Concentricity??

M

muslmutt

Guest
I recently obtained a Sinclair Concentricity gauge. Upon checking my hand loads for the most accurate rifle (Rem 700 222) I discovered they measured horribly. This rifle shoots these hand loads 5 shots @ 100 yards into less than 1/2 an inch, typically more like .3s. How can this be?
Thanks.
Matt
 
The bullets tend to center themselves going down the barrel due to the bearing surface of the bullets. The Remington 222 is an inherently very accurate cartridge.

Get a set of Redding Competition neck bushing dies and your concentricity problem will go away.

Think of what might happen if the cartridges/bullets are concentric.

Also, try 19.5 grains of IMR 4198 with a 50-52 grain bullet in your gun. This used to be THE load for BR shooters in 222 Remington.

;)
 
I've got a couple of concentricity checkers, and used them for awhile a few years back. I worried, fiddled, tried to make things better, and was spending more time doing that than learning to shoot better. If you've got a factory rifle that shoots 1/2" groups shoot it, learn to read the wind, and don't worry about concentricity. :eek::eek:
 
Am I understanding you? When you put your loaded cartridges on the Sinclair gage you say that you get very inconcentric readings? Well, just what kind of "inconcentric" readings are they?...... .3" groups sound pretty good to me when chambering bananas!

I have found that most cartridges I put on my Sinclair gages (I use two gages for each load) that give me readings of say minus .004" and less are just as good as the cartridges with "0" readings. In fact, rounds as imperfect as minus .006 and perhaps minus .007 are also just as good on paper that I can tell. It's the minus ..009 readings and worse that I can see the affects on paper, and will use as bore foulers. As you probably know, any reading needs to be halved. So, a reading of minus .004" is actually halved to a reading of minus .002". So, the severity of the readings isn't even as bad as it looks.

Either way, .3" groups are pretty good when reporting inconcentricity.

I've never tried the Reddng competition seater die, but am quite pleased with the Wilson in line seaters.

LARRY'S got the right idea. But, I don't think I will ever change and be able to toss out all microscopic butt examining apparatus. Just my nature I suppose. You too?.....you poor fella.:D
 
Sounds familiar. My 222 rounds, when I was using my original, circa 1959, Pacific sizing die, had huge run-out measurements. I can't recall the dimensions exactly, but, huge. I continued to use this die for a while after I had Hart Rifle Barrel fit a new tube, and in spite of the crooked cartridges, the rifle shot really well. Figuring high run-out can't do accuracy any good, I switched to a Redding FL die, and cartridges now have necks concentric with the body. I can't say the groups are definitely smaller, but, well, it couldn't have hurt. The good groups with the high run-out were FL sized, and had the bullets seated for a hard jam into the leade. Maybe case dimensions are irrelevant if the case doesn't contact the chamber much.

Harold
 
Let's see; we load a cartridge and fire it. The bullet is kicked in the rear by a sudden increase in pressure from 0 to around 52,000 psi in a couple of milliseconds, accelerates from 0 to somewhere around 3,000 fps in that time, distorts by being shortened while expanding to fill the throat, then slams into the rifling is engraved and drawn down slightly, subjected to severe rotational stress, has material torn from it, while heating from hot gases and friction, then it sales free of the muzzle where it is subject to aerodynamic forces, and we are worried about a few thousandths of an inch concentricity because - why exactly? ;)

Yep, I did the same thing - worried about it until a fellow shooter asked to check some of my ammo with his new concentricity gauge. Measured .001" to .0014" and that with old simple RCBS dies and after being neck expanded and fireformed, no neck turning, no nothing. Now I worry about the price of diesel fuel instead.
 
Concentricity

My take is that concentric rounds are never a bad thing. The bad thing is how hard you have work sometimes to achieve good concentricity.

The toughest part for me has always been getting the best possible match between the chamber and loading dies. The expander ball is always an issue in that you can take a piece of brass with .001" neck wall thickness variation and end up with .007" excentricity simply by running it through the standard reloading die and pulling the neck back over the expander ball.

My preferences in dies is usually the Lee Collet die for non-neck turned cases and bushing dies from Wilson or Redding for the neck turned cases.

Another issue in measuring concentricity is that the reading you get from your gauge is in reality TIR which is twice the actual distance the bullet is off center. I think this reading alarms a lot of people, when they should realize that it ain't that bad.
 
Maybe that's why a some bullet lengths and designs shoot better when seated well back from the lands. When pressure opens the neck, they align better before hitting the lead and lands. The bullet isn't in contact with the neck as pressure rises, its floating on a cushion of high velocity gas that tends to equalize circumferentially centering the bullet amid blow-by and turbulence. If they are completely, or almost free of the neck, they self-align.

Maybe this is the same reason that some groups round out better with full length resizing or body bumping, because the bolt face, chamber and bore are slightly misaligned, where the slop allows pressure to realign everything? I have no idea, it just works sometimes.

A good neck thickness micrometer is a good investment, allowing one to know the variance and degree of error. In my case, I neck turn for chamber clearance in some, or use a neck ream die for wildcats that have necks formed from shoulder material in others. The new neck and full length bushing dies allow precise resizing without needing the expander ball, and the precision seating dies have aided accuracy. As has precision brass such as Lapua and Nosler.

