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Old February 14, 2010, 05:20 PM   #1
roc1
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Hornady Concentricity Gage

First of all I do not have any benchrest rifles. I would like to know if this Hornady Concentricity gage would help enough on standard loads for my rifles to make a difference in moa to justify buying it? I like to get the best out of my rifles but with a standard hunting rifle is this really going to help or not worth the effort? I know I can play with loads and get good groups.I have thought about this and also neck trimmers but did not know the best way to go or even if I should mess with it unless I get or build a truly target style rifle?
Thanks for help
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Old February 14, 2010, 08:02 PM   #2
rottieman33
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I just bought one for my Remington 700 .308 loads and I noticed a big difference in my grouping. Most of my rounds were .002-.003 out but did come across a couple that went from .004-.007. Its a nice tool easy to use.
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Old February 14, 2010, 08:50 PM   #3
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Thanks Rottieman33. Does it move the bullet back inline like it shows to do? Do you neck turn also or just use the Case gage? I am shooting a Remington 700 308 with a standard barrel not varmint . i would also use it on my other rifles 22-250 243 and 7-08.
Thanks for the help.
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Old February 14, 2010, 09:46 PM   #4
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I don't neck turn, not that picky about my loads but for the price of the Gage I couldn't pass it up. There is a couple of stuff on it i wish they would change. Wish the run out Gage was at a 45 deg angle and the nob to straighten bullet was bigger. I did send a email to Hornady to let them know.
The nice thing is you don't have to bolt it down to some thing.

Last edited by rottieman33; March 3, 2011 at 04:53 PM.
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Old February 26, 2010, 06:12 PM   #5
CAPT KURT
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Bullet run out

Most reloaders have heard of run out but do not understand the value of correcting it. 3 areas run out can occur 1) the bullet itself. 2) the casing neck. 3) the seating of the bullet. It is very important to check for any run out on the casing neck after sizing. Any run out there will transfer to the bullet after seating. After seating check for run out near the tip about 1/8" back. If run out is present, correct to less then .001 for best grouping. You will see a difference. You can also adjust factory ammo as well. Then test this for yourself. Groups will tighten, flyers will become a thing of the passed. And by the way, don't let anyone tell you a bullet will straighten itself out as it goes down the barrel. The bullet will carry the wobble down the barrel cutting uneven riflings in the bullet. As the bullet leaves the barrel, it will be spinning out of round and head off in the direction of wobble. This is why a good group can can ruined by a flyer with excessive runout from the rest of the group. Also neck turning can help in some cases, but there are some draw backs and one needs to know this before making that decision.

Last edited by CAPT KURT; February 26, 2010 at 06:21 PM. Reason: ADDING A FINAL STATEMENT
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Old February 26, 2010, 06:29 PM   #6
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Bullet run out

Most reloaders have heard of run out but do not understand the value of correcting it. 3 areas run out can occur 1) the bullet itself. 2) the casing neck. 3) the seating of the bullet. It is very important to check for any run out on the casing neck after sizing. Any run out there will transfer to the bullet after seating. After seating check for run out near the tip about 1/8" back. If run out is present, correct to less then .001 for best grouping. You will see a difference. You can also adjust factory ammo as well. Then test this for yourself. Groups will tighten, flyers will become a thing of the passed. And by the way, don't let anyone tell you a bullet will straighten itself out as it goes down the barrel. The bullet will carry the wobble down the barrel cutting uneven riflings in the bullet. As the bullet leaves the barrel, it will be spinning out of round and head off in the direction of wobble. This is why a good group can can ruined by a flyer with excessive runout from the rest of the group.
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Old February 27, 2010, 08:41 AM   #7
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Does the Hornady tool let you check runout of the case prior to reloading or just the loaded round?
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Old February 27, 2010, 08:43 AM   #8
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rottieman - Are those shafts shown in the second picture used for different diameter bullets? Do they all come with the tool or do you buy them separately?

