Concentricity tools and chamber postion of cartridge??

[kraky]

Looking for input. A friend is building an 800 yd range and I want to prepare for some longer range shooting. I had a rcbs v block runnout checker and just picked up a new hornady unit that has a "correcting" screw to push the bullet in the case.
The new hornady tool supports the case from the tip of the bullet and at the base. It basically leaves the case unsupported.
The situation is after alot of spot checking past loaded ammo the hornady cannot find anything I've loaded to be over .003 tir. Yet I can find some examples with the rcbs that are .005-.006".
I've even seen .006" on the rcbs and can see the bullet wobble...yet the same case on the hornady shows .001".
I called hornady and they say their idea is the best because the bullet is in line with the center of the case and the casing imperfections don't matter.
SO I GUESS my question is....exactly how does a cartridge lie in a chamber?? I try to bump shoulders no more than .003...usually .001-.002. If I do this and chamber the round does it sort of "lift" up in the chamber and center via the bolt face and front of chamber....or does it lie at the bottom.....or does the extractor hold it at an angle in the chamber anyhow??

 

[rick smith]

I have not tried the Hornady unit. I had a RCBS unit and sold it, didn't like the unit as a whole. I now use a NECO and a Sinclair. Both of them agree on runout. I have the NECO set to measure bullet runout and the Sinclair for case runout. If you roll a loaded round on a good flat surface and see bullet wobble but the Hornady indicates little to none, I would expect a faulty unit or, sorry, operator error.Rick.

 

[kraky]

No operator error. There are other units out there that support the cartridge from the tip and at the base. Basically it "hangs the cartridge" in mid air. I think one of the problems is you are measuring so close to the point of support...but apparently other makers think this is ok.

But...I'm interested to see what others think is the result of chambering a case with close headspace anyhow. Does it lift the casing up somewhat off the chamber anyhow??

 

[kraky]

Here's the tool and how it works....

 

[Desert Fox]

I totally disagree with Hornady statement! If the case is not concentric to the bore will then, so is the bullet. The first step is to check for case runout. This includes neck turning if necessary. The loaded round is then check for runout. I like my load to be within .001" to .002"

I use the Holland concentricity gage as shown in the picture below. It's one of the best there is. If the case body is not round, It'll show in the dial. Those case are either discarded or use for load developement. I use Lapua, Norma, Federal and Nosler brass. Brass thickness and concentricity is pretty uniform throughout on those brand mentioned.

SO I GUESS my question is....exactly how does a cartridge lie in a chamber??

If your chamber is concentric and the bolt face is squared, Theoritically, your cartridge should be in the center of the chamber... assuming you're using a once fired and necksized only case.

 

[Ol` Joe]

My opinion is the case should lay straight and in line with the bore if concentric, but..... There has to be a few thousanths of tolerance slop for the cartridge to freely enter the chamber that can allow it to move to a side. The necks if sized and turned to fit the chamber may have more effect on how concentric the case is to the bore then the case body. Then too the ejector is pushing the back of the brass to one side trying to knock it off the bolt face so that is another factor..... don`t know how well they line up for sure.

 

[rumshooter]

What a humbling queston, really makes one think. As the case head spaces off the shoulder or the belt, depending on the type of case design, and the fact that an interupted fit is not acceptible, then there technically has to be some clearance in the chamber. How much affect on accuracy it has is probably not possible for most of us to know but I do the best I can to promote concentricity and repeatability. First trim the necks square and to length then turn the necks to achieve concentricity. When you shoot these the first time do not be concerned with accuracy as it will come when shot the second time. At this point your main concern is to align the cases with your particular chamber. Now check for bullet runout at the ogive supporting the case at the base and the neck. This about as good as you can do for concentricity. Be sure to neck size these cases only so you do not ruin all the work you have put into making them concentric.

 

[kraky]

Been thinking about this a little more. It would seem the best place to rotate the case against a v block would be right at the point where the sizing die quits. It would be my opinion that this area of the case will swell about .003-.005 after a few sizings. This area might even slightly hold the case up off the chamber.
Also...just got this months shooting times. They did some shooting of factory ammo with a railgun. Concentricity didn't seem to matter much. At least in that gun and at 100 yds. The worst runnout ammo .019" finished in the middle of the pack. The best runnout finished last. The top performers had .004-.005" runnout. Apparently the combination of bullet, powder and seat depth had more to do with success in this test.
The following is a pic of their results. The first column is TIR, the second is variance of seating depth. The rest is easily seen.

