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Neck turning vs Bullet seating pressure

 
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  #1  
Old 11-24-2003, 08:04 PM
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Neck turning vs Bullet seating pressure

Hi all, I have a 300 RUM and have turned all the necks on my cases to .014 to .015. I load them with 98.0 gr of H-1000 and 165 SST. At the next reloading using the above when I went to seat the bullets, some went easy and some went hard. I don't see any pressure signs. Did I start to extrude the brass into the neck making it thicker again or is it something else.
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Old 11-24-2003, 08:15 PM
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Re: Neck turning vs Bullet seating pressure

Are you using a bushing die? Are you annealing your brass? Did you clean the inside of the necks? Is this a factory chamber or a tight neck custom chamber?
Crow Mag
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Old 11-24-2003, 08:22 PM
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Re: Neck turning vs Bullet seating pressure

Crow mag,

No die bushings, and a standard chamber. No annealing on the brass. I deburred the necks and ran a brush through the necks.
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Old 11-24-2003, 10:23 PM
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Re: Neck turning vs Bullet seating pressure

What tool are you turning the necks with and what's your process?

How many times have you loaded them after turning?

Where there variations right from the begining, after turning them?

Have you reamed the insides, or measured the thickness at the sholder/neck juncture?

How far does the bearing surface go down into the neck, is it near the juncture?

Is the seating pressure consistant, or different as you start and for the first half of the bullet being seated, and does it get tight on some near the end of the stroke?

All brass has been fired an equal number of times?

These will all give you valuable clues to where the inconsistancy lies.
My Forster will cause what might be the same problem, the K&M does not. Uneven neck thickness in this case (.001" variations)
You said .014" - .015" thick.

All mine are now turned to exactly .0124" thick. I use a bushing die and all are the same when seating. I have a digital readout SeatingForce device here that measures the peak pressure to seat bullets that I've been playing with a little but, nothing serious yet.

If you don't use an expander ball, or it expands the necks only slightly to none, neck thickness will be even more critical.

Mine are seated with near .001" neck tension, .333" before seating, and depending on the bullet, it's near .333" after seating. That's using a .331" neck bushing in the die. Cases measure .3332" after firing in the .335" chamber.
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Old 11-25-2003, 07:38 PM
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Re: Neck turning vs Bullet seating pressure

Brent,

I am turning my necks with a forester neck turning tool. I run them through a FL sizing die and then turn the necks.

I am currently working on the second time through for loading.

Yes, there were variations but not nearly as bad as they are now.

I have not reamed the insides. Why would one need to ream the case when the neck turning makes the necks the same thickness?

I don't have the right Mic to measure the thickness at shoulder neck juncture.

By the bearing surface do you mean where the bullet contacts the shoulder? If that is it, then the bearing sufrace is pretty close to being in the middle. My OAL is 3.640 with 165 SST.

As far as I can feel the seating pressure is uniform.

All the brass has been fired at least once. I am working through the second firing.

So then if you use a neck bushing do you use an undersize expander ball for decaping?

Do you think I should turn my neck thinner? I am trying to get more accuracy out of it and I know that the variations in seatng pressure don't help!

I also don't know what my chamber measures at the neck. It's factory cut but that would make a difference in the size of bushing that I need.
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Old 11-25-2003, 08:14 PM
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Re: Neck turning vs Bullet seating pressure

When using a bushing die you do not use a expander I use a .002 or .003 smaller than a loaded round for the bushing. Using a bushing die will help accuracy. I do not use a inside reamer. Baring surface is the length of surface that is touching the rifling. With a factory chamber I would just turn the necks so that you are cutting just over half of the neck you don't want to cut to much of the neck. You just want to make them uniform. Hope this helps
Crow Mag
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Old 11-26-2003, 12:38 AM
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Re: Neck turning vs Bullet seating pressure

Craig,

You first sized the cases, then neck turned them... they seated fine, and with seemingly consistant tension. You then fired these and sized them again, only this time they had uneven tension.

If this is how it happened, the only way you'd end up with this is... uneven neck thickness.

Even if you used an expander ball, the necks would not have neen sized down the same if they were varying in thickness. Spring back qualities of the brass is the reason for this. The same thing can happen if using brass that's been fired a different number of times.

If you have even neck thickness, what you'll find is, that when you fire the cases they all measure the same diameter at the neck. When you size them, same thing... all the same. When you draw them over an expander, same thing (I.D. is different in this case). Now, introduce one that varies slightly, .0005" or so and you'll be able to measure a difference in diameter. This is because the spring back is not the same between them.

Bearing surface = actual length of the bullet that measures .308" in this case, and which fully contacts the bottom of the grooves in the rifling, and also the comes in contact with the neck on the case.

Is the bullet seated so deeply the bearing surface reaches the neck/shoulder juncture? I'm not sure what the middle was that you refered to? I'm assuming a 165 SST would not reach the juncture at that length, although the 178 A-Max is about .080" into the juncture at that lenght so...

The important thing is, the bullet will get tighter at that point because it doesn't sping back as much as the neck does, the shoulder is reinforcing it so it don't. It's best not to seat that deep if you can keep from it.

If a doughnut forms on the inside there, it just gets worse. I'd recomend a neck turner from K&M with the fluted reamer mandrel, this would cure all you're problems in one swipe.

The Forster will not get you the accuracy the K&M will, I've got both and that's why I ended up getting the K&M.

If you can't control the cut to the .0001" (ten thou) you're gonna have problems. The problem with the Forester is that the case head is held in the collet and will not float on the neck mandrel, and if it's not tight on the mandrel, almost to the point it won't turn on it, it will cut one side thinner than the other... the side the neck is torqued over to when you tighten the collet on the case head. It'll do it every time, really bad if the mandrel has anything but a super tight fit to the neck.

The K&M unit will be forced away from the cutter as it rotated about the mandrel, it doesn't have this problem, as it floats on it. The back cut on the cutter forces the case tightly against the mandrel and thickness doesn't vary no matter what you spin the case with. Let the tool float in your hand tho, as most case holders won't center the case perfectly.

Ken sells a great modified ball mic, one is really necessary if you want to see the actual deviation it's producing.

I must admit tho, with the Forester, I could easily see the deviation with a .001" capable dial caliper slipped over the case neck.

If you use a K&M, you won't need the mic, trust me, it'll be within a ten thou every time, so save your money. If you're worried about clearance issues with a fitted neck, measure the loaded diameter with the caliper and that'll work perfect.

The factory neck thickness is probably beter than you can do with the Forester, and I'd never use one to turn a neck again FWIW. I messed up practically every case I ever turned with mine.

My new 338 Lapua brass was never getting touched with it for that reason!

Hope that helps some, sorry for the long bla, bla, bla... [img]images/icons/grin.gif[/img]
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