Determining Neck Diameter

1. Jim1 ABNew Member

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Feb 6, 2007
I'm building a 6.5 Ruger and plan on using 7mm Dakota brass. I expect I'll have to ream or turn the necks, even more if I have to use 375 Ruger brass. From what I'm reading on a thread search for neck turning .011 for neck thickness is a good average. Reamer drawing shows the neck cut at .298 so with a bullet diameter of .264 plus a neck wall thickness of .011 a loaded case should be .275 with a .023 difference. Is there a rule of thumb on minimum for the case to expand on firing.

A little help in the procedure and equipment needed would be a great help.

Thanks in advance for the help
Jim

2. MikecrWell-Known Member

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Why do you assume that neck turning is needed?
Is the brass .017" thick?

.264 +(.017x2) = .298
A .298 reamer will likely cut ~.300

Absolutely no way should you turn to .011 and create all that clearance.

3. Winchester 69Well-Known Member

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Max brass OD (with bullet) should be considered to be chamber dia. minus clearance (usually 0.003" min.). Outside turning of the brass is usually the preferred method for reducing brass thickness and uniforming. For accuracy, most prefer a handheld tool. Reaming is good for bulk metal removal and the elimination of donuts as they form. With your specs, a neck thickness of 0.015" would be close.

It appears that your calculations do not allow for two thicknesses of neck metal.

Last edited: Mar 24, 2008
4. Jim1 ABNew Member

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Well first thanks Mikecr for correcting my oh so good math skills. I should have added two wall thickness'. da! What I'm getting at is when does it become necessary (safety factor) to neck turn. I have used 30-06 brass for a 25-06 quite often, but they were factory barrels and chambers. I've used 375 H&H for my 358 STA before I knew I could have problems but had none.

Is there a minimum for clearance???

Thanks
Jim

5. Jim1 ABNew Member

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Win 69, thanks.

As Mikecr says the reamer will probably cut .300 for a chamber. Asking the gunsmith to determine this will be a good start, yes??

.003 min. that's what I'm looking for and necks maxing out around 0.015.

Thanks again guys
Jim

6. MikecrWell-Known Member

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Asking the gunsmith what you'll end up with is right. He'll know.

My thing is minimum clearance, for minimum sizing.
As said, .003 is pretty normal and fine.

7. davewilsonWell-Known Member

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.003 min. that's what I'm looking for and necks maxing out around 0.015.

Thanks again guys

i would say you have the correct numbers for both.

8. Jim1 ABNew Member

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Thanks a lot guys. With any luck I will'nt have to do anything with the necks at all.

Jim

9. woodsWell-Known Member

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Jun 4, 2006
Hey Jim

Since you probably won't be able to buy 6.5 Ruger brass for a while (I can't find any on Midway yet) I would assume you are going to have to buy factory loads, shoot them and reload the expended brass. If that is correct, then what I would do would be to buy a box of factory loads and mic the outside neck diameter.

For example if the factory loads mic'ed .296" (and there will be some variance) then you will have some kind of idea what to ask the gunsmith to make the neck. In that case you could choose to avoid neck turning by asking for a .296" + .003" = .299" neck. That would allow you or someone else who wound up with the gun later to shoot factory. If you wanted to turn just enough to clean the necks up some then you could ask for a tighter neck.

I have a custom barreled 6.5 rem mag that has a .292" neck. I can buy Remington brass for that caliber off Midway or elsewhere and I have found that the new cases have a thick neck of between .015" to .017". So I have to turn the necks down to .0125" (.292" - .264" = .028" - .003" = .025" / 2 = .0125").

A friend liked my 6.5 rem mag and wanted me to help him in the decision making but he wanted the possibility of shooting factory ammo. So we bought a box of factory ammo and they measured .295" or less. His gun will have a .298" neck which is a good size cause I can neck turn the thicker factory cases just enough to clean them up (.298" - .264" = .034" -.003" = .031" / 2 = .0155") or he can shoot factory.