How much clearance needed to chamber a round?

P

piniongear

Guest
Calibers:
17 Remington
204 Ruger
6mmPPC
308

How much clearance is recommended between the chamber wall and the OD of the brass on a loaded round?
I have several rifles of the same (above listed) caliber, yet with different size chambers.

Right now I use Wilson neck dies with bushings of different sizes.
The brass is neck turned (when required) and I have been sizing the brass to have .002 total clearance. That is .001 clear all around the neck of the loaded round as it sits in the chamber.

The only 'drawback' to this is I have to mark my brass with Lot numbers and keep it separated. If it gets mixed then some rounds will not chamber in a certain rifle.

The rifles shoot well but my .002 clear is just something I pulled out of the air.
Anyone have a comment?
Thanks...... pg
 
Lots of people have dies that are only that far under, so if you are saying you're resizing and when done, the case measures 2 smaller, that's gonna work very nice. It should be pretty easy to resize the cases you mention because they are not great big magnums. Those are a little tougher to do because the bigger the case, the less die material is left once that hole is in there. Those dies tend to stretch more than ones for the cases you list above.
 
zero.

I use as close to zero as humanly possible.

IMO it's a huge mistake to make your dies only .002 over your new brass. I like a chamber that's .004 to .005 over at the base and whatever you want at the shoulder and a crush fit (zero minus-minus) for the length.

I use .002 to .001 clearance aroung the neck. Many good shooters prefer .003.....

al
 
Semi Newbie here,

But, in my opinion unless all of the various calibers you indicated above were chambered by a "competent" smith and head spaced identically using the same reamer from gun to gun (according to cartridge of course); you're stuck. I have guns that are the same caliber/cartridge and chambered by the same reamer and head spaced the same but, I choose to have each gun have it's own lot of brass and don't interchange unless absolutely necessary. I rarely do anything more than neck size, although I recently built a 6x47 Lapua that requires "bumping" the shoulders about .0015 every other loading but, I'm shooting the higher end of the load window too. The neck only has .0007 of clearance and the gun shoots in the high .002's to the low .003's consistently. I believe the rule of thumb is that brass after firing shrinks from the chamber dimension about .001 - .002 as it is heated and cooled (I could be wrong) so, if your rounds won't interchange then I would assign specific lots of brass to each gun accordingly. I shoot mine as tight as I possibly can and still get the bolt closed without breaking the bolt handle off (kidding) but, pretty tight though. Just my opinion, worth what you paid for it as the saying goes. Maybe some of the the pro's will chime in. I'm not sure if this answers the question you're asking or not but anyway................

Hope this helps,
Med.
 
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OK guys, thanks for your comments and advice.
I guess my question has been answered.
All of my rifles are factory chambered except one.

I have (3) 6PPC rifles, 2 of which are factory chambered Sakos.
The 3rd Sako 6PPC is rechambered with a Hart barrel and the work was done by Hart.
The two factory chambered 6PPCs are both .265 chambers. The bullets for these two guns will not chamber in the .262 rifle. No way.

So I keep the brass separate and only neck size. As a result the case sizes are what they are.
After firing, I assume the brass has expanded to the full dimensions of the respective rifle chamber it was fired in.
The only thing I change is with the particular bushing I decide to use in the Wilson neck die.
The bushing size I use is simply determined by the bullet diameter plus 2x the brass thickness minus .003.

Where I had to turn the brass was on the tight chambered (.262) Sako 6PPC rifle.
So the chamber size is what determines if (and how much) I have to neck turn the brass.
Then I set the ogive of the bullet just touching the lands and the accuracy is very good. This works on all 3 Sakos, as long as I keep the brass segregated.
Does that make sense?
Thanks....... pg
 
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