runout from sizer die?

[pearson1662]

My 6.5mm Swedish RCBS dies show just less than .002" runout when measuring the expander decapping rod but .007" runout when measured at the expander ball. Could this be responsible for the large amount of runout that I'm getting? Can I just replace the expander ball? Will that fix the problem? Can I get a carbide expander ball for it? Thanks, Jay

[Wildalaska]

What kind of brass are you using?

WildcuriousAlaska

[pearson1662]

R-P

[Wildalaska]

Change cases before you change dies

In 6.5x55, Rem brass is said to be out of spec.

WildlapuaAlaska

[pearson1662]

Says who? Not sayin it isn't so, but Remington is a fairly reputable co. and I've not heard that before. Do you mind giving some references? Thanks for the feedback, Jay

[Wildalaska]

I think I saw that on the reloader bench bb, I also think that rem 6.5x55 doesnt have the same head dimensions as Norma/Lapua 6.5x55

WildiwilltrytofindreferenceforyouAlaska

[Unclenick]

Most of the less expensive commercial brass is less precise than, say, Norma, which is excellent. I have measured up to 9 mils (0.009") of web thickness variation in WW .308 brass using NECO's gage system, which let's you measure case wall thicknesses quite literally inside and out (www.neconos.com). My Norma 6.5-284 brass has never shown more than 1 mil of runnout on this gage; but then I paid almost 70 cents apiece for it.

Runout in the sizing die could render your casehead out of square, if it is angularly off axis, or, if it is a parallel axial offset, cause no case problem at all since the shell holder will usually let the case slip a little off axis as needed.

Having said that, it assumes the problem is with the brass. It probably isn't. You referred to runnout, but if what you measured is runout of a loaded cartridge at the neck/brass junction on a runout gage (bullet tilt runout), then the problem is almost certainly your seating die and not the brass or the sizing die.

I loaded 30-06 using both RCBS and Redding standard die sets for a couple of years in the 80's. Both assembled cartridges with bullet tilt runout of up to 8 mils. I then bought a Redding Competition Seater die. No cartridge runout ever measured greater than 2 mils after that, and those that did invariably proved to have case necks 2 mils thicker on one side than the other (this was mostly Lake City military brass back then). My dad acquired an RCBS side-loading precision seating die at the same time, but my Redding always beat it by almost 2:1 in precision. I've been buying and using the Redding competition seaters for all rifle calibers ever since.

Nick

[pearson1662]

I was just wondering if replacing the expander ball would help. Jay

[Unclenick]

Pearson,

Could you detail how you are measuring runout? Do you have conventional micrometer, runout gage (if so, whose), etc.? If you are thinking of changing the expander ball, I infer you think the case neck is out-of-round. If so, the brass probably isn't the same thickness all around and you need to think about some light neck turning.

Nick

[pearson1662]

Again, thanks for the feedback. I'm using the RCBS Case Master Gauge. I removed the decapping pin and runout at the case mouth went to .001" or less on most cases. A few were still .003 but I assume those are probably due to case wall thickness variations. However, case necks are too tight without the expander ball and I would have to get a universal decapping die to decap primers. If the case mouths weren't so tight I'd just polish down the expander ball. It has been suggested that I go to a bushing style die.

It seems like from some of the posts that there might be some confusion as to where I was measuring the runout that I reported in my first post. The reason I took the die apart in the first place was that I measured loaded cartridges at the bullet that had runout varying from .005" to .019". I removed the decapping pin and measured concentricity of the actual rod at the ball and without the ball. There is runout in the rod but significantly more measured with the ball on. Maybe no one is confused but me. Thanks guys.

[Unclenick]

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

[pearson1662]

I'll get to work with the unfired brass. BTW WildAlaska, I was pricing Lapua brass at Midway and looked at the reviews and Charles Hipsher of Logansport, IN says "American made brass is incorrectly sized resulting in gas blowby (dirty brass) Lapua and Norma brass is correct diameter." Not that I rely on Midway's customer reviews as my primary source for expert/accurate information but I thought you might find that interesting. Or not.
Jay

[Wildalaska]

I saw that review....check www.reloadbench.com for more info.....

Wild6.5Alaska

[pearson1662]

WildAlaska,
I found this in a post from "bfoster" who has a few credentials:

"You may want to check the head size, including the rim of your brass. S&B brass in 6,5 X 55, like most brass of European origin, is larger by some 0.006-0.008" than U.S. made brass. Some lots of Euro brass won't properly fit U.S. made shellholders that are near minimum size for the rim dimension." (Posted 01-12-2003 on Reload Bench Bulletin Board)

Thanks for the directing me to some good info. Jay

[pearson1662]

If anyone is still interested, I sanded the expander ball down till it didn't make any contact with the case neck (no expansion of case mouths after sizing) and rotated the bullets twice 90 degrees during bullet seating. The bullets will go in without case neck expansion. Total runout now is .002" or less for about 90% of loaded cartridges! The unacceptable 10% I attribute mainly to bad brass. Thanks, Jay

[Unclenick]

Did you try the rotation before reducing the expander? If so, what result did you get?

Nick