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Excessive Headspace!

 
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  #15  
Old 12-17-2009, 05:51 PM
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Join Date: Jan 2007
Location: South Dakota
Posts: 753
Re: Excessive Headspace!

I'll share a story/experience. Take from it what you will.

I built a big heavy 6mm-284 once. It had all the high dollar stuff so I expected it to hammer.

It was initially a lemon. Just like lightening, it never struck twice in the same spot. . .

After considerable head scratching and fussing it was pointed out to me by one of my employees that the headspace was a "red one" on the tight side. The barrel was fluted and during final assy I had to give it an extra grunt to get the flutes timed up right. This was enough to cause a slight interference when rotating the bolt into battery on a loaded chamber.

We pulled the barrel, squeaked the chamber a smidge and put it all back together and it began splitting hairs on paper right away. I had a really, really, really hard time accepting that's all it was but it was the only thing that we changed so it was/is tough to argue with. I've made it a point since then to ensure the cartridge has enough room to sit "tension free" in the chamber ever since and this particular demon has never surfaced again.

Take from that what you will.

cheers,

Chad
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Chad Dixon
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  #16  
Old 12-17-2009, 07:57 PM
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Join Date: Dec 2007
Location: Youngsville, NC
Posts: 391
Re: Excessive Headspace!

Head Space is exactly that.

1. On a bottle necked rimless case it is a measurement from the "Datum line to the face of the case head."

2. On Belted Magnum cases it is the distance from the front of the belt to the face of the case head.

3. On Rimmed cases it is the distance from the fron of the rim to the back of the rim or case head face.

Simply understanding that there has to be a little space between the chamber and the cartridge or it want chamber. As stated pristine target rifles can have tighter chambers. Hunting rifles are generally built a little looser to prevent dirst, dust, unspent powder residue from keeping the bolt from closing.

SAAMI "Small Arms and Ammunition Manufactures Institute" are the industry standard. There secs insure that all factory rifles will function with factory ammunition. The allowable varible in chamber and ammunition is .0035"

As previously stated a little extra head space alone is not very dangerous. We all know the case will fire form to the chamber. The danger comes in to reloading case that are fired in a gun with excessive head space. Every time one reloads a fired case from a rifle with excessive head space, it is bumping back the shoulder if the case is going bacl to SAAMI Spec. Repeated shoulder bump allows the case to stretch and begin thinning in the web area. After repeated firings and reloadings the case head will seperate. This may or may not cause a catustrophic firearm failure.

I am sure I have just confused you even more. I don't think I can be expained it any better. Wayne Van Zoll does a real good job in the later edition of Frank de Harts book abut bolt actions rifles.

Nat Lambeth
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  #17  
Old 12-18-2009, 12:22 AM
KDB KDB is offline
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Join Date: Jun 2009
Location: Arkansas Delta
Posts: 94
Re: Excessive Headspace!

I appreciate the education. I think that I have it squared away now. Thanks
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