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Headspace and case length for a newbie...

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 07:32
richardca99 View Drop Down
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As a new reloader about to get started, I'm trying to clear up some confusion.  You guys have been great about answering my questions, and I really appreciate it.  Here's a couple more...
 
I'm having a little trouble getting my head around the concept of headspace and case length.  I understand what they are, but I'm not 100% sure how I address them in the reloading process.
 
Headspace:  With once-fired brass that is neck-sized only, I'm assuming that headspace will be correct, as the case has been fire-formed to my chamber; if so, then headspace of a cartridge case is important when you full-length resize.  Am I correct?  With new brass, I assume that I don't have to worry about headspace, as you don't full-length size a new case.  If I'm missing the point entirely, please explain how I address headspace with my bolt guns to ensure that I'm optimizing accuracy.
 
Case length:  Am I to measure the chamber length of my guns's chamber and then just trim the case length to less than this measurement?  If so, how much less?  Or, are fired cases to be trimmed to a SAAMI spec?  How are case length and headspace typically addressed by the reloader.
 
FYI...I'm not a 6mm BR shooter, just a guy trying to work up really accurate deer loads for his sporter bolt guns. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 08:05
pyro6999 View Drop Down
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i full length new brass cause usually the mouths are messed up enough you can seat a bullet in them, of course this could be done with a neck sizer but since i dont have one i have to run the press about 3/4 of the way up to basically accomplish the same thing.
are talking about belted cases like a 7mm mag or standard cases i.e.  30-06 in reguards to headspace, cause they head space differently, most of  your standards space off the should where your magnums with belts space off the belt.
trimming: if you have the tools to measure chamber length i would use it, i myself trim a bit extra off my cases for expansion just in case insurance not much and extra turn or two maybe.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 08:28
Dale Clifford View Drop Down
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headspace is the concept that determines how you will load. no headspace is usually associated with, tight bolt closure, better accuracy, because the case is left to max. dimensions, in relation to the chamber, a lot of headspace means the case is min. dimension to the chamber, (or the same as a FL die) which increases feeding realiability but decreases the accuracy because the bullet is usually no centered in the bore.

If cases are too long the extra material is jammed into the start of the leade area and increases the pressure. cases get to long by repeated full length resizing which lengthens the brass on the down stroke when the shoulder is pushed back, (some sources say the expander ball pulls the neck longer--take your pick). thus a neck die gets around this process as does partial fl resizing.

usually after fire forming the case will be at a small rebound dimension smaller than the chamber-- just right-- this is the dimension you will want most of the time, and try to duplicate in the reloading process. many tools are available but the general principle is the same.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 08:43
Steelbenz View Drop Down
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Good question,
First I'd ask what reloading manual you are using, the Hornady handbook #7 has a great explanation of the case and chamber mechanics. The problem with Full length resizing is you lose that fire formed brass, the die squeezes the brass back to SAAMI diameter and your head spacing of the brass for your rifle is no longer good. Also, due to the chamber wall and the brass losing that hand in glove fit, it will also let the brass grow again causing weakening of the brass and pushing the neck forward again making trimming necessary. New brass will have the same problem until you fire it in your rifle. Once a case has been fired in your rifle head spacing really takes care of itself, unless the chamber of your rifle is jacked then you have more troubles than I can get into here. After cleaning fired cases always check them in good light and if your like me, old eyes, get a bench magnifying glass with lights built in. When looking at the head area of the case (extractor groove end) if you see cracks or spots that just don't look right scrap it.  Cases are cheap compared to eyes and facial burns and head failures even on bolt guns aren't funny. On to case length, I think your confusing case length and Cartridge Overall Length. (COL) Case length is just that the length of the case from head to neck, the actual area that the chamber holds, the other COL is what some people play with, its the distance between where the bullet sits in the chambered case and the land and grooves of the rifling in the barrel. There are special tools you can buy to check this. Also a few quick tricks,but as a new reloader I'd stay with adjusting powder charges and bullet weights before diving into the black arts. LOL If you haven't already bought a reloading manual I'd recommend the Hornady seventh edition just for what I wrote about earlier.  I work for Mercedes Benz not Hornady so I'm not trying to make a sale. LOL                  


Well, Dale and Pyro beat me to the punch,  LOL


Edited by Steelbenz - February/13/2008 at 08:49
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 08:46
pyro6999 View Drop Down
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i love my 7th ed hornady manual, but the 2nd ed lee has more reload data. i can see i need to buy a bunch of neck sizers
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 08:54
Steelbenz View Drop Down
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Dale,
  you reload just about everything don't you? If I remember right! Do you get the same from his question as I do? Case length VS Cartridge Overall Length.    
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 08:58
pyro6999 View Drop Down
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i thought he was just talking about case length myself
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 09:16
richardca99 View Drop Down
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I was talking about case length.  How do I know what dimension the case should be trimmed to, as I assume they all should be the same?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 09:18
pyro6999 View Drop Down
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the book should say max length, trim length, and max col
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 09:21
richardca99 View Drop Down
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So I should go with what the book says, not what I know my exact chamber length to be?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 09:25
pyro6999 View Drop Down
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not necessarily, do you have the dimensions handy?? what caliber are we talking about? i got my book right here with me
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 09:26
richardca99 View Drop Down
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.25-06, and the rifle is a Sako 85.  I'm willing to buy a gauge, but I don't know what I'd do with that value even if I measured it!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 09:32
tahqua View Drop Down
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I use Wilson case length gages across the board. It is simple because they are go-no go. If the case is outside the gage either body or neck, you're to long. Keep it above the minimum on the gage and your good to go. At least for hunting ammo.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 09:32
pyro6999 View Drop Down
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ok if you have a set of dial calipers measure the oal of the cases you have just grab any one of them and measure it.
max coal with bullet - 3.250
max case length- 2.494
case trim length- 2.484
 
see how they only take out .010 that should be perfect in about any rifle
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 10:50
Dale Clifford View Drop Down
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as tahqua suggests, wilsons are the best way to go as they catch small irregularties in the web area not visible. while hunting ammo is critical, match ammo is worse, and wilsons  are usually min. dimension.-- so each loaded round is test for go or no go- before the match. even then its no certainty.

usually too short of a case is not a problem , but too long is always a problem

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/13/2008 at 14:52
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http://www.opticstalk.com/forum_posts.asp?TID=8888
there is a lot of info here, but I found it interesting and informative. 
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