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Concentricity - setting up dies - runout

 
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Old 05-03-2011, 09:19 AM
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Concentricity - setting up dies - runout

I just ordered a Hornady Concentricity Gauge. I keep reading about setting up dies correctly to minimize run out. So how do you set up dies differently? Granted I don't have results from measurements yet but want to understand how to tweak dies for minimum run out. Thanks
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Old 05-03-2011, 11:55 AM
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Re: Concentricity - setting up dies - runout

Hornady's Concentricity gage has a way to hopefully bend a round straight. Okay. But I don't care for bending anything to correct an error, rather use my gages to find where the non-concentricity comes in an fix it there.

Several things contribute to runout, I've never found "die set up", as such, to be a big issue.

Bad case necks, that is non-concentic necks, is the biggest factor. If the necks aren't straight no die can make them so. For factory (loose) chambers, lightly skim turning necks will improve the consistancy but making the mecks too thin adds it's own problems to the already loose fit.

It helps if the expander ball is bullet diameter or no more than a thou smaller. Most sizers squeeze case necks much too small and then we drag a short expander ball back out. That extraction pull tends to drift to the thin/soft side and pulls a formally straight neck to an offset angle; not good! Using an outside expander die/plug that pushes in rather than out, such as Lyman's "M" expander helps a lot.

Excessive 'bullet tension', any more than maybe 2 thou, frequently causes bullets to tilt during seating. No presumed tricks such as seating part way, turning the case and completing seating can do anything significant to reduce it either, the die's internal fit is usually too loose for that to really matter.

I LOVE Lee's collet neck sizers, they do not make the necks too small (So, some owners insist on grinding the inner mandrel down to make it so!). The collet fingers work to make the ID correct for best seating AND does it in such a way as to leave the sized necks about as straight as the brass itself will permit. The Lee collet has a moving part and that seems to buffalo some users but anyone willing to learn to use it correctly will be happy.

When I need to FL size my precision cases I use a body die and finish with the Lee Neck Die.

It is possible to use a "bushing" type neck die but all that can do is make the external neck diameter consistant. If the necks are not turned to a consistant thickness the difference will be forced inside and that will cause variation in bullet grip and that is NOT good for accuracy! Many bushing die users want a 'high bullet tension' (more than 2 thou,) and that increases the average runout from seating in a too tight neck.

With good necks, properly sized, a really good seater finishes the job. ONLY the Forster BR and Redding Competition dies have a "staight line" seater design. Their heavy inner spring loaded guide sleeve fully contains both the bullet and case in line before seating starts. (The various micrometer type seating heads are user helps only, they do nothing to make the ammo straighter.)

Last edited by boomtube; 05-03-2011 at 12:05 PM.
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Old 05-04-2011, 06:44 AM
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Re: Concentricity - setting up dies - runout

May 3rd, 2011
Try Using O-Rings with Sizing Dies for Reduced Neck Run-out
Hereís an inexpensive procedure that can help you load straighter ammo, with slightly better measured concentricity (i.e. less run-out) on the case necks and bullets. Simply use a rubber O-Ring on the underside of the die locking ring. This allows the die to self-align itself (slightly) to the case that is being sized. Without the O-Ring, if the flat surface on the top of your press is not perfectly square with the thread axis, your die can end up slightly off-angle. This happens when the bottom of the locking ring butts up tight against the top of the press. The O-Ring allows the die to float slightly, and that may, in turn, reduce the amount of run-out induced during case sizing.



Top prone shooter German Salazar has tried this trick and he says it works: ďGo to your local hardware store and get a #17 O-Ring (thatís the designation at Ace Hardware, donít know if its universal). Slip the O-Ring on the die and re-adjust the lock ring so that the O-Ring is slightly compressed when the die is at the correct height. Size and measure a few more cases. You will probably see a slight improvement in neck concentricity as the die can now float a bit as the case enters and leaves it. This isnít going to be a dramatic improvement, but itís a positive one.Ē We want to stress that adding O-Rings to sizing dies may help some reloaders, but we donít offer this as a panacea. Try it ó if using the O-Ring reduces measured runout thatís great. If it doesnít, youíve only spent a few pennies to experiment.