 

[rick smith]

kraky, after answering your post earlier, I started thinking about the different types of bullets and measuring their concentricity. On the NECO the point of the bullet is in a small holder and held by one V-Block at the base of the case. The Sinclair has two sets of balls as the case support. I tried some Noslers, Sierras and the run out was the same on both my gauges. However the Berger VLDs were quite different The Sinclair showed 0.001 or less for the 300Rum cases loaded with the Bergers. The NECO showed 4-5 thousants for the same cases. Rolling them on the counter top and looking didn't show any bullet movement. I found that the tip of the Berger bullet bottomed out in the bullet support on the NECO allowing the tip to have too much movement as you rolled the case. Removing the bullet support and using two v-blocks on the NECO solved the run-out. Next I will uniform the tips of the Bergers to see if that will make any difference with the NECO bullet support. Interesting problem.Rick.

 

[kraky]

Rick...for what its worth. The hornady unit doesn't really hold the bullet at the tip. The "cone" the tip of the bullet goes into is tapered and it hits the bullet down from the tip much like a seating stem on a seating die.

I got to thinking about the bulge left by the seating die as possibly the BEST place to hit the case with a support on a tir gauge. My reasoning is I've seen how especially on belted mags the dies leaves a bulge. I even had an experience a year ago where ammo I loaded for my '06 wouldn't chamber in a friends gun and it "stuck" right at the stopping point of where the die stops. I figure in my gun that bulge has got maybe .0005" clearance in my chamber. Its actually a point on the case that is not only NOT RESIZED during fl sizing but actually increases in diameter over and above a virgin case.
Wouldn't it make sense that would be the place to support the case when taking a tir measurement?? And I don't know of any gauges that give you adjustability at the rear v block to do so?

 

[rick smith]

The NECO's bullet suporting holder is also cone shaped. Ran into the same problem with seating the Berger's in a Redding competition seating die. The tip of the VLD hit before the "cone" touched the bullet. Contacted Redding about the problem and sent them samples of the VLDs They now make stems for the VLDs. If the bulge is concentric on your cases, it would not matter where the case was supported. The NECO allows you to put the case supporting v-block anywhere along the case. I move it according to the length of the case. The loaded case needs a stop at one end or the other, Sinclair uses the end of the case, NECO uses the bullet tip. Without a stop, the case can move right/left as you spin the case. That will allow the indicator to move right/left on the bullet giving bad readings on the dial. From Desert Foxe's picture of the Holland unit, it appears to have a stop at the rear of the case. The Sinclair unit is very similar to the Holland unit. I feel that better measurements will come from a gauge that supports the case at two points with the bullet free to move. That totally removes the bullet tip from the equation.Rick.

 

[30-338]

Kraky, Here a picture of the Neco
http://www.neconos.com/details.htm

Here the picture of the Sinclair
http://www.sinclairintl.com/product/557 ... ity-Gauges

I've have the Sinclair

Here is close up picture of the Holland
http://www.longrangehunting.com/gearsho ... gauge.html

The Holland you can move the pins so as with the other you can adjust for case length.

 

[elkeater2]

I made up my own concentricity checker using hardwood, Sorry, I'm not near home so don't have any pics. I studied the features on all the commercial ones.
I made adjustable stops to accommodate different length cases. Tried different configurations of v-blocks, and made them infinitely adjustable in relation to the base stop. Made the dial indicator adjustable to any point on the cartridge. It all works for me, and allows me to support the cartridge/brass anywhere I wish.
There are all sorts of checks and experimentation that can be done, like taking a fired case through a full cycle: Noting and indexing the case for rotation position when fired, then checking. Decap and resize, and check again. Then seat a bullet and check the whole thing.
If the case measures true when supported at the web and various places up to the shoulder, then I check for neck run-out and bullet runout at various places.
I have learned I have more runout problems with cases that are overdue for annealing as there is more pressure involved to seat bullets. The necks and case mouths need prepped consistently, lube for inside necks needs to be uniform and effective if using standard expander ball sizing, etc.

I think what I need now is to set up my $30 digital fish scale(accurate to 1/10 oz.) to measure bullet seating force!! Does that equate to "neck tension"?
Elkeater2

 

[Antelope_Sniper]

Elkeater, I like the way you think. I tried to make my own as well, but couldn't mill the V smooth enought with my router. When I get a chance I'll pick up a machinest V-block, and my rig will be complete.