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**Unclenick** · May 23, 2005, 09:56 AM

Pearson,

Thanks for the clarification. 19 mils. Wow! That is a lot of runout. Let's see what isolating the variables tells us?.

First, do you have any new unfired brass? If so, or if you can acquire some and load it without first running through the sizing die, then you will be able to measure how much of your problem is due to the seating die and the unmodified brass?

Second, I looked at an RCBS sizing die I bought about six years ago. Assuming yours is the same design, the expander ball is a small diameter on the decapping pin retainer. I applied the micrometer to the ball segment on mine all around, and found it was round to within a couple of tenths of a mil (0.0002"). The threads on the end of the pin have about 2 mils of runout with respect to the rod body, and I expect the ones on the collet closing nut that fixes the depth of the decapper/expander rod on the top of the die does too; or more. Most threads formed by die cutting or rolling, and not cut or ground on a lathe, tend to have this kind of error.

The thread error can leave the decapper rod off-center, but this shouldn’t matter much. In the RCBS design, with the die adjusted to deprime cases, the expander ball is engaged far below where the die walls constrain the case. Thus the decapping/expander rod should flex enough and the case should be able to move in the shell holder enough to allow the expander ball to center itself in the case neck. At this point, as long as the ball is round, the fact it dangles a few mils off-center just shouldn't make much difference.

If applying the micrometer shows your expander ball is out of round, get RCBS to replace it. This is a heat treated part and can warp. If you have to replace it, I recommend you try to find an aftermarket carbide ball replacement so you don't have to fuss with inside neck lube any more.

The seating die is still usually the greatest source of trouble. Take out the ram in yours and put one of your bullets in it and see how well it prevents tipping? Usually it won't be great, since the die is designed to try to accommodate all bullet shapes. The worst case is a long bullet that tips easily. See the illustration at the bottom of this web page: http://www.forsterproducts.com/Pages/dies.htm.

You can try turning your cartridge as you seat. That is, seat the bullet just a tiny bit, lift the press arm and rotate the bullet about 1/3 turn and seat a little further, lift and turn another 1/3, then complete seating. I've also heard of people doing this in two steps with 1/2 turn.

I have spoken with people who set their seating die up to seat all their bullets only about .05". They then put them in the runout gage and push them into alignment by thumb, since the short seating depth doesn't hold the bullet very firmly. Once they have adjusted all their rounds to under 0.004" of runout, they set the seater down to final depth and run them all through it again. Once aligned, they don’t tend to tilt again. By the way, 0.004” of runout is the smallest number most people report seeing make a difference on the target. Bench rest shooters probably see much less. I always reject anything over 0.002" for conventional matches; just being finicky.

You can also try the rotation trick with your sizer ball. Pull the case down over the ball, rotate 1/3 and push it up over the ball again, rotate 1/3 and pull it back off again. Try 1/2 turn, too, if that doesn't do it.

All this rotating and pulling is a bloody nuisance, but at least you will find which loading stage is causing the real problem? After you do, you will want to get dies good enough to let you ignore the problem. In addition to that, getting good brass to start with is well worth it. You can do this by buying a premium brand like Norma or by sorting a quantity of less pricey stuff both by weight (after trimming uniform in length) and by gauging wall thickness variation.

Let me know how this turns out?

Good luck,
Nick

May 23, 2005, 09:56 AM	#11
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,060	Pearson, Thanks for the clarification. 19 mils. Wow! That is a lot of runout. Let's see what isolating the variables tells us?. First, do you have any new unfired brass? If so, or if you can acquire some and load it without first running through the sizing die, then you will be able to measure how much of your problem is due to the seating die and the unmodified brass? Second, I looked at an RCBS sizing die I bought about six years ago. Assuming yours is the same design, the expander ball is a small diameter on the decapping pin retainer. I applied the micrometer to the ball segment on mine all around, and found it was round to within a couple of tenths of a mil (0.0002"). The threads on the end of the pin have about 2 mils of runout with respect to the rod body, and I expect the ones on the collet closing nut that fixes the depth of the decapper/expander rod on the top of the die does too; or more. Most threads formed by die cutting or rolling, and not cut or ground on a lathe, tend to have this kind of error. The thread error can leave the decapper rod off-center, but this shouldn’t matter much. In the RCBS design, with the die adjusted to deprime cases, the expander ball is engaged far below where the die walls constrain the case. Thus the decapping/expander rod should flex enough and the case should be able to move in the shell holder enough to allow the expander ball to center itself in the case neck. At this point, as long as the ball is round, the fact it dangles a few mils off-center just shouldn't make much difference. If applying the micrometer shows your expander ball is out of round, get RCBS to replace it. This is a heat treated part and can warp. If you have to replace it, I recommend you try to find an aftermarket carbide ball replacement so you don't have to fuss with inside neck lube any more. The seating die is still usually the greatest source of trouble. Take out the ram in yours and put one of your bullets in it and see how well it prevents tipping? Usually it won't be great, since the die is designed to try to accommodate all bullet shapes. The worst case is a long bullet that tips easily. See the illustration at the bottom of this web page: http://www.forsterproducts.com/Pages/dies.htm. You can try turning your cartridge as you seat. That is, seat the bullet just a tiny bit, lift the press arm and rotate the bullet about 1/3 turn and seat a little further, lift and turn another 1/3, then complete seating. I've also heard of people doing this in two steps with 1/2 turn. I have spoken with people who set their seating die up to seat all their bullets only about .05". They then put them in the runout gage and push them into alignment by thumb, since the short seating depth doesn't hold the bullet very firmly. Once they have adjusted all their rounds to under 0.004" of runout, they set the seater down to final depth and run them all through it again. Once aligned, they don’t tend to tilt again. By the way, 0.004” of runout is the smallest number most people report seeing make a difference on the target. Bench rest shooters probably see much less. I always reject anything over 0.002" for conventional matches; just being finicky. You can also try the rotation trick with your sizer ball. Pull the case down over the ball, rotate 1/3 and push it up over the ball again, rotate 1/3 and pull it back off again. Try 1/2 turn, too, if that doesn't do it. All this rotating and pulling is a bloody nuisance, but at least you will find which loading stage is causing the real problem? After you do, you will want to get dies good enough to let you ignore the problem. In addition to that, getting good brass to start with is well worth it. You can do this by buying a premium brand like Norma or by sorting a quantity of less pricey stuff both by weight (after trimming uniform in length) and by gauging wall thickness variation. Let me know how this turns out? Good luck, Nick