Concentricity Guage

[Bolt Bender]

I have the Hornady and the Sinclair. The Hornady can only be accurate if the case head is perfect. It relies on the case head self centering in a cone. The Sinclair has a limitation with small (223 in my case) when checking unfired new brass. The ball bearings are too far apart for them. When fireformed, you can position the case on them and the gage on the bullet, but you have to maintain counter pressure on the cartridge as you turn it. I'm looking for an alternative too.

 

[mikecr]

It's hard for me to understand your troubles there. I measure 223 without issues with my Sinclair.
But I gotta say there is no reason to measure runout on new-unfireformed cases. They cannot be expected straight until fireformed anyway, so there is no useful information in it.

 

[Bolt Bender]

It was useful to ME, in determining why some new Winchester brass did not want to chamber easily in my T/C rifle. It was just a simple observation, not meant to dissuade someone from purchasing it. In that case the case heads were concentric to the seated bullet, but not the shoulder. A number of them had gotten a bit flattened somehow. Maybe the package was even stepped on, or had something heavy placed on it.

 

[BoydAllen]

Years back, I asked someone how straight ammunition needed to be. The fellow that I asked was a benchrest competitor, and he told me that anything better than .002, loaded round, measured on the bullet, was good enough that he could not see any difference on the target. I am pretty familiar with the loading practices in short range benchrest, including that of several record holders, and I do not think that their ammo would necessarily measure at .001 or less, on the bullet. One time I took an H&H to a match, and straightened all of my ammo (slightly) as I loaded it. Some other fellows came over and had me measure theirs. From that, and my other experiences I have come to think that most probably we are looking at ammo that is at .0015 and better, as is mine, right out of the dies. My friend Billy Stevens, once told me that he has figured out how to load ammunition that is straighter than I do, but that he can't prove that it shoots better because of it. Given his credentials, I tend to believe him. There are places for the third and fourth zeros after the decimal , but at the target, I don't think that we can see a difference.

 

[Lazydays]

Years back, I asked someone how straight ammunition needed to be. The fellow that I asked was a benchrest competitor, and he told me that anything better than .002, loaded round, measured on the bullet, was good enough that he could not see any difference on the target. I am pretty familiar with the loading practices in short range benchrest, including that of several record holders, and I do not think that their ammo would necessarily measure at .001 or less, on the bullet. One time I took an H&H to a match, and straightened all of my ammo (slightly) as I loaded it. Some other fellows came over and had me measure theirs. From that, and my other experiences I have come to think that most probably we are looking at ammo that is at .0015 and better, as is mine, right out of the dies. My friend Billy Stevens, once told me that he has figured out how to load ammunition that is straighter than I do, but that he can't prove that it shoots better because of it. Given his credentials, I tend to believe him. There are places for the third and fourth zeros after the decimal , but at the target, I don't think that we can see a difference.

with standard Forster dies in my Co-Ax I can load anything from .222 Remington to 6mm Remington, and hold everything under .0015" TIR without too much trouble. I shoot for .0012" on average, and occassionally see a strait up .001" TIR, but this also not the norm. The norm is between .0012" and .0017" TIR. With Wilson dies and my K&M press I can get down to the .0012" area on a regular basis. But I also have a die set built by Mr. Pindell in .222 that will often do a series of rounds in the .0008" area, and rarely exceeds .0012". I see little difference in group sizes with rounds loaded within .002" like yourself, but will confess that I never shoot anything over .0025" anyway (I'll break the loaded ammo down).

Reason I said 222 thru the 6mm was because I've been having some little nagging issues with some bigger rounds. Last batch of 30-06 I did was in the .003" to .0035" range, and just think I can do better than that! Yet my 270 mag always comes in under .0022" TIR, and will often dip down in the .0015" range.
gary

 

[BoydAllen]

Look at how much your longer cases are being reduced by sizing, and consider a custom one piece. A friend ordered a couple of custom one piece dies from Hornady set up so that with the expander he has .002 neck tension , and without .003, all with the clearance he wants. IMO the reason that longer cases are harder to get straight is that the differences in wall thickness cause a given amount of deflection per inch of case... more inches, bigger curve, more angle on the neck. This is separate from expander ball, die neck ID issues. I did some pressure testing for a tight necked short throated Weatherby, that took one shot per load as far up as I dared. The brass was neck sized with a factory one piece die that just happened to give the right amount amount of sizing with the turned necks. The brass stayed very straight throughout testing, quite contrary to my previous experience with similar dies and unturned necks. The other thing that I noticed was that the fired case would still chamber easily after all that high pressure abuse, probably because I left the body diameters of the reamer stock Weatherby, with the thght fit in the neck and throat only. This is an extreme example of what having no body diameter change does, If I had put that case in a stock FL die, I would have expected it to develop a curve, the amount of which would be in direct proportion to how much the case body diameter was reduced. Using a one piece die, with the neck ID specified so that cases are not pulled crooked by the expander ball will usually give better results than a small die that uses bushings, because the bushing float does not allow the die to do any straightening.

 

[mikecr]

The other thing that I noticed was that the fired case would still chamber easily after all that high pressure abuse, probably because I left the body diameters of the reamer stock Weatherby, with the thght fit in the neck and throat only. This is an extreme example of what having no body diameter change does, If I had put that case in a stock FL die, I would have expected it to develop a curve, the amount of which would be in direct proportion to how much the case body diameter was reduced.