Thanks for the pictures, they help the dialog a lot.
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Old February 27, 2010, 09:18 AM   #9
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I bought the gage from Hornady. The info with it says best results come from runout being kept to .002 to .003 tops. I saw several factory rounds I checked with a lot more than that.My loads pretty welled stayed in that range or it less the ones I have checked so far. I did correct a 1/2 box of the factory ones and am going to shoot some this afternoon and see if there is a difference. I guess if you corrected them down to .001 or .002 you might tell some difference there too. I will try it and see. I know with a factory rifle like all of mine are it might not make much difference but I will see.
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Old February 28, 2010, 04:25 PM   #10
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Methinks I need a new toy....I mean tool!. Been thinking about one for a few years and you guys talked me into it. Thanks!
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Old February 28, 2010, 06:40 PM   #11
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Case length must be trimmed for safety reasons, regardless of whether you are loading match ammo or not. Excess neck length can jam into the throat of rifling, preventing normal release of the bullet, thereby creating dangerous pressure. Don't load cases that exceed the SAAMI maximum length.

There was a good article in the American Rifleman in the 60's, reprinted in the NRA book, Handloading, in 1981, p. 87, in which the author, A. A. Abbatiello, ran tests using .30-06 with the 173 grain boattail NM FMJ bullet. It was measured for bullet tilt and segregated by how much tilt there was for the tests. The article is geared toward sorting cartridges by their runout rather than trying to correct it. Several interesting results were observed:

With rifles of the accuracy possible at the time with that bullet under ideal conditions it was found bullet tilt of 0.001" (this is tilt, not runout, and is equal to half the total indicated runout (TIR) on the gauge) would open the groups up 1/4 moa. The groups grew about 1/4 moa with every additional thousandth of tilt (or 0.002" of runout), and shot 1 moa bigger with 0.004" tilt (0.008" runout). Beyond 0.004" runout there was no further effect. The author speculates that tilt greater than 0.004" apparently straightens itself down to the level of the 0.004" tilt bullets, but no further.

The author marked the high side of the runout on the cartridge case, and if he oriented the mark the same way each time it cut the moa increase caused by the tilt in half.

Many years later, Harold Vaughn repeated the experiment with different, more precise equipment. A 6 BR rifle with integral linear ball bearing sliding machine rest. He got much smaller result. He tilted his bullets 0.215 degrees (measured average, I expect) which corresponds to 4 thousandths tile in the bigger .30 caliber bullet. He marked the high spots and fired 12 rounds, rotating the high spot 90 degrees each time. The resultant group was looked like a 4-leaf clover, with each leaf having 4 rounds through it, but they were all touching. The centers of the four leaves were about 0.2" across.

So, why the big difference in results? Several factors likely contributed. Vaughn found that if he seated the bullets to touch the lands, the dispersion decreased about 25%, the touch apparently tending to straighten the bullets some. He had to seat the rounds 0.030" off the lands to give them some runup to get the full effect.

But was it full? A. A. Abbatiello's ammo was SAAMI standard length, and probably a good bit further back off the lands. Might that contribute? Could a bullet with more speed arriving at the throat keep its tilt better while being swaged into the rifling?

Another factor could be bore precision. Today's custom barrels are undoubtedly better than yesteryear's. A benchrest gun in particular will be tighter in the chamber as well as the throat and should help keep overall cartridge alignment better. A. A. Abbatiello's guns could have had looser bores, freebores, and chambers, all?

The bearing surfaces of the bullets may be different in calibers, giving teh 6 mm better aligning ability than the grip the .30 cal bore could get on the 173's. The 6 mm bullets were flat base where the 173's were boattails, so the bearing surface difference seems likely.

And about those boattails: most of us have noticed that it is easier to get a flat base bullet shooting cloverleafs at short range than it is a boattail. Part of that is due to the dwell of the boattail in the muzzle blast as it gets clear of the muzzle tending to exaggerate error. It seems to me possible that the tapered side of a boattail slightly tipped into the blast stream could have rather more effect than the same tilt off a flat base equally tilted. This is just based on the surface angles presented to the blast.

It is also possible the different bullet styles have their centers of gravity so located as to exaggerate or minimize the effect?

So, as always YMMV. You should probably try Vaughn's experiment of picking out a dozen maximum runout rounds and marking the high spots and shooting them rotated at 90 degree intervals, then firing a dozen perfect rounds to compare. You want to find out what the process does for you? Considering Vaughn's results were 1/5 that of A.A. Abattielo's, there is obviously a range of importance of this factor to different gun, load, and bullet combinations.
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