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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2008 at 03:49
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When outside neck turning one has to decide on how much material to cut away. This decision can be based on several factors:
To achieve a given case wall thickness ie .0013 inches.
To achieve concentricity, thereby only cutting away the high points only.
To achieve a tight fit in the chamber.
 
The question is this: What is the correct choice. If one decides on a given wall thickness it may give the correct grip pressure on the bullet. The downside is that the case neck  may be undersized sized and there is a large amount of play between the chamber wall and the case neck.
 
What is best, to minimize the chamber and case neck play, or to achieve a given case wall thickness. What is a good wall thickness? .0013, .0014 or what???
 
Any help, comments appreciated.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2008 at 09:28
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outside neck trimming is a remedy, to correct some of the problems you have mentioned, rarely will the soln. to one be the over all cure. bench rest turning has the static conditions of perfect chamber, throat, etc., so the neck thickness can control tension--rarely the case in hunting rifles, and never the case in semi-autos. on the other hand, many ar15 have nato shoulders and throats that get blown forward, but set back by .223 dies, somethimes this is corrected, somethimes the brass is too thick, and the case neck tension deforms the bullet on seating and needs thinning eg. wsm .223.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2008 at 09:34
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Thanks Dale.
So if the chamber is large as in normal mass produced rifles, would it be best to trimm as little as possible to have thicker brass at the neck? I am thinking that the thicker brass would give longer case life.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2008 at 12:02
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the problem I've encountered is ellisoidial throats caused by wobble reamers and or worn out reamers. The neck thickness and length is increased each time the case is pulled out of the die and the brass flows up. neck splits are usually due to small scratches in the neck caused by dirty dies. case and neck life is a function of how hot you load, thinner necks hold the bullet just as well (in most cases, literally and figuratively) but are not moulded to the shape of the bad case neck. one of the reasons reduced loads usually show better accuracy than max. loads. some of my 308 cases have been reloaded so many times the caliber and writing on base are smashed beyond readabillity.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/21/2008 at 22:38
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Dale it sounds like you get all your brass has to offer. To each his own, but for consistant and reliable loading we limit loading brass to 10 loads and then scrap it. Like you noted hotter loads shorten case life but we rarely load anything hot because most of the time we see accuracy suffer. By the 3rd load we start seeing need to trim for length and do so to keep everything in spec. By the 9th or 10th load the necks are getting pretty thin and are subject to split if pushed much farther. Atleast thats my experience. I suppose the method of prep and cleaning will have alot to do with case life as well.
8, I have always felt that keeping all components as close to identical as possible provides the best possible accuracy, case length included. Neck thickness is difficult to control and I think less of a factor untill it is to the point of failure. But also like Dale mentioned, throat issues will always effect case performance and longevity.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/22/2008 at 02:20
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Thanks for your comments. Much appreciated. I will do less neck turning in future. Just take off the high spots and try to keep/maintain max case thickness on the necks.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/22/2008 at 17:30
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Wouter, in my humble opinion, neck turning is a colossal waste of time in a factory hunting rifle, and I wouldn't bother with it.  Target rifle -- yes; Factory rifle with open tolerance chamber -- NO.  Neck turning is beneficial if you are either handloading for a benchrest rifle with a tight neck chamber or you are reducing neck thickness and lack of concentricity after resizing a case to a smaller caliber.  Neck turning is also useful if your cases have grossly inconsistent neck thicknesses.  As for proper thickness, usually, I've found that between 0.010" and 0.012" is the correct thickness.  I turn to 0.010" thickness for my 0.265" chamber neck 6mm BR target rifle, which provides 0.002" neck clearance on the loaded round.
 
Also, shooters constantly talk of adjusting neck tension on a bullet.  I've got news for you... with correctly sized cases, it's pure b.s.!!!  I know this is controversial, but it's true.  No matter what your brass thickness is at the neck or no matter what size you make your necks during resizing, you will ALWAYS have approx. 0.001" press fit tension and no more.  The reason is simple -- when you seat your bullet, the bullet acts like a sizing button and resizes the neck some as it is being pressed into the case.  The bullet is thicker and harder than the thin case mouth and therefore resists deformation.  The thin case neck is compliant, readily deforming to the bullet when seated.  Not only have I proven this to my complete satisfaction time and time again by measuring the outside of the neck with micrometers before and after bullet seating, but the myth of variable neck tension is debunked in the opening chapter of the Lee "Modern Reloading, 2nd Edition" manual.  If your case neck is too thin, you can have too LITTLE neck tension, but you can't adjust neck tension greater than the 0.001" interference fit.


