Best For Concentricity.......Turning or Reaming Necks??

[dariof]

Most folks are turning necks for concentricity.

But why wouldn't reaming the inside of the necks work better? The inside of the neck is what holds the projectile, not the outside of the neck.

So, which is better for concentricity.......neck turning OR neck reaming????

 

[TommyAtkins]

Bullet concentricity before it is chambered is dictated by the die that installs the projectile. The necks are turned to keep the bullet concentric to the bore and to insure friction is consistant 360 deg around the bullet. Neck reaming will make a perfect diameter in the neck but so does installing the bullet.

 

[M40_A1]

Turning the necks makes the neck walls uniform. Uniformity helps to achieve concentricity. I never understood the benefit of reaming, so perhaps someone could enlighten us on that.

 

[dariof]

Turning the necks makes the neck walls uniform. Uniformity helps to achieve concentricity. I never understood the benefit of reaming, so perhaps someone could enlighten us on that.

I hope those with the knowledge will chime in here! I am confused on this issue as well.

 

[ArmyJerry]

release is dependent upon consistent release of the bullet from the neck, get a K&M and ream and turn at the same time. My limited experience is that the Lee Collet Die combined with a Foster micrometer seater die is a great tool for egocentricity of projectiles in a properly turned case.

 

[ZiaHunter]

Turning the necks provides for uniform neck wall thickness which in turn leads to more consistent neck tension. In addition by using bushing dies eliminates the need for the expander and provides greater control over neck tension. The two major contributors to runout are non uniform neck wall thickness and the expander being drawn through the neck while sizing. The only time I use inside neck readers is to remove doughnuts.

 

[pjparker]

What Zia said.

Adding to that is that neck reaming will not make necks concentric. You must outside neck turn to make neck wall thickness concentric.

Paul

 

[rockier]

ZiaHunter, One question for you. If you could rim the inside of the brass and make it the same thickness as trimming. Would that in turn be the same results to make the brass nick the same thickness?

On that note I have not seen or read the real reason why one would do one over the other if the results are the same.

Can someone explain in more detail.

I have been confused on this for a long time and the information on this site has been great.

Thanks for all the knowledge you guys give us.

 

[pjparker]

I will try to expand on this and Ziahunter may be able to do a better job than me, but here goes:

Neck reaming is primarily used to reduce the thickness of overly thick neck wall encountered when forming cases from other caliber brass, or for removing donuts which have become excessive. It is done on fired brass prior to resizing. The reamer will follow the ID of the neck, and the result will be a thinner neck that is still not concentric.

Outside neck turning is used to true up neck walls that are not concentric. It is also used to thin neck walls to fit a custom tight-neck chambering and also have the neck walls concentric.(Think custom Benchrest rifles here). It is done on fired and resized brass on a tool that has a caliber specific tight fitting mandrel. Since the mandrel is a stationary reference point for the cutter to index from, the cutter will cut more from the thick side, less from the thin side, leaving a concentric neck wall that we all are seeking.

The two operations are not the same. The results are not the same. The reasons for using one or the other are not the same, although could be seen as being very similar to some.

Google is your friend. Neck turning vs neck reaming will deliver you plenty of reading material on the matter.

Paul

edit: Wilson Trimmers are the only tool I know of that will neck ream and correct neck wall runout. The case to be reamed is held in a cartrige specific holder, clamped down on a rail and the reamer is turned into the neck for a nice, clean, concentric neck. The case holder is like an external mandrel holding the cutter and the center line of the case in alignment with one another keeping the reamer from following the ID of the neck, cutting true to the centerline. Just running a reamer into a case neck with a standard trimmer setup will not provide this kind of alignment.

 

[Mad_Charlie]

Mr. Parker is correct, reamers are used to SIZE a hole and make it round.
Reamers will not relocate a hole, they will follow a hole, but it will be round and to size...

 

[rockier]

You have a lot of great points in your answer pjparker. Thanks

Here is what I have got out of it.
1. Concentric means – having a common center point. I think this means that any two points from a center point is concentric. An oval has this and a circle.
2. Pjparker – “Wilson Trimmers are the only tool I know of that will neck ream and correct neck wall run out. The case to be reamed is held in a cartridge specific holder, clamped down on a rail and the reamer is turned into the neck for a nice, clean, concentric neck.” This meats the concentric meaning.
3. Reaming is to remove donuts that form inside of the brass. Why do we care about this problem?
4. Reaming is to size the inside of brass to make it a different caliber.
5. Turning or trimming will make the brass walls the same thickness for the same tension on the bullet and will make it concentric to the center point but not necessarily round. Both pjparker and Ziahunter refers to this point.
6. Reaming and turning are not the same. Agreed, one is inside and one is outside. May make the same tension or may not.

