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Rifles, Reloading, Optics, Equipment
Gunsmithing
Dialing in bore for threading and chamber?
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<blockquote data-quote="Hired Gun" data-source="post: 1382485" data-attributes="member: 1290"><p>I use spiders on both ends with 3/8-24 threads with brass tips pointed up to a 1/8th inch contact points. I dial to zero run out at the throat and 2" ahead of that. I use a long rod held lightly in an o-ring in a drill chuck on the tailstock by the tail and on the barrel end a fitted bushing and a small weight to take up any clearance and a Starrett .0001" indicator riding on top of the rod as close as possible to the barrel. We only dial in the end we are working on in an effort to get the bullet into the bore as straight as possible. This method is commonly referred to as the Gordy Gritters method.</p><p></p><p>Any other method will show up in the bore scope as the rifling starting almost to the neck and the other side going out twice as far as it should before the rifling starts. The worse the curve the more exaggerated this will appear. With the chamber cut this way it is impossible to get the bullet to engrave the rifling perfectly square or at the same time. I believe it is a very big deal to keep the throat and chamber as square to the actual bore as straight as possible. We dial in the muzzle the same way 1/8th inch behind the exit and 2" back into the barrel to get the crown as square to the bore exit as possible. Dialing both ends at the same time it is impossible to achieve this level of precision. Even though both ends appear centered in the blank throughout the length of the barrel the bore wanders all over the place. </p><p></p><p>The lathe is a high precision Taiwan custom that weighs 2200 pounds on a 6" thick 5/8" rebar on a 12" grid slab of 4500 psi cement. It is checked every couple months or during the season changes with a Starrett 16" machinist level. It cuts threads we are very proud of. No, fancy threads do not do anything for accuracy but they are nice to look at and they make me feel good if someone ever were to disassemble one of our rifles looking for flaws. </p><p></p><p>To combat distortion none of the spider screws are set very tight. The brass gets a very firm grip on the barrels. In 9 years doing this full time we have never had one slip. Just taking nice light cuts and a fairly heavy lathe seems to be the key. The tennon is threaded without a relief cut so the barrel is as thick as possible in the chamber area. We use indexable carbide threading tools. Without sanding or lapping we can hold a cotton ball against the threads and they pull no visible lint. This lathe is only used for gunsmithing so it doesn't get beat up with heavy projects. I have access to a 16" Clausing Colchester for heavy stuff. </p><p> <a href="https://imageshack.com/i/np9abxj" target="_blank"><img src="https://imagizer.imageshack.com/v2/640x480q90/853/9abx.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a> </p><p></p><p>When it's time to clock the barrel in the action the curve is set to exactly 12 o'clock on the muzzle end. The flush system provides filtered and magnetic screened Rigid Extreme Performance cutting fluid at 100 psi. It's not about speed but in quality to keep all shavings and swarf away from the cutting edges. The chamber is single pointed to between .005" and .010" final chamber diameter at the same taper as the actual finished chamber. Only JGS reamers are used because as far as I know they are the only company that uses staggered spacing on the flutes along with other features to keep them from chattering. This is how they look before polishing. We have tried other brands and so far nothing else compares. I have pictures showing the difference and they are not pretty. </p><p></p><p><a href="https://imageshack.com/i/mht7qzj" target="_blank"><img src="https://imagizer.imageshack.com/v2/640x480q90/809/t7qz.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a></p><p> </p><p>One last little tip. We don't use carbide reamers. They are commonly oversize for production use and allow more touch ups and resharpening. You have to either check for yourself or ask because it's not marked on them or noted anywhere and is not common knowledge.</p></blockquote><p></p>
[QUOTE="Hired Gun, post: 1382485, member: 1290"] I use spiders on both ends with 3/8-24 threads with brass tips pointed up to a 1/8th inch contact points. I dial to zero run out at the throat and 2" ahead of that. I use a long rod held lightly in an o-ring in a drill chuck on the tailstock by the tail and on the barrel end a fitted bushing and a small weight to take up any clearance and a Starrett .0001" indicator riding on top of the rod as close as possible to the barrel. We only dial in the end we are working on in an effort to get the bullet into the bore as straight as possible. This method is commonly referred to as the Gordy Gritters method. Any other method will show up in the bore scope as the rifling starting almost to the neck and the other side going out twice as far as it should before the rifling starts. The worse the curve the more exaggerated this will appear. With the chamber cut this way it is impossible to get the bullet to engrave the rifling perfectly square or at the same time. I believe it is a very big deal to keep the throat and chamber as square to the actual bore as straight as possible. We dial in the muzzle the same way 1/8th inch behind the exit and 2" back into the barrel to get the crown as square to the bore exit as possible. Dialing both ends at the same time it is impossible to achieve this level of precision. Even though both ends appear centered in the blank throughout the length of the barrel the bore wanders all over the place. The lathe is a high precision Taiwan custom that weighs 2200 pounds on a 6" thick 5/8" rebar on a 12" grid slab of 4500 psi cement. It is checked every couple months or during the season changes with a Starrett 16" machinist level. It cuts threads we are very proud of. No, fancy threads do not do anything for accuracy but they are nice to look at and they make me feel good if someone ever were to disassemble one of our rifles looking for flaws. To combat distortion none of the spider screws are set very tight. The brass gets a very firm grip on the barrels. In 9 years doing this full time we have never had one slip. Just taking nice light cuts and a fairly heavy lathe seems to be the key. The tennon is threaded without a relief cut so the barrel is as thick as possible in the chamber area. We use indexable carbide threading tools. Without sanding or lapping we can hold a cotton ball against the threads and they pull no visible lint. This lathe is only used for gunsmithing so it doesn't get beat up with heavy projects. I have access to a 16" Clausing Colchester for heavy stuff. [URL='https://imageshack.com/i/np9abxj'][IMG]https://imagizer.imageshack.com/v2/640x480q90/853/9abx.jpg[/IMG][/URL] When it's time to clock the barrel in the action the curve is set to exactly 12 o'clock on the muzzle end. The flush system provides filtered and magnetic screened Rigid Extreme Performance cutting fluid at 100 psi. It's not about speed but in quality to keep all shavings and swarf away from the cutting edges. The chamber is single pointed to between .005" and .010" final chamber diameter at the same taper as the actual finished chamber. Only JGS reamers are used because as far as I know they are the only company that uses staggered spacing on the flutes along with other features to keep them from chattering. This is how they look before polishing. We have tried other brands and so far nothing else compares. I have pictures showing the difference and they are not pretty. [URL=https://imageshack.com/i/mht7qzj][IMG]https://imagizer.imageshack.com/v2/640x480q90/809/t7qz.jpg[/IMG][/URL] One last little tip. We don't use carbide reamers. They are commonly oversize for production use and allow more touch ups and resharpening. You have to either check for yourself or ask because it's not marked on them or noted anywhere and is not common knowledge. [/QUOTE]
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Dialing in bore for threading and chamber?
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