Edited by RifleDude - September/22/2008 at 17:34
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/23/2008 at 04:21
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Rifledude, Thanks for that explanation. I have been loading for a 30-06 for years which ate anything (allmost) I churned out on my Lee reloading kit. It seems as though I have not learnt much more then the basics !!!
So I appreciate all the comments and I am applying your advice and will sift through it all and eventually get to something that works.
 
I have shot 5 shot groups using fire formed Lapua and neck sized (13 th) cases, virgin Lapua cases and fire formed, neck sized PMP cases. (PMP is our local factory and reknown for average quality).
What is clear is that the Lapua cases worked equally well with grouping just a tad under 3/4inch. The PMP shot all over the place. It is thicker brass and probably needs a lower charge/pressure.
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/23/2008 at 09:43
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lee likes to debunk alot of stuff,  bullet crimping dies, different types of lub sizing dies. not sure they are correct on neck tension though. somewhat confused rifledude-- have run into cases, OFV military etc. where the neck tension was so tight it would crush the bullet. also and particularly for semi autos, I use a scale to push the loaded round against, rarely are the readings the same between lots of brass. perhaps we are looking from different reference frames.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/23/2008 at 17:57
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Unless you are using some seriously thick brass or very soft bullets, the thin walled case mouth simply doesn't have the yield strength to deform a jacketed or solid copper bullet of much greater wall thickness.  I'm not just going by what was said in the Lee manual, but again, I have proven this time and again with micrometers in my own reloading.  You can size the neck as small as you want and when you seat the bullet, the result is you will always get the same o.d. dimension on your mics when compared with any other sized case of the same neck thickness because seating the bullet expands the neck.  The reason there are different neck sizing bushings available is to accommodate different dimensions in competition chambers in conjunction with different neck turn thicknesses.  Even if you were in fact deforming the bullet with increased neck tension, you would get terrible accuracy as a result, because the bullet would no longer form a tight bore seal.

Edited by RifleDude - September/23/2008 at 18:00
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/23/2008 at 21:35
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Hey RifleDude
 
My question is:  Does the fact that the outside diameter of a loaded round is always the same mean that there is not a difference in gripping strength?
 
You put a clamp around a metal collet around a metal rod and start tightening, the grip strength will be greater the more you tighten the clamp.  The outside diameter of the clamp will always be the same but there will be more grip between the collet and the rod.
 
If you put a rubber band around a set of plans there will be a different grip depending upon how many wraps you put around it.
 
Maybe not good anologies but I don't know that it would follow that just because the outside diameter was the same that the bullet grip would be the same.
 
Just thinking.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/24/2008 at 19:48
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Originally posted by sakomato sakomato wrote:

Hey RifleDude
 
My question is:  Does the fact that the outside diameter of a loaded round is always the same mean that there is not a difference in gripping strength?
 
You put a clamp around a metal collet around a metal rod and start tightening, the grip strength will be greater the more you tighten the clamp.  The outside diameter of the clamp will always be the same but there will be more grip between the collet and the rod.
 
If you put a rubber band around a set of plans there will be a different grip depending upon how many wraps you put around it.
 
Maybe not good anologies but I don't know that it would follow that just because the outside diameter was the same that the bullet grip would be the same.
 
Just thinking.
 
Those are good analogies, but keep in mind the brass is thin and doesn't have a high yield strength.  Brass is so soft and malleable that it doesn't have much "memory" and once deformed, it doesn't spring back to its original shape very much.  Consider a case mouth has no more than perhaps 0.020" thickness.  During seating, it will immediately yield to the much thicker, harder bullet and it doesn't have enough mass to exert a great deal of gripping force on the bullet.  With the clamp analogy, you are exerting an increasing force on the rod from the energy you are putting into loading up the threads of the clamp and the collet is made of higher tensile strength material.  The rubber band has a great deal of elasticity and the more it grips, the thinner it gets at the same time.  When you measure the neck of several loaded rounds and it mics the same diameter and the difference between the bullet diameter and neck diameter is exactly the same as 2 X the wall thickness of the case before seating, regardless of the neck size before seating, logic tells me that up to a certain point, continually reducing neck diameter isn't gripping the bullet any harder.  Maybe with other materials, but not with soft brass.


