Neck turning case prep

[Ledd Slinger]

This is kind of the basis to my question.
If you're turning fire formed brass, wouldn't the inside neck diameter be a few thousandths larger than your turning mandrel, hence needing a turning mandrel of a larger diameter?
I know the turning mandrel is roughly .0005-.001 smaller than expander giving a good fit with clearance.
Or should I not worry about the extra clearance as the brass is riding the mandrel on top and held there by the cutter?
I'm using 21st century lathe setup.

You FL size then run the neck through the expander mandrel. The expander makes the brass fit the turning mandrel but also serves to straighten the inside of the neck and make it perfectly concentric with the turning mandrel. The brass is pressed between the cutter and turning mandrel as it’s being turned. That clearance will not change and thus cuts an even thickness down the entire neck. Get a neck wall thickness gauge to check if it worries you but you’ll be wasting your money if using a 21st Century neck turner because they are extremely precise cutting tools.

The Redding neck wall gauge can check thickness of the walls at any point fore and aft and is great for ensuring your cut thickness is correct for what you are trying to achieve. I will usually use a piece of cull brass to set up the turner and check my cut thickness and depth on the shoulder cut. But I quit using it for checking uniformity of cut thickness on the wall at different points once my 21st Century turners are set up because they always cut so perfectly every time.

 

[Bc'z]

You FL size then run the neck through the expander mandrel. The expander makes the brass fit the turning mandrel but also serves to straighten the inside of the neck and make it perfectly concentric with the turning mandrel. The brass is pressed between the cutter and turning mandrel as it’s being turned. That clearance will not change and thus cuts an even thickness down the entire neck. Get a neck wall thickness gauge to check if it worries you but you’ll be wasting your money if using a 21st Century neck turner because they are extremely precise cutting tools. The neck wall gauge can check thickness of the walls at any point fore and aft.

View attachment 1326857

Thats how I do it, I may have misunderstood @butchlambert when he said he was turning fired brass, wondering how FF brass would fit the turning mandrel.

 

[Ledd Slinger]

Thats how I do it, I may have misunderstood @butchlambert when he said he was turning fired brass, wondering how FF brass would fit the turning mandrel.

Perhaps his chamber is set up so that a fired piece of brass fits his turning mandrel but that’s not something I would recommend to anyone in general. Especially because once a straight neck designed reamer cuts a couple chambers it starts to create chambers with tapered necks whether you want that or not because the forward most cutting edges on the front of the reamer get worn more than the following edges. You might have a nice straight neck on the first one or two chambers cut with a new reamer but they will probably start to taper after that.

I have reamers with taper designed into the neck so I definitely wouldn’t turn a fired case even if it seemed to fit the turning mandrel. And if you don’t know your exact chamber design dimensions or how many cuts are on the reamer used on your rifle you definitely wouldn’t want to turn fired cases either. I recommend ensuring a neck is straightened and concentric by using an expander mandrel first.

 

[JSH]

I trim after FF, unless it causes a chambering issue or is grossly over length. I have never had a wildcat cartridge case FF and end up with a square case mouth.

If a case has to move much brass when fire forming, I would say annealing should be done to get a nice case. Even virgin brass can end up with some rounded shoulders.

 

[Ledd Slinger]

Best to fire brass first before neck turning. 2 firings on the brass is best but one firing will do.

With a tight neck chamber, i neck turn new brass just enough so a loaded round fits then shoot it and do a second turning after it’s Fireformed.

 

[butchlambert]

Thats how I do it, I may have misunderstood @butchlambert when he said he was turning fired brass, wondering how FF brass would fit the turning mandrel.

Check my post again. Fireforming with an unturned piece of brass in a chamber for turned necks leaves the ID of the neck only very little smaller than your expander. Your expander will have a much easier job and doesn't upset your brass like expanding first and turning.
Just fireform 1 piece of brass like I suggested and tell me your opinion. It is easier on your barrel that doing it with a bullet if you don't have a fire forming barrel.

 

[Bc'z]

Check my post again. Fireforming with an unturned piece of brass in a chamber for turned necks leaves the ID of the neck only very little smaller than your expander. Your expander will have a much easier job and doesn't upset your brass like expanding first and turning.
Just fireform 1 piece of brass like I suggested and tell me your opinion. It is easier on your barrel that doing it with a bullet if you don't have a fire forming barrel.

Now I'm understanding what you're saying.
I'm still new to turning maybe 400 pieces, but I catch on fairly quick.

 

[Bc'z]

I trim after FF, unless it causes a chambering issue or is grossly over length. I have never had a wildcat cartridge case FF and end up with a square case mouth.