I hope this is right and I did not miss something from your response.

Now the question is how does this helps you’re shooting at 100 yards verses shooting at 1000 yards?

Does the nick length have a play on the tension on the bullet too?

I have read this is only important if the gun barrel is a custom made barrel or you are using the brass for a different caliber then the caliber of the original brass. Is this correct?

Mad_Charlie, Reamers out there you are right but if I use a lathe and ream or turn the inside it will change the hole or relocate it and make it concentric to the center point of the brass. This does not make sure the nick thickness is the same. It could if the outside is concentric to the center point too.

 

[M40_A1]

Who cares if the hole is round if the neck walls are not consistent? Who cares if the hole is concentric to the center line of the case if the geometry is changed as soon as you put it through a die?

Unless you use a perfectly centered expander plug, the "hole" will never be concentric if the walls are not consistent, and even then the difference in the wall thicknesses will cause the brass to spring back inconsistently, so the hole will no longer be concentric to the axis of the brass anyway, let alone "round"!

And if you use bushing dies without turning, the outside may be round, but the inside will be oval and off center.

IMO, if you don't neck turn, practical concentricity will not be achievable. A reamer will make a nice round hole, but it won't stay round if you don't also turn. OTOH, turning alone and passed through a proper die will achieve the desired results of concentricty AND even neck tension (assuming proper annealing and quality brass).

Brass is turned to a reference point, i.e. the mandrel. Reaming* is usually self-"centering" to the geometry of the hole as it exists while reaming.

*A reamer previously mentioned (Wilson, by pjparker) does seem to be referenced to the outside of the neck. That is the only type of reaming set up that makes any sense to me.

 

[dariof]

Who cares if the hole is round if the neck walls are not consistent? Who cares if the hole is concentric to the center line of the case if the geometry is changed as soon as you put it through a die?

Unless you use a perfectly centered expander plug, the "hole" will never be concentric if the walls are not consistent, and even then the difference in the wall thicknesses will cause the brass to spring back inconsistently, so the hole will no longer be concentric to the axis of the brass anyway, let alone "round"!

And if you use bushing dies without turning, the outside may be round, but the inside will be oval and off center.

IMO, if you don't neck turn, practical concentricity will not be achievable. A reamer will make a nice round hole, but it won't stay round if you don't also turn. OTOH, turning alone and passed through a proper die will achieve the desired results of concentricty AND even neck tension (assuming proper annealing and quality brass).

Brass is turned to a reference point, i.e. the mandrel. Reaming* is usually self-"centering" to the geometry of the hole as it exists while reaming.

*A reamer previously mentioned (Wilson, by pjparker) does seem to be referenced to the outside of the neck. That is the only type of reaming set up that makes any sense to me.

This is the direction I was leaning from all the reading and 1,000 yard shooters I've spoken to.

Lapua brass
Turn it....K & M turner, and check concentricity with my Sinclair gauge
Redding S type bushing dies....lose the expander
Forrester micrometer seating die
Forget the reaming unless a donut appears

 

[pjparker]

Rockier

Just to clarify a couple of your points:

We care about removing the "donut" of thicker brass that forms at the base of the neck of a case because it is rarely the same amount from case to case and it plays hell with neck tension if bullets are seated deeply enough to encounter this restriction.

Reaming does not, in itself, make the case a different caliber. It is commonly just one of the steps required when forming brass to make it a different caliber. An example of this would be forming 6mm BR Remington from a .308 case. The neck of the shorter 6mm BR would be formed from the body of the longer .308 and without reaming, the neck would be too thick to be usable at all. Of course, there is no need to go to such extremes since quality 6mm BR brass is readily available - this was just an example.

Neck length must be kept short enough to not jam into the face of the cut in the chamber and "pinch" the case to the bullet. Published trim-to specs keep you safe. varying neck lengths can contribute to varying neck tension, so just keep 'em as close to the same as you can.

At 100 yds with a factory rifle, there may not be much gain for the effort. At 1000 yds EVERYTHING matters.

Paul

 

[rockier]

Thanks pjparker for clarifying this for me. Your help has been great. It does make more since.

I am looking in to shooting long range computation and the guys there talk about this stuff and I was just wanting to know the reason they do all of this stuff to the brass. I also want to know what it is doing to the projectile at ranges of 1000 yards and if it even made a deference at 100 or 200 yards.

M40_A1 I am using the Redding S Type dies. Thanks for the information.