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Rifles, Reloading, Optics, Equipment
Reloading
Chambered Round Alignment to Bore; Neck Sized vs Full Length Sized
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<blockquote data-quote="Trickymissfit" data-source="post: 647212" data-attributes="member: 25383"><p>I can understand your thoughts on a die not matching the chamber, and your preaching to the chior. If you ream a chamber with one of the better brand reamers you automaticly double any error ground in the reamer. There is no way out of it. I've never been inside one of the big reamer shops, so I don't know what they are using to grind with, but have a rough idea. I suspect they are are using something like a Starr or a Walther CNC cutter grinder. They will grind a typical reamer to about +/- .000125, or a .00025" window. They will grind closer, but you have to have two grinders that are identical with different wheels plus a lap. The real problem is not grinding the body, but grinding the shoulders and neck concentric with the long taper in the body. But you can get it very close with a lot of crossed fingers and no coffee. So you gt a reamer that has about .00015" error ground in the body and another .0002" in the shoulder concentricity (actually the neck isn't that hard). When you use it those numbers will double even if the barrel is not turning. If you have the barrel rotating at the sametime you automaticly add in the error from the spindle group (bearings, and machine alignments). I had hundreds of reamers ground every year that were very similar to a chamber reamer in steps and sizes, and you soon learn what the nature of the beast is. Plus those two grinders are considered to be the cadillacs of cutter grinders.</p><p> </p><p>Then we get into making dies. Most all are lathe turned, and maybe have a finish reamer run thru them to take the last .005" out of them (or less). I rteally don't know the exact material they are using, but I also know what it's not. I suspect it's 4xxx steel that nitride hardened by the way it cuts. You ream that bore and leave about .0005" in it and have it hardened, and then polish the bore. (I know of at least one die manufacturer that does not polish the bores by the way). That piece of steel will change slightly, and usually less than .001". So you got a really pretty new die set and a finish reamed barrel off somekind of a national match reamer. Guess what? They will not match up exactly. I don't care who made the die or ground the reamer; they never will be near perfect.</p><p> </p><p>As I've said in the past the most accurate reamer on this planet is a Mapol reamer, and they don't come cheap. If a rifle manufacturer decided to use a Maypol reamer to cut his .308 N.M. chambers they would all run with in .0002", but also add about $150 to each rifle. Still every chamber cut would be nearly identical. In theory you could also ream the die with this reamer setup, but who could afford them? I've made forming dies on an Okuma before out of A2. Turned them to size and heat treated them. Still had to polish about .0005" out of them (a real PIA), and I didn't hold the necks all that close (+/-.003", and never could get a really close shoulder concentricity to the body taper (maybe .0015"TIR). And that was by single pointing it with several extremely light passes to take up the tool pressure load. But they were good enough for forming cases, but not good enough for resizing cases in my book.</p><p>gary</p></blockquote><p></p>
[QUOTE="Trickymissfit, post: 647212, member: 25383"] I can understand your thoughts on a die not matching the chamber, and your preaching to the chior. If you ream a chamber with one of the better brand reamers you automaticly double any error ground in the reamer. There is no way out of it. I've never been inside one of the big reamer shops, so I don't know what they are using to grind with, but have a rough idea. I suspect they are are using something like a Starr or a Walther CNC cutter grinder. They will grind a typical reamer to about +/- .000125, or a .00025" window. They will grind closer, but you have to have two grinders that are identical with different wheels plus a lap. The real problem is not grinding the body, but grinding the shoulders and neck concentric with the long taper in the body. But you can get it very close with a lot of crossed fingers and no coffee. So you gt a reamer that has about .00015" error ground in the body and another .0002" in the shoulder concentricity (actually the neck isn't that hard). When you use it those numbers will double even if the barrel is not turning. If you have the barrel rotating at the sametime you automaticly add in the error from the spindle group (bearings, and machine alignments). I had hundreds of reamers ground every year that were very similar to a chamber reamer in steps and sizes, and you soon learn what the nature of the beast is. Plus those two grinders are considered to be the cadillacs of cutter grinders. Then we get into making dies. Most all are lathe turned, and maybe have a finish reamer run thru them to take the last .005" out of them (or less). I rteally don't know the exact material they are using, but I also know what it's not. I suspect it's 4xxx steel that nitride hardened by the way it cuts. You ream that bore and leave about .0005" in it and have it hardened, and then polish the bore. (I know of at least one die manufacturer that does not polish the bores by the way). That piece of steel will change slightly, and usually less than .001". So you got a really pretty new die set and a finish reamed barrel off somekind of a national match reamer. Guess what? They will not match up exactly. I don't care who made the die or ground the reamer; they never will be near perfect. As I've said in the past the most accurate reamer on this planet is a Mapol reamer, and they don't come cheap. If a rifle manufacturer decided to use a Maypol reamer to cut his .308 N.M. chambers they would all run with in .0002", but also add about $150 to each rifle. Still every chamber cut would be nearly identical. In theory you could also ream the die with this reamer setup, but who could afford them? I've made forming dies on an Okuma before out of A2. Turned them to size and heat treated them. Still had to polish about .0005" out of them (a real PIA), and I didn't hold the necks all that close (+/-.003", and never could get a really close shoulder concentricity to the body taper (maybe .0015"TIR). And that was by single pointing it with several extremely light passes to take up the tool pressure load. But they were good enough for forming cases, but not good enough for resizing cases in my book. gary [/QUOTE]
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Chambered Round Alignment to Bore; Neck Sized vs Full Length Sized
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