Home Forums Reloading Big Game Rifles I want to measure case necks, need advice.

I find that my run of the mill brass is imperfect enough that there are usually some exterior cutting skips. If one was rich enough and could handle the cost of rejects, he could probably assemble a batch that did not exhibit such patterns and were therefore closer to perfection. I have one set that way for only one rifle, a 22-250, where my initial brass collection totaled about 600 rds. That batch had primer pockets worked up, were fired, trimmed, reamed/turned, and weighed. I took the 100 closest to average weight and sorted them from lightest to heaviest, etched on a number, put them in order in my ammo box. Any increase in pressure, if there is any, will be moving consistently and only slightly upward as I progress through that batch. Talk about anal? Can't afford to do that with my other units.

As to doughnuts: I would assume that if we full length resized and did indeed move our imperfections to the interior, running the reamer well into the cartridge would remove the doughnut.

I think the issue with doughnuts is 1)an inconsistent grasping of the bullet, and 2)perhaps some disruption of gas flow.

I neck size only, and do run my reamer deep. My thoughts are that the fired cartridges fit into my chamber and that if there is doughnut on the exterior surface, it would be due to a faulty chamber. If it remained on the exterior in that instance, it would be a non issue.

I tend to use mid weight slugs, and with the exception of my Weatherby's, try to get near the lands. That being I don't think I would ever have a doughnut grasping a bullet. Most bases don't make it down through the full length of the neck. Disrupted gas flow maybe.

Have good one, 1Minute

I know I have experienced this, and don't folks do this to have concentric support in the chamber neck area: only resize the neck about 80% down. After slipping only part of the neck in the bushing, a doughnut appears where the brass did not enter. It disseapears after firing. Is that the same flavor of doughnut as a neck turned doughnut?

No, the dreaded donut is where a ring of thicker brass migrates upward from the body/shoulder of the case into the neck wall.

Ahhh, different flavor. Thanks mathman.

Only problem with that is that the donut will NOT be concentric. The high spot will cause the floating reamer to "float" to the path of least resistance. The back side of the reamer can then stovepipe the interior of the neck and permanently skew the bore of the neck making the whole effort a waste of time.


Grip on the bullet will force the donut to the exterior. Grip would probably be the same. Even if it weren't, how much difference will there be from extra pressure and grip on one side from only a small fraction more contact and how much does that affect grip, pressure and accuracy? Not much in my opinion. I therefore respectfully disagree with that concept.


How can a brass problem, a donut, be due to a faulty chamber? And if an uneven protrusion forced to the outside of the brass on bullet seating skewed the cartridge in the chamber, it would cause a non-concentric seating of the cartridge in the chamber.

Again, if the donut is uneven as it is almost sure to be, the reamer will take the path of least resistance and possibly stovepipe the bore of the neck.

Mathman: Yes, that has been the explanation I've most often seen. Flow from the shoulder to the neck shoulder junction.

In a factory chamber where there is significant clearance around the neck, wouldn't the following sketch apply



where the sizing of the neck would negate the contact of the do-nut on the bullet?

Do-nuts have only been detectable to me when I have a tight neck chamber with .003" clearance so that a fired case inside neck diameter is already tight on the bullet. Then you can slide the bullet in and it will stop at the do-nut. But on a factory chamber with lots of clearance it is impossible to detect, unless some of you have found a way. The do-nut must still be there but the added clearance would make the inside neck diameter large enough for the bullet to slide past it. In that case it wouldn't matter anyway cause it will never contact the bullet, unless sizing the neck smaller sizes the do-nut down also.

Make sense?

Bobski: Yes! I'd agree the conventional donut is typically not a chamber issue. It's brass flow from the shoulder to the neck / shoulder junction with repeated firings and it's an inside the cartridge problem.

As to "floating" reamers.... Yes! I again agree that one will always have issues with such a system looking for the path of least resistence. I for one would not use such a tool.

Regarding faulty chambers, reamers wear out, wear inconsistently, and experience all kinds of abuse and damage. If any event is even remotely possible, it can and likely has happened. If indeed such an issue did arise, it could be partially treated by indexing ones cartridges to make sure they were all consistently oriented in ones chamber. There may still be a bullet flight issue, but if it has the same effect from shot to shot, we can perhaps live with it. Some bench folks do go this route just to cover their butt. They may have an unrealized problem, or they may not. Either way, a consistent approach always helps.

