Inside or Outside

[WildRose]

Help with neck trimming.

I'm going to have to purchase a good bit of 7LRM brass or else neck down my own .375 Ruger brass to make my own for the 6.5LRM.

Any way I do it, this will require neck turning.

As I look more and more into it I'm torn as it's looking like outside turning is the most common method with the inside reaming being the more precise.

Any downside to the internal reaming vs external trimming?

Thanks.

 

[Rich Coyle]

The inside reaming can only be as accurate as the centering in your die.

 

[WildRose]

The inside reaming can only be as accurate as the centering in your die.

True but then that's true for both.

In inspecting the necks though of thousands of rounds over the years whether it's from firing or the manufacturing process it seems to me that the thinning is generally occurring on the inside of the case and therefore after proper resizing and trimming reaming would seem to me to be the most accurate and consistent way to get uniformity.

This is however kind of new ground for me so I'm hoping some of the experts on the subject can point me in the right direction.

Looking at the various reamers I wish they were essentially reversed so that the pilot entered first and worked similar to the Lee hand length trimmers with a long shaft, pin at the bottom for the flash hole with the cutting portion still up in the neck rather than relying on cutting as it entered.

I'm thinking a quick call to PT&G could take care of that for me and I could set it up then to run on my case trimmer as just another tool.

https://ads.midwayusa.com/product/3...TT5VnVJ4ddMFTdUmGztnIzRt4A1TbVcRoCfNgQAvD_BwE

 

[sedancowboy]

Most precision shooters use the outside turning method to remove brass from the neck as do I.
Outside turning will make the neck thickness more consistent than inside reaming. When you run a mandrel into the neck that pushes all the inconsistencies to the outside and then the outside turner is able to remove them and the neck thickness will be the same all the way around. In other words it trues the neck wall to a consistent thickness.
If you ream the inside then nothing controls the outside as you push the reamer into the case. so the neck thickness variances are still there.
Sinclair, K&M, and 21st Century all make good outside turners.

 

[WildRose]

Most precision shooters use the outside turning method to remove brass from the neck as do I.
Outside turning will make the neck thickness more consistent than inside reaming. When you run a mandrel into the neck that pushes all the inconsistencies to the outside and then the outside turner is able to remove them and the neck thickness will be the same all the way around. In other words it trues the neck wall to a consistent thickness.
If you ream the inside then nothing controls the outside as you push the reamer into the case. so the neck thickness variances are still there.
Sinclair, K&M, and 21st Century all make good outside turners.

Ok, I kinda get that. I also see that pretty much all of them make the inside reamers as well thus the confusion on my part.

What I see is that we do all of our brass working from the outside thus pushing the eccentricities inward.

Maybe for the ultimate in consistency I should do both since it should only have to be done once if it's done right to start with?

I'm either building a better mousetrap here or just making it far more complicated than necessary.

Like I said though, this is somewhat new to me as I've never had to do any neck turning at all prior to this because I've never had tight chambers to deal with.

 

[sedancowboy]

There is no reason to do both inside reaming and outside turning. With outside turning the neck rides on a precision Carbide mandrel and the distance from the mandrel to the carbide cutter is fixed so the neck now has to be the same thickness all the way around. I usually turn my cases to .014 thickness and that cleans up most cases and works in most chambers. If I had a custom chamber that would not allow that thick of a neck then I would make a change. I use this formula Bullet Dia. + neck thickness+neck thickness = total dia of a case with bullet seated. Example .264+.014+.014= 292 so I would want a chamber with a neck dia of .296 and I would want a sizing die bushing of .289.

 

[Schnyd112]

Turning on the outside also allows you to cut into the shoulder just slightly to form a bit of a shelf at the neck shoulder junction. When you fire it, this forms on the inside and can help prevent donuts because the neck is thicker than the neck/shoulder junction. Inside reaming can remove donuts but they will always come back because you creat a 90 convex corner of brass that has nothing to keep it from following the bullet and flowing into th bottom of the neck.