All in all, these questions, theories and pet procedures are what make this such a great sport - alchemy, science and mental exercise all rolled into one. That these rifles shoot as well as they do is just phenomenal, as are the shooters and tinkerers.
 
I chased this dog

many years ago when I first started to reload.

Here is what there is to learn from a concentricity gage:

How good is the brass.
How good are the dies.
How good have you set up the dies in the press.
How good is your press operation technique, both sizing and seating.
How good did you lube the brass etc.

If all the above is good then look for 0.0015 on the bullet just forward of the case mouth.

Try this: Check the runout on a fired case out on the neck. Prepare this case and reload it. now check this same case for runout in the same place as before.

Your job will be to determine if it is the brass, dies, setup or technique.

Hint: You better start out with really good brass, such as lapua and be using a competition type seating die.

Enjoy yourself.
 
TIR is not halved any more than your groups are. Total Indicated Runout..
IAW .004" total swing is just that(not .002).

Measuring and reducing TIR produced from your system won't hurt a thing either.
 
mikecr said:
TIR is not halved any more than your groups are. Total Indicated Runout..
IAW .004" total swing is just that(not .002).

Measuring and reducing TIR produced from your system won't hurt a thing either.
Click to expand...




Sorry, but there is no room for compromise or trying to be agreeable as this is a matter of black and white physics; You are wrong.

If for example, a Forster Concentricity Gage was the tool in question, it takes measurements from the case's axis and you would be right.

However, the poster mentioned a SINCLAIR CONCENTRICITY GAGE in particular. It does not measure cases from the axis. Measurements are obtained from the case being rotated on its outer circumference, causing the readings to be doubled.
 
Physics my behind..

We're not talking specific error. We're looking at the combination of numerous contributers to TOTAL INDICATED RUNOUT.
You can't assume for example, that a rise on one side will cause an opposite dip on the other. Oh No.
We're not isolating any specific deviation with concentricity tools.
It is a purely comparative view of all deviations combined. Some add, some subtract from each other.

I understand what you're suggesting. But that would apply only while measuring a single, isolated error.
 
vanib.
They are little bananas. They range from .001 to .009, total.:eek: I just find it odd that they shoot so well. Maybe I will seat them a little deeper and see if they straighten out. Hopefully groups will shrink too. I wonder what the poi will do?
 
About 10 years ago I had a 222 and I couldn't get it to group good,I tried dif powders,bullets,primers,seating depths and I was in my kitchen after reloading some dif loads and one of the rounds tipped over and rolled on a glass cutting board i had, and i couldn't believe what I was seeing:eek:The tip of the bullet was going up and down alot as it rolled,so i checked some of the other ones and they were all like that!So I borrowed a friends comp dies and the gun shot great.I sent the dies back to RCBS and they replaced them,but now I use redding and forster dies and i have a forster co-ax gauge:D
 
concentricity

At lake city if the neck concentricity was less than .005 we didnt worry about it. If it went over 5 we would work on the taper machines. Try to line em up better. That was for M-60 rounds. The 7.62 they shot at camp perry we ran on our best machine tried to get it down to 001 or 002. That was just the unloaded case. Loaded round concentricity wasent my dept. That was loading.
 
Muslmutt,

Seating deeper will not straighten them.

The figures you reported presumably are from one end of the gauge swing to the other, the TOTAL reading not halved !! 1 thou is good, 9 thou is not. You might find that your ammo shoots a little better without the runout.

Mr Axlenut talked about all the forces going on. That is precisely why runout is looked at. The force pushing the bullet into the rifling is so strong that if the bullet is crooked it will stay crooked and be shoved some degree of side on into the rifling making it less well balanced than it was. The whole alignment thing is a lot of what custom benchrest rifles are about. Straight chambers, square bolt lugs, turned necks etc all to start the bullet down the barrel nice and true.

If the rifle shoots OK with banana rounds it just means that there is some other aspect that is limiting the accuracy and not the amount of runout that you have. I bet 5 - 10 thou runout would show up in a benchrest rifle !

Most of the misalignment is probably happening in the sizing operation and some in the seating operation if you are using conventional dies.

If you want straight ammo for a factory rifle get a Lee collet neck die and a Forster or Redding in line seater or better yet a Wilson seater. Given half way decent brass you should have no more than say 3 thou maximum runout.

Bryce
 
Thanks. I realize and agree with most of what has been said. Mostly I am wanting to better understand why a rifle would shoot quite well with handloads that have poor runout. I do find it interesting that good runout would be considered more critical in a rifle with a sloppy chamber. What is up with that?
 
Concentricity

Part of the reason that the 222 family of cartridges seem to shoot fairly well with concentricity problems is the design of the throating. The throating Warren Page came up with has a diameter of .2240" for the freebored section which will tend to center the bullet if the throat and body are allowed to move in the chamber. This results in a rifle that may shoot better with full length resizing than neck sizing with a conventional design neck die. You may be achieving all the accuracy your rifle is capable of by using your current loading procedure.
 
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