The point that I perhaps did not clearly make, was that the typical donut fix should be addressed from inside the cartridge as opposed to routinely cutting into the exterior of ones neck/shoulder junction for a problem that might not even be be there yet.

Varying neck wall thickness within in a single cartridge will certainly affect bullet/bore alignment if the high side has enough dimension to touch the chamber neck. Secondly a thicker side will exhibit less flex in the sizing/seating operations and induce bullet runout. Both of those are bad things for one seeking perfection. I try to keep my bullets seated within the area of a cartridge neck that has been both reamed and turned. That portion of the cartridge is a least as consistent as I can make it. Any portion of a donut that is not removed by the reamer though, can still have some influence on gas flow. That, I will just have to live with.

Lastly an inconsistent amount of grip on ones bullets as we progress through a series of cartridges will mean more or less pressure is needed to initiate bullet travel. That variation will also help open up ones group. In this instance, chaos theory may apply in that very subtle differences at the beginning of an event, can have substantial impact on the final outcome. Have a good one, 1Minute

Woods: I'd agree that donuts are less of a problem in a loose factory chamber. In many instances, the tighter we make our tolerances, the quicker things can go to hell.

Sort of like a sloppy AK47 that can come out a wet sand bucket and keep firing. A precision American made semiauto, however, will quit nearly every time.

If both are kept spic and span though, our unit is the more accurate of the two.

I think we agree, especially on the issue of the donut.

Our only issue is the impact of the varying contact and "grip" on bullets and how much a group is thereby affected. I question there is "substantial" impact; I think it is minimal on group size, especially if necks are regularly and consistently annealed. Cheers.

Good illustration Woods. Makes sense except for the fact that donuts are not necessarily "small" and if flat base bullets are seated into the shoulder area they WILL cant the bullet. Usually boat tail bullets don't quite get to that point, but they can as well depending on chamber configuration.

Guess I've had my share of donuts, especially in cases for wildcats where the thick body of a parent case becomes the neck for the new case. The very thick body brass is left in the shoulder of the new case and eventually becomes a very intrusive donut.

While out for a drive last evening I came us with the concept for the ultimate magnum spiffy super excellent competition grade neck reaming system that might even do away with the need for turning. One would deprime his cartridges with a universial deprimer, run a cartridge into a neck sizing die, and then ream while the cartridge was still fully within the die. That would lend near full support to the exterior of the neck. If we did away with the threads in the top of the sizing die, sized the shank of the reamer to precisely fit that hole, the reamer would be extremely well supported and minimize potential wobble or lateral movement. Now to assemble my machine shop. Patent pending. 1Minute

That's what is called a reamer die. I got mine from RCBS years ago and they may no longer be available since they stopped their custom orders but it would be worth a call if you're interested.

The reamer is a close fit in the boss at the top of the die. Works well. I don't have picture but will take one and get it possted in due course.

Tried the RCBS site and there are no pictures available and they only list one. They do have something called a Pilot/neck reamer and only one reamer die listed now at their site: http://shop.rcbs.com/WebConnect/Mai...Type=0&searchDescription=reamer+dies

Maybe C-H or Redding have them. They aren't cheap.

Here's photos of reamer die. This one is a FL die on left for comparison, reamer die and reamer on right of it.



Reamer die with reamer in boss as when reaming inside of neck. Incidentally, the teflon block in the background used for support, is drilled in various calibers. That's what I use to "straighten" eccentric necks when checking and verifying concentricity of reloads.



The tolerances are pretty tight between reamer and boss. I've never measured the movement of the reamer end but it's minimal. Another shot of reamer and die.

Sweet! Will have to look into it.

Lee mad something similiar many years ago. They still might make them.

I have one, in .30-06, that I purchased about 25 years ago. They are designed to work without neck expanding. The case is pressed into the die, then the reamer goes in through the top of the die, which aligns the cutter, then the cutter reams the case so that the inside neck diameter is about .001 smaller than the bullet.

The bullet is held in place by the tension of the bullet expanding the neck .001".