If a case has to move much brass when fire forming, I would say annealing should be done to get a nice case. Even virgin brass can end up with some rounded shoulders.

I turned some new 308 for my brother before sizing down to 7mm, then it was blown out to 7-08ai. Fun project.

 

[Ccrider]

I can see fireforming first with a no turn neck. How are you guys fireforming before turning when the cartridge will not chamber like in a .268 neck Bra?

 

[Hiredgun81]

Perhaps his chamber is set up so that a fired piece of brass fits his turning mandrel but that’s not something I would recommend to anyone in general. Especially because once a straight neck designed reamer cuts a couple chambers it starts to create chambers with tapered necks whether you want that or not because the forward most cutting edges on the front of the reamer get worn more than the following edges. You might have a nice straight neck on the first one or two chambers cut with a new reamer but they will probably start to taper after that.

I have reamers with taper designed into the neck so I definitely wouldn’t turn a fired case even if it seemed to fit the turning mandrel. And if you don’t know your exact chamber design dimensions or how many cuts are on the reamer used on your rifle you definitely wouldn’t want to turn fired cases either. I recommend ensuring a neck is straightened and concentric by using an expander mandrel first.

I had never thought of this before, but often wondered why FF necks had a measurable taper. When the reamer print or cartridge drawings clearly showed a straight neck. Great explanation!

 

[butchlambert]

C

I can see fireforming first with a no turn neck. How are you guys fireforming before turning when the cartridge will not chamber like in a .268 neck Bra?

Cc, my 6BR Lapua measures .2675. It fits. Try one before making a decision.

 

[butchlambert]

Perhaps his chamber is set up so that a fired piece of brass fits his turning mandrel but that’s not something I would recommend to anyone in general. Especially because once a straight neck designed reamer cuts a couple chambers it starts to create chambers with tapered necks whether you want that or not because the forward most cutting edges on the front of the reamer get worn more than the following edges. You might have a nice straight neck on the first one or two chambers cut with a new reamer but they will probably start to taper after that.

I have reamers with taper designed into the neck so I definitely wouldn’t turn a fired case even if it seemed to fit the turning mandrel. And if you don’t know your exact chamber design dimensions or how many cuts are on the reamer used on your rifle you definitely wouldn’t want to turn fired cases either. I recommend ensuring a neck is straightened and concentric by using an expander mandrel first.

I fire form first without a bullet first to ensure I have a straight neck. A mandrel doesn't make a neck straight.
Try it before nixing the idea.

 

[Ccrider]

I fire form first without a bullet first to ensure I have a straight neck. A mandrel doesn't make a neck straight.
Try it before nixing the idea.

Will do.

 

[BORGY76]

I fire form first without a bullet first to ensure I have a straight neck. A mandrel doesn't make a neck straight.
Try it before nixing the idea.

FF without a bullet, can you give me some insight? Do you just plug the neck with( I guess I'm not sure what is usable)? Doesn't a pressed bullet create the pressure needed for the forming to occur? Sorry for the probably dumb questions.

 

[Dusty Stevens]

FF without a bullet, can you give me some insight? Do you just plug the neck with( I guess I'm not sure what is usable)? Doesn't a pressed bullet create the pressure needed for the forming to occur? Sorry for the probably dumb questions.

Fast burning pistol powder like bullseye and no filler except toilet paper or wax to keep the powder from spilling will fill the cases out just right

 

[BORGY76]

Fast burning pistol powder like bullseye and no filler except toilet paper or wax to keep the powder from spilling will fill the cases out just right

Gotchya, makes sense.

 

[Alex Wheeler]

I find carbide mandrels that fit very snug in new brass. Turn them straight out of the box, no sizing or expanding. You will need to use lube and keep the tool cool, but I can hold .0001" like this. You dont want the cutter too sharp either, a little push off helps consistency.

 

[Link]

How important is neck turning in the big picture of accuracy at short range ,say out to 400 shooting score not group? While were at it how about tension?

 

[AlNyhus]

Fast burning pistol powder like bullseye and no filler except toilet paper or wax to keep the powder from spilling will fill the cases out just right

Virgin Lapua 6BR cases right from the box ready to f-form to 30BR in the 1.520 length chamber. Winchester 231 powder, toilet paper and Play Doh. I like the blue Play Doh best . But I'll use whatever color that's on hand.

The result is perfectly round/straight case necks. The part of the shoulder that becomes the outer 'lump' when expanded manually isn't there. It's on the inside now and is thinner and longer than when it was on the outside. I remove it before outside turning.

Good shootin' -Al

 

[Link]

Nice to see AlNyhus on board, thanks.

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