing die instead of using a full length bushing die.

Quote:
Originally Posted by AZShooter View Post
The feeler gauge will set the die very close if it isn't perfect.
That's right, and lots of folks do that. But there's still the issue of controlling fired case shoulder setback. Two things make the spread of resized case headspace vary.

One's the lubricity of the case lube and how much is put on the case. The more slippery the case is going up into the full length sizing die, the less the press will spring and the case shoulder will be set back more.

The other's how long the ram's kept at the top of its stroke. I've set a dial indicator on the press and watched it slowly move the die down sizing the case a tiny bit more until it stops.

Both of these will easily cause a few thousandths spread in sized case headspace.
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  #23  
Old 07-17-2013, 10:57 AM
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Location: Mountians of SW NC, near Asheville
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Re: Neck Sizing

Bart: "Except that it does center the case neck more precicely on the case shoulder. Not much, but noticeable if you use the case shoulder as the front refernce when spinning cases/rounds for neck/bullet runout."

I haven't found that to be true and I ONLY use the shoulder as the forward reference point and the extractor groove for the rear.

Sizing necks works less on the thick/hard side so any coaxial neck offset moves that way. Neck sizing all the way to the shoulder doesn't correct that.
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  #24  
Old 07-20-2013, 04:44 PM
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Re: Neck Sizing

Quote:
Originally Posted by boomtube View Post
Normal neck sizing below the neck's contact with the seated bullet is meaningless.
Except that sizing necks all the way back to the shoulder with a full shoulder contact die ends up putting the sized neck better centered on the case shoulder.

That's why a lot folks just lap the neck out of a standard full length sizing die. And as I remember talking with Neil Jones about the neck-shoulder sizing bushings I got from him, those bushings are made so the complete neck will be sized down better centering it on the fired case shoulder that are also set back.
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  #25  
Old 07-21-2013, 07:16 AM
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Re: Neck Sizing

Quote:
Originally Posted by boomtube View Post
I ONLY use the shoulder as the forward reference point and the extractor groove for the rear.
I've checked several cases for runout between the extractor groove and the pressure ring about 2/10ths inch in front of the case head. Few have zero runout and the rest vary up to 3 or 4 thousandths. Therefore, it's my opinion that the extractor groove will be off center in the chamber by half the amount of total indicated runout to the pressure ring as the extractor's pushing the case against the chamber wall opposite its place on the bolt face when the bolt's closed.

I use the pressure ring as my rear reference as that's the part of the back end of the case that's against the chamber when the round's ready to shoot. The front of the case at the shoulder's centered in the chamber shoulder as you've mentioned and it's the front reference.
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  #26  
Old 07-21-2013, 10:56 AM
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Re: Neck Sizing

Thank you Ross for sharing your detailed experience. What do you use for a feeler gauge? And do you turn your case necks for concentricity?
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  #27  
Old 07-21-2013, 01:36 PM
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Re: Neck Sizing

Quote:
Originally Posted by boomtube View Post
We can duplicate the die set up that way but we can't precisely repeat the shoulder sizing that way. Case spring back varies by brand and production lot, ditto the normal work hardening as it's recycled.
Good point.

In my experience, this was a headache; getting full length sized case headspace controlled to a small tolerance. It varies depending on the spring of the press, how long the ram's held at the top of its stroke with the case full into the die as well as the amount/type of case lube used on the cleaned cases. I tried several cures, but only the one below worked consistangly for me.

I've got the smallest spread in sized case headspace on a RCBS Rockchucker using a 50/50 mix of STP engine oil treatment and Hoppe's No. 9 bore cleaner. After fired cases are decapped and cleaned, they're tumbled in a Thumbler's Tumbler in a foam lined coffee can with a few drops of the homemade lube sprinkled around. Tumbling 40 cases them for as long as it takes to full length size them puts on a pretty uniform amount of case lube. Sized case headspace is typically under .002"; enough for excellent accuracy and case life.

I think if one uses the right Redding competition shell holder of the right heighe, then set the sizing die such that the shell holder just bumped it, sized case headspace could be more precicely controlled. It is when I set my dies that way, but the sized case headspace is much more than .001" to .002" less than fired case headspace and accuracy suffers.
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