Help with a sinclair concentricty gage

[Bart B.]

Below the bullet is rubbing the chambers throat and your Dixie cup within a Dixie cup isn't working.

The case and chamber shoulders are the Dixie cups. They work all the time when fired.

Don't know when the bullet got wiped. Need to know that for further analysis. I've seen that happen ejecting a round while the inline ejector was tilting the case and bullet against the freebore.

I think your Dixie cup hat in the Navy has effected your judgment.

It really did. Made it much better figuring out how simple cartridge positioning in chambers and runout gauges works. Watching case mouths center in chamber mouths was educational.

 

[mike a]

Thanks for all the replys, When I have the loaded round on both bearing blocks and the pin on the bullet I will get a movement or deflection of about two indicator marks but the same round will measure less movement with the brass only on the rear block and the bullet on the front block. I also have a problem when rolling the round trying to keep it smooth as it moves. Does anyone have a better process for moving the round with out a lot of jumping?

Hey wanttobe, to reduce jumping adjust the dial as high as possible. So there is very little spring pressure pushing down on the Bullet. Thus not pushing the rear of the case up. Very clean cases and a little lube on the balls.

 

[wanttobe]

Hey wanttobe, to reduce jumping adjust the dial as high as possible. So there is very little spring pressure pushing down on the Bullet. Thus not pushing the rear of the case up. Very clean cases and a little lube on the balls.

Thanks Mike, I sure do thanks each for their comments, All have taken this to another level. But I am even more at a lost now with all this information for knowing when the loaded round is truly concentric. I guess that this is more of an issue than I thought, may have to start at the beginning an re think my process.
Also a bit of infor for all, I load for a 223 an 6.5 CM, both are bolt guns and only neck size with a lee collet neck die and seat both with a forster ultra seater die.

 

[barefooter56]

Thanks Mike, I sure do thanks each for their comments, All have taken this to another level. But I am even more at a lost now with all this information for knowing when the loaded round is truly concentric. I guess that this is more of an issue than I thought, may have to start at the beginning an re think my process.
Also a bit of infor for all, I load for a 223 an 6.5 CM, both are bolt guns and only neck size with a lee collet neck die and seat both with a forster ultra seater die.

wanttobe,
When you use the Sinclair Concentricity Gauge you should have the probe of the dial indicator as close to the bullet/ case mouth junction as you can without the probe being able to contact the cartridge case mouth as you spin the cartridge. Also you always want to pre-load the dial indicator 10 or 15 thousandths on the item you are measuring . Then re-zero the dial indicator before doing any measuring so the probe always remains in contact with the item being measured. Most complaints we got on "excessive runout" of a cartridge case or a cartridge case with the bullet seated we got at Sinclair were from customers measuring new cartridge cases. Keep in mind that a new cartridge case is just a hammered piece of brass made to fit in all chambers made for that cartridge ( excepting custom or "tight-neck" versions). So think of your rifles chamber as the last formation die the cartridge case goes through. As the cartridge case is blown out during firing it acts like a toothpaste tube squeezed at one end and straightens out. That may be some shooters talk about the accuracy gotten shooting new brass. Check your once fired brass as it comes out of the chamber about in the middle of the neck. Then again after the cartridge case has passed through your neck or full length die. Then lastly after seating a bullet as described above. This will help you find IF there is an issue with your chamber or a die . And if it is a die , which one it is. Fred Sinclair told us he found that 0- to .005 runout did not seem to affect accuracy in his testing with his bench rest rifle.
Most of the time your dies can be corrected by checking the decapping assembly for being centered in the die, placing an o-ring under the lock ring so the die floats in the threads or even just backing the lock ring set screw away from the threads of the die. "Floating" a die in the threads of the press can help the die center up on the cartridge case as it goes up in the die. FORSTER presses work on this principle.

 

[Bart B.]

Floating" a die in the threads of the press can help the die center up on the cartridge case as it goes up in the die.

Do all shell holders have zero clearance to case rims so case heads cannot slide around a few thousandths allowing the case body to center in the chamber of a sizing die fixed in place?

And zero clearance from press ram to frame so the shell holder's slot cannot center off the die axis? How much slop does your press ram have at the top of its stroke just below the die?

Perhaps all the dies at each stage of case forming should be floated the same way.

There must be case rim clearance in bolt heads' "shell holder" because floating the barrel in receiver threads probably won't work.

Next, we may want to float all the bullet making dies so they're more uniform.

 

[Bart B.]

A perfectly straight cartridge measuring:
• 2.000” from body pressure ring to case shoulder
• .333” from shoulder to case mouth
• .667” from case mouth to bullet tip
will have its bullet tip center axis off bore center this amount upon firing, with the case shoulder centered in the chamber shoulder, for these chamber positions:
• Pressure ring centered in chamber, 0” at case mouth, 0” at tip.
• Pressure ring .001” off center against chamber, .000167” at case mouth, .000500” at tip.
• Pressure ring .002” off center against chamber, .000333” at case mouth, .001000” at tip

Spinning the cartridge any amount won't change these readings.

If the case neck and bullet axis is any angle to the case axis, these numbers change.

It's the teeter totter syndrome; one end moves opposite the other, shoulder is the fulcrum.