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Concentricity & Runout Correction

 
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  #1  
Old 05-27-2012, 11:32 PM
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Concentricity & Runout Correction

Ok, Long time Competitive Smallbore shooter, but I'm fairly new to Mid Range, Long Range, and Palma Competition as far as the reloading aspect of the game goes and only been reloading now for about a year for my .308 and those tournaments. I'm trying to pull out all the stops on precision and turning out consistant rounds. I do everything by hand , no case prep centers with power tools or anything. I know it takes longer but I enjoy the process. This season I've taken my process now into considering concentricity. I'm using the Sinclair Conc. Gauge, and I realized that some of the others had an advertised correction feature, but still went with the Sinclair. What I'm wondering is if anyone out there not using one with the feature to tip the bullet slightly, how do you attempt the slight correction, or do you attempt it at all, and if it's too far out of your acceptable range does that round just become a fouler or sighter ? I've been able to with a little slight pressure between my thumb and forefinger make a slight adjustment to the bullet if needed, and I can on average get my runout down to .001 or there abouts. My other concern is how much does anyone feel this alters neck tension adversely ?

C.D.
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Old 05-28-2012, 05:40 AM
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Re: Concentricity & Runout Correction

I think it's a bad idea to try to press the bullet back onto a perfect zero runout number. This would have the tendency to loosen the bullet in the case neck, reducing neck tension.

The runout correction tools assume a lot... assume being the operative word. They assume that the runout is caused by the bullet just needing a slight shift inside the case neck. They assume you can do this with with a little push to high side of the bullet...

...but in reality, you're probably just bending the case neck to make things look good. Or the case shoulder area. You could even be deforming the bullet, to some extent.

Runout under .005" never really seems to make a lot of difference.

Runout over that number needs to be corrected by preventing it from happening in the first place, with proper die set up and good brass, well prepped...

My opinion... but there it is.

Dan
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Old 05-28-2012, 06:56 AM
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Re: Concentricity & Runout Correction

I don't do corrections either. I also have the Sinclair.

That bullet enters the neck about straight in. Once you go "correcting" that seating, you risk the concentric neck integrity. Just a theory. I put my cases that would need correction in a separate batch and use them for foulers or fun plinking.

Boots once told me a story about how he accidentally shot his "bad batch" at a match and did the best group with them.
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Old 05-28-2012, 07:22 AM
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Re: Concentricity & Runout Correction

Over a few decades of high power competition, I've done several tests for accuracy with ammo with bullets somewhat crooked to the case axis. Very interesting results.

First off, the tool used and how it's set up make a big difference in what a given round shows its runout to be. As the .308 case centers its front end in the chamber by its shoulder mating perfectly with the chamber shoulder as the firing pin drives it there, that's where the front of the case is when it fires. If the case neck's well centered on the case shoulder and the case neck axis is in line with the body axis, the bullet held in that case neck's well aligned with the bore. It doesn't seem to matter if the case neck wall thickness varies 1/1000th inch; accuracy is just as good with such rounds as those with zero tolerance in neck wall thickness.

Second, it makes sense to me that the runout measuring tool should support the loaded round such that the case shoulder spins in something that keeps it concentric and the pressure ring on the case rests against something as that's the part of the case that gets pressed against the chamber by the extractor when it's loaded. In other words, the runout tool should hold the case the same way the chamber does. So I built my own with a nylon washer up front with a 3/8ths inch hole in it to hold the front of the case on its shoulder and the back end at the pressure ring rides in a V block of some sort. The dial indicator's plunger touches the bullet ogive about 1/10th inch back from its nose. No other runout gage I know of holds a case that way; they support the round different ways that don't indicate how the bullet axis will align with the chamber/bore axis. Most of them have the front support on the case body just behind the shoulder and any out of round dimension there adds to the bullet runout number; cases are not perfectly round at that point nor are chambers for that matter.

Third, .308's shoot very accurate with up to about 3/1000ths runout. When a few of us worked up a load for Sierra Bullets' first Palma 155-gr. bullet, several thousand rounds of ammo using it were made on two Dillon 1050 progressive loaders. Bullet runout measured up to 3 thousandths. A random sampling of 20 rounds were test fired from a Palma rifle (with a virtual SAAMI spec chamber) at 600 yards; they all went into 2.7 inches. Not bad at all for brand new unprepped cases (other than a Lyman expander to uniform the case mouth inside diameter) and a 3/10ths grain powder charge weight spread.

Using issued Lake City 7.62 NATO M118 and M852 match ammo, I've often seen their bullet runout as much as 8/1000ths. It's easily corrected by putting a .338 caliber collet in a bullet puller, then after doing runout tests on rounds marking the high spot on the case, put that round in the bullet puller holding the round by the case neck then pressing on the back end of the case to bend the case neck a bit. I've been able to do this getting bullet runout under 2/1000ths and the ammo shot very accurate; noticably more accurate than before.
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Old 05-28-2012, 11:13 AM
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Re: Concentricity & Runout Correction

I too have used a collet bullet puller like Bart B said but here is the same thing in a much simpler tool

TT-Equipment-Index

I also have a Bersin that works OK but there is always the concern that it is loosening the bullet grip
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  #6  
Old 05-28-2012, 11:25 AM
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Re: Concentricity & Runout Correction

Great info. How does the TT tool work if you turn your necks? Don't you take the risk of denting your necks if they don't fit perfectly in the hole?
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Old 05-28-2012, 11:56 AM
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Re: Concentricity & Runout Correction

Woods, Thanks for the link.

I drilled holes in side of my bench to do this but the wood elongates over time.

I just got done ordering the tool from the link.

Not sure this is how bench rest shooters would correct for minor amounts but even after going through many corrective measures and processes with my reloading efforts, I still have a few that need tweaked.
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