Tight necks

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jask
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Tight necks

Post by jask » Mon Jan 26, 2015 10:19 am

For best accuracy, what is considered the optimal neck clearance between the loaded round and the chamber neck?

Also, what is considered the best for bullet tension. .001 or .002?

I see recommendations for .002 to .003 for neck clearance. I intend to barrel my shot out short .308. I am going to get a custom reamer for 7-08 and would like to go with the tight neck. This will be my first rebarrel attempt.

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Re: Tight necks

Post by Snake » Mon Jan 26, 2015 10:37 am

JASK>>>>>>My rifle is in 7-08 with a .310 neck. I turn my necks to .011 thus allowing .002 expansion all around. I use a .304 button to size which adequately compensates for spring back. The body of my reamer is .0005-.001tighter than saami specs and generally conforms to pressure gun type specs. 260, 7-08 and 243 all have 20 degree shoulders and require turning below the juncture because of brass migration into the neck-shoulder junction and thus weird tension on the base of the projectiles. FYI the neck turning lathe shown on the 6BR (accurate shooter) is superb.

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Re: Tight necks

Post by jask » Mon Jan 26, 2015 11:07 am

Thanks for the info.

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Re: Tight necks

Post by DennisC » Mon Jan 26, 2015 11:34 am

Started out with .310nk 7-08, lapua/rem brass. Brass neck .012 x 2= .024+.284= .308 for .002 clearance.

Had reamer reground to .312 nk many years ago. Necks now turned for cleanup...end up .0115-.012 or so, total clearance ~.004-.006
I size NKs in bushing dies with .303-.307 bushings depending on lot (nk thickness) of brass accumulated through years.

I've seen no difference in accuracy and I can shoot all three days Nats (moly bullets) without carbon build up in throat area causing hard chambering/ extraction issues.
Very important what's in your head as to confidence in equipment going to the line....Used Snake's setup for years before above change....either setup will easily clean turkeys...

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Re: Tight necks

Post by Snake » Mon Jan 26, 2015 11:56 am

It goes like this .011 x 2= .022 + .284 = .306 or .02 on EACH SIDE..... otherwise by the .002 calculation there's only .001 expansion on each side :D anneal and fireform your brass

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Re: Tight necks

Post by jask » Mon Jan 26, 2015 10:33 pm

Snake, is Charles Wheaton still running a HP match in Paris?

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Re: Tight necks

Post by Jerry G » Tue Jan 27, 2015 8:28 am

What does another quarter minuete accuracy mean when you have a 6 minuete hold? We arn't shooting bench rest. :ymdevil:

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Re: Tight necks

Post by jask » Tue Jan 27, 2015 9:23 am

Jerry, it doesn't matter if you have a 10 minute hold. Any improvement in accuracy is important.

Look at what 1/4 MOA gives you on Rams. 1/4 MOA is 1.43 inches at 500 meters so if you do the math and assuming 50% of the edge shots would be within the 1/4 MOA, you have a net effective size increase of Ram height and length of 1.43 inches.

How many shooters out there would turn down an opportunity to shoot at "oversize" rams if they had the chance?

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Re: Tight necks

Post by Snake » Tue Jan 27, 2015 1:31 pm

jask---Wheaton is still around but has the infirmities of old age. He can hardly walk. Doug Mallory runs the Paris matches. As Col Townsed Whelen said ..'Only accurate rifles are interesting'..................I need an accurate rifle...i count on edge hits..actually I hope and pray for any kind :p

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Re: Tight necks

Post by Trent » Tue Jan 27, 2015 8:48 pm

The edge shot idea, while sound... may not be. With a big group size, when I break on the edge of the ram or just off the edge 50% of my shots are still going to hit, and 50% of my shots are going to miss (assuming evenly random dispersal). Imagine a pie plate taped to the edge of a ram, half on and half off (sometimes more off than on). That is the group radius. Now, humor me if you will, if I shrink my group size by half but still break in the same place... less of my bullets will hit! Technically... we need less accurate rifles! :mrgreen:

Or just break inside the animal. 8-x

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Re: Tight necks

Post by jask » Tue Jan 27, 2015 9:57 pm

Trent, OK, that blows up my first claim.

How about this.

Lets say you have 1/2 MOA accuracy. If you break all shots at 1/2 MOA inside the animal, all shots hit. If you have 1 MOA accuracy and you also break all shots at 1/2 MOA inside the animal, 25% of those shots would miss. With the more accurate rifle, you hit all 10 animals. With the less accurate rifle, you statistically miss 2.

A more simple way to look at it is a competitor with a 1/2 MOA rifle only needs to break the shot at least 1/2 MOA inside the animal. A 3/4 MOA rifle would need all shots within 3/4 MOA inside the animal. A less accurate rifle effectively reduces the size of the animal for guaranteed hits however, I like the idea of shooting at larger animals. It just makes me feel better thinking I am shooting at larger animals.

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Re: Tight necks

Post by kevinbear » Tue Jan 27, 2015 10:32 pm

jask wrote:Trent, OK, that blows up my first claim.

How about this.

Lets say you have 1/2 MOA accuracy. If you break all shots at 1/2 MOA inside the animal, all shots hit. If you have 1 MOA accuracy and you also break all shots at 1/2 MOA inside the animal, 25% of those shots would miss. With the more accurate rifle, you hit all 10 animals. With the less accurate rifle, you statistically miss 2.

A more simple way to look at it is a competitor with a 1/2 MOA rifle only needs to break the shot at least 1/2 MOA inside the animal. A 3/4 MOA rifle would need all shots within 3/4 MOA inside the animal. A less accurate rifle effectively reduces the size of the animal for guaranteed hits however, I like the idea of shooting at larger animals. It just makes me feel better thinking I am shooting at larger animals.
Interesting take on this, makes me feel better about all the work I do on cases!
Another aspect of this is when your mind tells you, hey it's ok to shoot the shot and your on an edge or in the head or whatever low probability hit "zone" your on an accurate rifle certainly doesn't hurt.
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Re: Tight necks

Post by Jerry G » Wed Jan 28, 2015 9:34 am

Draw a 10 minute circle and then draw a 1/4 minute circle with the center of the small circle on the large circle line................ That only makes the outer edge 1/8 minute larger on the radius.

1/8 minute at 500m is 0.69 inches. Not a lot to wotk with.............. Improving the hold will get you much better results. :-bd

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Re: Tight necks

Post by kevinbear » Wed Jan 28, 2015 8:39 pm

Trent said something earlier that gave me pause to think about "Or just break inside the animal", the problem is if your gun is inaccurate it's possible to break all the shots " inside the animal" and still miss some of them, all things considered accurate is better especially if you do as Jerry suggested " Improving the hold will get you much better results"-only if your gun is accurate enough to take advantage of said hold.
Jask has it right on this one, if your gun is only capable of 1 minute accuracy your essentially giving up 1/2 minute around the outside edge of the target, there is a probability factor in there somewhere and a good mathematician could figure it out. I couldn't even spell the word mathematician so I'm probably not the guy to calculate it! {thanks spellcheck!!}
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Re: Tight necks

Post by OldRanger » Thu Jan 29, 2015 8:23 am

So what I'm hearing is, since I rarely break inside the animal I want a less accurate gun. That way I have a better chance of hitting them, right?
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