If you inside neck ream, you are more limited by your die, or your drill. Outside neck turning you expand with a mandrel then turn the brass on the same sized mandrel, you are more limited by your skill. It takes some time to get the feel and the speed and everything right. I ruined some cases, then decided to practice on crappy brass, now I have it down pretty good. I can turn to .0145, .0140, .0135 and so on pretty consistently with the adjustment marks on my k&m tool.

This is easier to explain with a drawing, if my explanation doesn't make sense let me know.

 

[WildRose]

Turning on the outside also allows you to cut into the shoulder just slightly to form a bit of a shelf at the neck shoulder junction. When you fire it, this forms on the inside and can help prevent donuts because the neck is thicker than the neck/shoulder junction. Inside reaming can remove donuts but they will always come back because you creat a 90 convex corner of brass that has nothing to keep it from following the bullet and flowing into th bottom of the neck.

If you inside neck ream, you are more limited by your die, or your drill. Outside neck turning you expand with a mandrel then turn the brass on the same sized mandrel, you are more limited by your skill. It takes some time to get the feel and the speed and everything right. I ruined some cases, then decided to practice on crappy brass, now I have it down pretty good. I can turn to .0145, .0140, .0135 and so on pretty consistently with the adjustment marks on my k&m tool.

This is easier to explain with a drawing, if my explanation doesn't make sense let me know.

You're making sense but I keep returning to the fact that we work the brass from the outside thus pushing the eccentricities to the inside.

I've inspected thousands and thousands of rounds of new and X fired brass over the years and often see the thinning on the inside rather than the outside. With those cases if we're only milling the outside rather than the inside we will quickly reach a point where it's so thin in places it's no longer serviceable.

Remove it from the inside and there's far more material left for more firings. That at least seems to make the most sense to me.

I do appreciate all the help here but sometimes I just have to go ahead and put my hands on things and screw a few up before it all makes sense. HA!

 

[Wedgy]

I use the K&M turner but I much prefer the PMA holder as it centers and holds the case on the primer pocket and doesn't come loose as easy as the K&M chuck.

http://www.pmatool.com/caseholders-and-drivers-1/

 

[Clucknmoan]

You're making sense but I keep returning to the fact that we work the brass from the outside thus pushing the eccentricities to the inside.

This is why it makes more sense to me to expand out to tension and force those inconsistencies to the outside. I just buy madrells for .002 and .004 tension in each caliber.

 

[WildRose]

This is why it makes more sense to me to expand out to tension and force those inconsistencies to the outside. I just buy madrells for .002 and .004 tension in each caliber.

I get you but I don't see how you can put enough pressure on them from the inside to force those outward.

Nearly all of the damage to the brass done by friction and heat causing thin spots occurs on the inside.

When working down from the outside then it seems to me at least you are running out of material to work much quicker.

Maybe I'm just overthinking this. I'll have my gear in hopefully tomorrow or Monday and instead of thinking I can start doing which I'm much better at.

 

[WildRose]

I use the K&M turner but I much prefer the PMA holder as it centers and holds the case on the primer pocket and doesn't come loose as easy as the K&M chuck.

http://www.pmatool.com/caseholders-and-drivers-1/

I really like the look of those, thanks.

 

[Gord0]

With reaming, if your brass neck thickness varies to start, it will still vary after. A reamer will follow the hole. Outside turning on a mandrel will true the neck thickness up.

 

[BountyHunter]

You are not pushing anything to the inside IF you use the correct mandrel. There is no slop so everything is cut true. I do not think you understand that if you keep saying you are pushing to the inside. There is a reason every precision shooter uses neck turning. THE ONLY time reaming is used is it cut the majority of brass out after sizing cases down several calibers and then you resize, use the correct mandrel and neck turn for final. It does not get any simpler than that!