Edited by RifleDude - September/24/2008 at 19:52
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/24/2008 at 20:45
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Correct me if I'm wrong. I thought that the process of neck turning was to size the case and or neck and expand the neck then turn the necks so that all the necks have the same wall thickness. This way when the bullit is seated the case neck would have the same tension on the bullit and lead to more consistent pressures on firing.
Most of the time isn't it that only the neck is sized and the shoulder set back so the case will fit the chamber that it was fired in, letting the case body center the bullit in the throat since the case body will have almost the same outer deminsions as the chamber's inner deminsions.
I also understand that most shooters like to have the inner deminsions of the neck .002 smaller than the  outter deminsions of the bullit.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/24/2008 at 20:53
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Originally posted by BeltFed BeltFed wrote:

Correct me if I'm wrong. I thought that the process of neck turning was to size the case and or neck and expand the neck then turn the necks so that all the necks have the same wall thickness. This way when the bullit is seated the case neck would have the same tension on the bullit and lead to more consistent pressures on firing.
Most of the time isn't it that only the neck is sized and the shoulder set back so the case will fit the chamber that it was fired in, letting the case body center the bullit in the throat since the case body will have almost the same outer deminsions as the chamber's inner deminsions.
I also understand that most shooters like to have the inner deminsions of the neck .002 smaller than the  outter deminsions of the bullit.
 
The reasons for neck turning are really twofold:
- to physically allow the round to chamber in a tight neck chamber
- to uniform the neck thickness so you have as little bullet runout as possible and therefore present the bullet to the start of the lands as concentric with the bullet centerline as possible.
 
Yes, it also helps control neck tension some, but my only point on that is after you reach approx 0.001" interference fit, continuing to size the neck smaller doesn't increase the gripping force, the brass simply yields.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/24/2008 at 21:52
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I have pulled a few bullets with an RCBS collet type puller.  There is definately a difference in the amount of force necessary to raise the handle and lower the ram to pull the bullet with differing inside neck diameters prior to seating a bullet.  I would be at a loss to explain that if there was not a different amount of grip on the bullet.
 
Another analogy:  If you have a 5/8" ID hose and a 1/2" ID hose that both have approx the same material thickness and you have a hose mending end to install, when you install the plastic male end of the hose mender into the hoses there will be a different force necessary.  When you pull the hose mender out it will take a larger force to pull it out of the 1/2" hose.  The more you stretch any material the more surface tension is created.
 
It does not make sense to me that there would not be more bullet grip on a case neck with a smaller inside diameter to start with.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/25/2008 at 14:59
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Originally posted by sakomato sakomato wrote:

The more you stretch any material the more surface tension is created.
 
 
That's true... UNTIL the yield strength of the material is overcome, beyond which point it either fails (harder more brittle materials) or conforms to the new shape (soft, malleable materials like brass) and further stretching beyond this point no longer results in greater tensile stress. With the hose mend analogy, you are still dealing with a very elastic material that tries to return to its original shape when deformed, so it can stretch a great deal and continue to exert greater strain on the object deforming it.  Yes, the brass is doing the exact same thing as the hose, and neck tension does indeed increase up to a certain point as the neck is reduced, except brass has very low modulus of elasticity, so once its yield strength is exceeded, it deforms to the new shape.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/26/2008 at 21:01
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A short answer; When you load it until the neck splits (fails) it's usefulness has been exceeded! We have a few guy's that pinch every penny and load until it fails. I don't throw money away but for the consistancy I want, five loads is all I'm confortable with. I have also just realized Bucky That I misinterperted this thread. I was thinking trimming for case length and did not catch on that it is about turning for neck thickness (even though it was stated clearly). I find myself doin that more often lately. Time to call for more thearpy!!
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