Are you saying the chamber left big clearances in the body area, or small clearances?

 

[BoydAllen]

Relatively large clearances in the body. The headspace was well controlled at the belt, and the shoulder of the chamber only allowed the shoulder of the case to blow forward .006 instead of the .021 that the factory chamber allowed. The Shoulder and front of belt diameters were as per factory spec, from a book that I have.

Some time ago, I friend had a 6BR that had been chambered with a reamer that was designed for Remington brass. He then decided to switch to Lapua, which required some neck trimming, and even with that, the back of the chamber was too small, so the gunsmith used abrasive material to increase the diameter of the body of the chamber enough that Lapua cases would chamber without any problems. There was room, but only just enough. When my friend got the rifle back, he found that he could not load to the expected levels without getting pressure signs, notably a tight bolt lift. At that point he sent the barrel to another smith and had it set back and rechambered with a reamer that was designed for the Lapua brass, and which had more clearance on an unfired case. With that chamber, he was able to make excellent velocity without any problems.

When you shoot a warm load, the chamber expands, both the steel of the barrel, and the brass of the case. As the pressure eases, the steel snaps back to its original position but the brass finishes slightly larger than it started out, and if there was not much clearance in the first place, the bolt will be tight upon opening, but with more clearance, the brass' snap back dimension will be smaller than the chamber, and the bolt will open normally. I took this experience into consideration when designing my friends .300 Weatherby reamer, and it worked out really well. We took that brass well above the book, and a about three .grain steps above where the rather large Mk IV ejector showed a bright spot on the case head, to the point where the belt changed in diameter a second time. After we had finished our notes. I picked up the case, that had been neck sized only, and it chambered easily. Do not load as hot as I did for this test. You might not get away with it, and the results could hurt someone.

 

[mikecr]

Sounds just opposite of what I see.

This is what I think; No matter the clearances the case will obturate to expanding chamber walls. At high pressure the brass itself is relatively resistant to this as tin foil -but with springback. Thicker brass (of the same hardness)springs back more than thinner brass.
So with big clearances, brass expands to a point of yielding in size, becoming thinner and losing some springback, and now more likely to be trapped into interference fit with restored chamber dimensions.

I watch this happen near webs with testing to determine MY max pressure point(that point where FL sizing is required).
As I go up in load pressure the web ring(from new) will expand ~.0005" and level off. It has yielded that much at that point and is springing back to that new dimension. As I go upward in pressure I'll see a point where the web ring step changes to ~.001+ and will steadily continue to increase with pressure. This is no longer leveling off but is runaway yielding.
Now the chamber doesn't yield(it better not), so at some pressure the yielded brass fits with issue. It no longer springs back enough to clear chamber walls.

With my 6.5wssm, I set .001 total clearance on every new case dimension. This tight clearance approach is often criticized, however, it has not, and by now I know will not, present an issue for me. Yes, I can run pressures high enough to cause extraction issues, but this would not be because of chosen clearances. It would be because of irrational pressures, and/or insufficient barrel steel around a chamber.
With my tuned load(producing 3030fps with 139Laps while just under SAAMI max), that .0005 of web ring has held without ever sizing case bodies. I will never have to FL size.

Why opening clearances seem to help with extraction for you, I don't know, unless the pressures are so high that you're merely managing a broken condition. That is, easing extraction -with an interference fit.
That an unsized case comes out of a smoking chamber straight is pretty well established as the only way to get a case straight. So that part makes sense.

 

[BoydAllen]

I said that we tested to high pressures, not that the plan was to load to that level, but we do generally load to levels that require FL sizing, as do most shooters that want to get everything out of their rifles that can reasonably be achieved. In the much smaller caliber that dominates short range benchrest, this situation has produced a well established trend to using custom FL dies that do not make brass crooked, and only move it a little. As a part of this project, we had Dave Kiff make a FL die reamer, that sits on the shelf, at this point unneeded. The owner of the rifle has a number of cases, and only shoots in preparation for a hunt, and for a hunt, which is not very often. The new barrel was blooded. The rifles owner took a high shoulder shot on a good sized elk at around 600 yards and dumped him on the spot. The reason for the unusual testing was that this was a chamber that was clearly out of factory spec. The throat allowed seating his chosen 180 grain bullet to be seated into the lands, with rounds still able to fit the magazine, and it had a tight neck chamber, that required that necks be slightly turned. Because of these features, I wanted to get a better than normal idea of what would happen to pressure as loads were increased. As it turned out, by the time we stopped, we were a grain and a half over the book, so there would be no danger if book loads were used. That is what we were looking for. As to your situation, I am not saying that every one else should follow this, I was just recounting an experience. Obviously you are taking excellent precautions by monitoring head diameter. In our case, we saw a move in belt diameter on first firing, with a load that was otherwise clearly safe, and continuing on, there was no further movement until the last load, where we stopped, never to return. This was for a long range hunting rifle that the owner had specific goals for. Personally, I would never set up a chamber for a hunting rifle, with a tight neck, close perhaps, but not tight, but I did like the idea of having the option of loading rounds that were slightly into the rifling in the magazine because I have often found advantages in accuracy at those seating depths. Even that would not be so much of an issue for most use, but this was to be a rifle for an out of state elk hunt, on a ranch where long shots were the rule.