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Headspace question

 
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  #8  
Old 06-07-2008, 12:59 PM
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Headspace question

As suggested I bought a go gauge and recieved it two days ago. First, I took the extractor and fire pin of the blolt, then I put the go gauge in the chamber and push the bolt on it. I couldn't close the bolt. Remember that I told you that I could put in some loaded factory ammunition in the chamber and close the bolt. Some were rubbing but they all fit in.

When I made the order to Brownell I also ordered some lapping coumpound. I then decided to lap the locking lugs of my bolt. I lapped for 3 of 4 sequences and trying the go gauge between each and suddenly the go gauge went in. I then put a 2 thousand of an inch shim on the back of the go gauge and try it again. I could not close the bolt on it. I quess, I still have a tight chamber.

Now I have to go to the range and fire that baby.

Thanks for your support guys,
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  #9  
Old 06-07-2008, 08:10 PM
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Perfect !!!!!!

J E Custom
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  #10  
Old 06-20-2008, 02:24 PM
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Quote:
Originally Posted by relabbe View Post
I just put a new 300 win mag barrel on my 700 remington long action. I have a gunsmith book that states that the go gauge will fit if there is .220 inches. I used a new bullet and a shim on it back to measure my head space and I have about .218 inch of headspace. I cycled the rest of the my bullets in my gun and they all cycle nicely. Do I still need that .002 inch missing? If I need them I guess I should be lapping the lugs on my bolt.

What do you think? any advice...

Thanks,
Call David Kiff, owner of Pacific Tool and Gauge.

28 bucks for a Go gauge.

My process when hanging a tube on an action.

Strip the bolt of anything that has a spring or might alter a measurement. (fire control, extractor, ejector being the top three things to peel off the thing)

Drop in your go gauge.

Hopefully the bolt closes freely.

Now, get yourself some .001" thick Starret shim stock and cut it into little tiny postage stamp shaped pieces that fit into the bolt face. A dab of grease will keep them from falling out.

Start stacking shim stock until the bolt just "sticks" as you attempt to close.

You now know how far past minimum SAMMI spec your HS is. (PTG GO gauges are minimum SAMMI spec unless ordered otherwise)

The term I'd use when at Nesika was "GO +.001" or .002". . . (what ever it ended up at) for the documentation on all the guns my department built.

This is useful long term in case an accident ever occurred (like a grenaded case for instance) You can repeat the test and know if the lugs were peened or if the chamber was bulged/stretched somehow.

Good luck and keep em centered.


EDIT: Sorry, jumped the gun. Sounds like you got it licked. Very cool.

Hope she works!
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  #11  
Old 06-18-2012, 10:46 AM
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Location: Remington County, PA
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Re: Headspace question

Quote:
Originally Posted by NesikaChad View Post
The term I'd use when at Nesika was "GO +.001" or .002". . . (what ever it ended up at)

If accuracy (among other reasons for eliminating ANY extra head space)) is top priority, wouldn't "GO + .000" be the most desirable result that could possibly be achieved, while still remaining within the sammi spec?

I already know the answer to that would be "yes". If all of your guns came up to that exact number, I suppose that would put you in the position of being completely "golden".

BEYOND SAAMI: Now this does stray a bit over-the-line, as far as the topic (as well as the spec) goes, but since the goal of the sammi spec is to assure universal interchangeability within a specific round, I am considering going out-of-spec on my next build.

The scenario is that there are only 2 manufacturers of the brass, including factory loaded ammo. The firearm will be expected to chamber ONLY fresh brass (including factory loaded), and brass that has been fired out of itself. But whether or not it will chamber brass that has been fired (and thereby stretched) out of another gun, is a "don't really give a damn" situation, because it is a situation that is planned on being avoided. In that respect, you can consider it to be a "custom" build.

With that in mind, my plan is to purchase at 50 rounds of each man's new brass, and set HS for +.000 on the longest case found, among the 100 purchased. That will likely put the HS at a "GO - .00x" number, meaning it would be outside of the sammi spec. Now I know that anyone's first thought (including my own) when they hear "out of spec", is "no good". But, the OOS would be on the "good" side. Among the many advantages I see, would be highest possible accuracy attainable, absolute minimal stretching of the brass, best possible gas seal, etc. And the ONLY disadvantage (that I can think of) would be that brass fired out of other guns MAY be too tight. But like already said, that is a non-issue for me.

Now granted, if I was "smithing" a gun for somebody else, or the public in general, I would NOT stray outside of the SAMMI specs, for obvious liability reasons. Speaking of which, I better also add the disclaimer that "in no way, shape, or form, am I suggesting that anyone else try this (at home, or otherwise).

Now that that's out of way, for the custom situation mentioned, can anyone (preferably experienced smiths), come up with any legitimate reason to avoid setting the HS via the procedure that I have outlined?
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  #12  
Old 06-19-2012, 12:34 AM
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Re: Headspace question

The thing you run into with sub min headspace is your sizing die may not be capable of bumping the shoulder unless you trim a bit off it.
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  #13  
Old 06-19-2012, 12:20 PM
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Re: Headspace question

That IS a point that I need to think about, considering that the sizing die WOULD be made to the "GO + .000" spec, right?

Since I'd like to avoid altering the die, I see 2 options. One would be to ease up on the HS, allowing the brass to grow enough to completely fill out the die. But that would wipe out any advantage that would be sought from going to a "GO -minus" number, sending everything right back to square 1.

Short of "shortening" the sizing die, the only saving grace that I can picture for maintaining the fresh brass's less-than-SAAMI length would be to utilize the camber of the rifle itself to perform the length (to datum line) sizing procedure on the cases, by means of fire-forming. But I'm not sure how reliable that would be, in practice.

I'm going to have to decide on exactly how far I would be willing to lower the "bar". I'm not really sure exactly how short of the sammi minimum factory brass usually is, but I'm thinking -2 to -3 would be fine, and MAYBE -4 if the brass from the 2 mans (rem & noz) comes up very consistent at 4 under. I would not want to go any more than that though.

But it now appears that I am coming full-circle, as I might as well just go +0, let the first shot stretch the brass out once, to the "standard" size, and leave it at that.

How short of saami does fresh brass typically run?
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  #14  
Old 06-19-2012, 12:35 PM
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Re: Headspace question

I have measured factory ammo or brass is usually anywhere from .008" to .012" short in my zero headspece chambers. Just go to zero to .0005" over is where I like mine. Your first firing will blow it out to your chamber size and then go from there. Setting your sizing die firmly on the shell holder will get you very close. Even with an overspec long chamber you can get good brass life and great accuracy by neck sizing and only bumpng the should the amount needed to keep the bolt closing easy.


Something to keep in mind, Headspace is only a very small component in rifle accuracy. Consistant neck tension, even powder charges, bullet seating depth and concentricity are far more important than headspace.
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