Lee Precision makes die lock rings with built-in O-Rings. Leeís distinctive lock ring design allows the same kind of self-alignment, which is good. However, Lee lock rings donít clamp in place on the die threads, so they can move when you insert or remove the dies ó and that can throw off your die setting slightly. By using an O-Ring under a conventional die lock ring (that can be locked in place), you get the advantages of the Lee design, without the risk of the lock ring moving.
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Old 05-04-2011, 07:28 AM
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Re: Concentricity - setting up dies - runout

Gene raises a good point about the effect of O rings under the die lock nuts. It's intuitive for most of us that it should be great if we use a wrench to lock dies down hard; it's NOT! A hand tight die is plenty tight and even that can be over done. I've taught my right hand to be consistant in installing each die to a snug but not hard fit; that alone allows for a bit of mechanical slack in the mounting even without rubber rings.
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Old 05-04-2011, 07:44 AM
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Re: Concentricity - setting up dies - runout

Quote:
Originally Posted by boomtube View Post

No presumed tricks such as seating part way, turning the case and completing seating can do anything significant to reduce it either, the die's internal fit is usually too loose for that to really matter.
I agree with everything Boomtube said, very good advice....... except this part. Everyone may not see improvements with this method, but I sure do. I will typically size using about 7 or 8 partial strokes, then do the same with seating the bullet, taking special care with initially starting the bullet in the neck. I will lightly "tap" the bullet, then rotate and "tap" again with ever increasing pressure until the bullet gets fully started in the neck. Then I go ahead and seat it with one or two more strokes.

While I do load for several calibers, most of my loading is done for a couple of custom rifles using custom dies made by the rifle maker. With the EXACT same set up I can size and seat using a single stroke each and my runout will about .003 to .004 on average. I can use the method described earlier and reduce the runout down to LESS than .001 on 80% and no more than .002 on the rest.

One of the most respected smiths on this site suggested I try this a few years back when I was struggling to reduce runout. (don't wan to drag him into this or I would mention his name)

The way it was explained to me is that every die has some error however slight, and the same goes for every press. When you rotate the case during sizing or seating, you are spreading that error out over several points rather than all the error being in one direction.

I am not a machinist, so I am not going to claim I really understand fully how or why this works. I do know it works for me. I am skeptical enough to keep trying to prove it wrong. In the middle of loading 20 rounds I often take 1 and just size and seat in a single stroke, runout will almost always be at least (often more) .002 more than the rest of my loads. I will also admit to being a little "obsessive" about runout. Many well respected shooters will say that around .003 or .004 is "good enough". My equipment is usually set up to produce that level of runout even without rotating.

I'm certainly not trying to start an argument with boomtube, and will admit to being wrong before (only once or twice if you don't ask my wife) but the "rotate" method sure seems to work for me.
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Old 05-04-2011, 09:17 AM
dig dig is offline
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Re: Concentricity - setting up dies - runout

All great advice, I will try the "O" ring on by Turret Press, I am thinking my Forster probably eliminates this problem anyway as the die sort of "floats" and self aligns. I am using almost all Redding Dies but have found the decapping rod/expander is never perfectly strait, will the "O" ring help with this as well, anyone tried it?

Again, think I am am ahead of the game as I have not started measuring yet but look forward to further improving with these techniques!

Thanks,
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Old 05-04-2011, 10:13 AM
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Re: Concentricity - setting up dies - runout

Hate to be discouraging, but I think you've started off wrong already..
For one, you can't measure 'runout' with the Hornady tool. So it won't help an endeavor to reduce runout.
You should have gone with a Sinclair concentricity gage(which is actually a runout gage) instead. It would have been the same cost: Sinclair Search : Reloading Equipment : Measuring Tools : Concentricity Gauges -
Or the NECO, but it cost a little more.

There are very important differences, which will be completely hidden from you using that Hornady...
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