It works, or at least it reams the neck, but I have never tested one of the loaded rounds for run out. I have also never measured the neck wall thickness to determine if the reamer centers the hole in the neck.

25 or 30 years ago, I didn't even know about uneven neck wall thickness or concentric ammunition.

Reaming dies seem to be a thing of the past, at least in a preliminary search I haven't found any on the Lee, RCBS, Redding or Forster websites.

But, with the Forster reamer http://www.forsterproducts.com/store/detail.aspx?ID=13



which has the following description:

"Thick case necks can cause high chamber pressures and flyers. The Forster Neck Reamer mounts in the cutter of a Forster Case Trimmer in place of the pilot and removes the excess brass from the neck walls. The Forster Neck Reamer is manufactured from high grade, wear-resistant tool steel and ground .0025" to .003" over the maximum bullet diameter. The staggered tooth design cuts the brass smoothly without chattering. Photo illustrates three different sizes. Choose size from reamer number list below.
$24.00"

you could ream out the neck .003" larger than bullet diameter and get rid of a do-nut that way.

For example I have a 6.5 rem mag with a .292" neck size. Doing the math .292"-.003"=.289"-.264"=.025"/2=.0125" for neck thickness. Then after I fire the case the reamer should just fit inside and not take any or very little off the inside of the neck brass until it gets to the do-nut. Then, bye-bye do-nut.

The questions would be:

Will the reamer follow the channel of the inside neck and not stray off to one side?

Would the reamer fit in my hand turner or would I have to buy a Forster hand crank trimmer?

Also, when you fire a case the brass forms to the chamber and the outside of the neck is smooth and concentric. It is after sizing that the imperfections get moved to the outside of the case. Theoretically you have gotten rid of the variations in neck thickness by outside neck turning already, but would whatever are left of the variations in neck thickness cause a problem with the reamer as far as getting off center and taking brass off where you don't want to?

Anybody doing this?

I think I've tried every which way to get rid of donuts. In tight necked BR cases I always used to end up throwing them away and starting over. About the time I gave up BR there was a tool, a reamer of sorts, that became available to clean the donut out from the inside. Forgot who made it and don't know if it was successful as that was about the only thing I didn't try. It had the facility by its design (something like a hook on the end of the reamer,) to get the donut and a bit of the shoulder from the inside.

The reamer will always find the path of least resistance unless the brass and reamer are both held rigidly and backed up. The offset can be minimal or significant, depending on the imperfections of the brass.

Reaming with the Forsters, of which I have many, some of which are "custom", you could never completely do away with the donut on its high side. There's almost always a high side. The brass springs out when you ream, then springs back. You were successful sometimes if the high side was minimal, and many times not.



The Forsters don't handle well in any hand turner. Mine are round with a single small flat on one side of the end. They are made to be used in their trimmer where you can get enough pressure on the allen screw to hold them when they start cutting. In a hand held there is no simple way to hold them from spinning when you start the cut.



Yes, it's those imperfections of which we speak; the reamer will follow the path of least resistance.

I've tried turning the outside after expanding the necks and donut after FL sizing (thereby moving the donut to the outside,) and again the brass springback still leaves vestiges of the donut somewhere. If you don't turn the outside you then have a neck with uneven thickness at the base of the neck. In hunting rifles with .002" clearance on the neck all the way around it might not make much difference. Where you truly notice this is on the non big game rifles. You can usually figure out something on rifles with relatively loose dimensions in the chamber but if we're talking "perfection" and trying to shave tenths on your groups, I'd like to find a way. I think I've tried everything, except that gizmo mentioned above, and I never have. Lord knows I've tried.

Thanks bobski

The Forster hand held neck turning mandrel has a flat spot on it also where you set a screw to hold it in place



I have 3 guns with tight necks, the 6.5 rem mag (.292", a 280AI (.313") and a 338RUM (at least I hope it will be tight at .367", I'm waiting on it now). I think I will give one a try. If everything could be set just right it could do a good job not only on the do-nuts but also as a fine tuning of neck thickness.

I think I know what you're thinking as far as fine tuning neck wall thickness. Try it but I think you'll be disappointed. You'll quickly see the the necks don't all spring back from either firing or reaming quite the same amount and you'll end up with varying neck wall thickness.