Neck turning question

[alphapygmy]

I want to try and neck turn a batch of brass for my 260AI. I typically full length size, trim for length, then expand before turning. The issue I have is that all I have for sizing dies for my 260AI are a Redding bushing die and a lee collet neck die. Do I need to go spend a bunch more for a full length sizer to do it right or is there a way around this? I lean towards just getting the FL die to do it right.......

 

[Lapua40X]

I'm confused. If you "typically full length size" you must already have a FL die. If you're turning necks you don't need to use a FL die. You just need to make the corrections you want in the neck size. I neck size with the Redding bushing die, run the mandrel through the neck to round it out, turn the necks.

 

[SS427]

Take the bushing out and use the FL die as a bump die to set the shoulder at a uniform length. (Assuming it isn't a neck die.) Then run the expander mandrel through the necks to uniform the entire neck. Trim to length and then turn.

Maybe I am missing something.

 

[alphapygmy]

I meant I typically FL size before turning on my other calibers, like 308 or 260. This is my first oddball cartridge where dies are quite a bit more spendy and harder to get. I figured I shouldn't use a bushing die before turning because they don't size the bottom of the neck and it would make an thinner neck at the bottom. I made a pic of what I think neck turning a bushing die sized brass would do because it doesn't size all the way down to the shoulder.

 

[joshua43214]

Your fired brass should all be uniform length from base to shoulder, and concentric. This is especially true if you use a neck only die.

Just test fit the fired brass on the mandrel, if it fits turn away. If it is tight, use the expander mandrel then turn.

If it is loose, buy a match barrel

you can get a regular die, or you can just turn to the donut. In theory, the donut is not contacting the bullet so it does not matter if it is turned (theory, not sure I buy it). Look at how far down the bullet is seated, most BTHP bullets are designed to have the donut fit in the boat tail so that you don't have to neck ream.

 

[pdog]

alphapygmy,

Your assumptions are correct. You need a full length die to correctly neck turn your cases.

 

[dkhunt14]

Your fired brass should all be uniform length from base to shoulder, and concentric. This is especially true if you use a neck only die.

Just test fit the fired brass on the mandrel, if it fits turn away. If it is tight, use the expander mandrel then turn.

If it is loose, buy a match barrel

you can get a regular die, or you can just turn to the donut. In theory, the donut is not contacting the bullet so it does not matter if it is turned (theory, not sure I buy it). Look at how far down the bullet is seated, most BTHP bullets are designed to have the donut fit in the boat tail so that you don't have to neck ream.

If you have a tight necked gun and the bullet is in that area it does matter. The brass will be too thick and Pinch the bullet driving up pressure. I would prefer to full length size and then run a mandrel in. If the brass is new you can usually just run the expander in. Matt

 

[joshua43214]

Your fired brass should all be uniform length from base to shoulder, and concentric. This is especially true if you use a neck only die.

Just test fit the fired brass on the mandrel, if it fits turn away. If it is tight, use the expander mandrel then turn.

If it is loose, buy a match barrel

you can get a regular die, or you can just turn to the donut. In theory, the donut is not contacting the bullet so it does not matter if it is turned (theory, not sure I buy it). Look at how far down the bullet is seated, most BTHP bullets are designed to have the donut fit in the boat tail so that you don't have to neck ream.

If you have a tight necked gun and the bullet is in that area it does matter. The brass will be too thick and Pinch the bullet driving up pressure. I would prefer to full length size and then run a mandrel in. If the brass is new you can usually just run the expander in. Matt

I agree. Sorry I should have been more clear or provided a pic.

Found this image on Google and it illustrates what I meant

This is a flat base, but a BTHP will typically miss the donut as well. The OP's donut would be on the outside, but the point remains - in theory the donut does not matter if the bullet does not go there. Like I said, I am not sure I buy the theory.

If he had a tight neck, the brass would be too thick now, and the OP would be having pressure issues now.

Any way, there is a pretty good chance that the case neck comes out of the riffle ready for turning with out resizing and only using the expander. If the brass is too big, the brass will probably be short lived with out constant annealing anyway.
Another thought, if the case mouth is too big for the mandrel, the bushing die might bring it in enough with out the bushing to be trimmed. The die should have a slight taper just past the shoulder to help start the case into the bushing.

 

[mikecr]

alphapygmy, you're right about the partial neck sizing problem for turning.
Why don't you just turn new 260 brass right out of the box?
That is, no sizing other than a run over the turning system expander mandrel.
Fireform to AI later.

 

[LHSmith]

In theory, the donut is not contacting the bullet so it does not matter if it is turned (theory, not sure I buy it). Look at how far down the bullet is seated, most BTHP bullets are designed to have the donut fit in the boat tail so that you don't have to neck ream.

I don't think it's theory, but a proven practice. To my knowledge, no one has ever proved the donut to be detrimental to accuracy with bullets typically used in ShortRange BR ( i.e. bullets that are seated well clear of any donut).
There was a theory regarding Turbulence Point, in which case one who subscribes to that theory might argue the donut could upset or restrict the gas flow upon entering the case neck......but prove it on the target results.

 

[artbosco]

I meant I typically FL size before turning on my other calibers, like 308 or 260. This is my first oddball cartridge where dies are quite a bit more spendy and harder to get. I figured I shouldn't use a bushing die before turning because they don't size the bottom of the neck and it would make an thinner neck at the bottom. I made a pic of what I think neck turning a bushing die sized brass would do because it doesn't size all the way down to the shoulder.

You can use a bushing die! Take the bushing out before you size. Size. Neck up if required [depends on your cartridge]. Trim so all case necks are the same length when you turn into the neck/shoulder junction [That way it will be identical on each case]. Turn. Put the bushing back in when you're ready to F/L size before priming and dropping powder.

 

[alphapygmy]

I measuring a couple thou difference from base to datum line in new brass so I don't think they're consistent enough to turn right out of the box and I also don't know where the neck cut would end up if I trim then fire form. I'm using a Criterion barrel with .298 neck. The loaded brass is measuring .295 and they come out .297 after being fired so I have to do something to size the neck down to fit the turning mandrel. I may just do a set each way and run them at 600 yards and see what happens. 10 rounds each of unturned necks vs. FL sized and turned vs. with bushing die. With .004 neck clearance I shouldn't even have to turn but I want to at least experiment with any change in accuracy. Lapua brass is usually pretty dang good from the get go.

 

[noload]

3 of my 4 calibers are turn neck. After reviewing the end results against no turn and the work involved . I wished I bought no turn reamers. I admit theory dictates turned neck is more accurate, once the wind kicks in ( F-Class) you wouldn't notice the extra accuracy. If I only did BR, I would turn necks. I think neck wall thickness may vary .001", but if you size you cases within .001" TIR, plus .001" wall difference you are still an acceptable comparator runout of .002". So if you have .002" neck chamber clearance the neck thickness problem would almost go away. My best guess of accuracy difference between turn and no turn would be about .250" max at 300 yds. Thats about how I look at it.

 

[mikecr]

If it's Lapua 260 brass, you should expand and turn it right out of the box. This is what most people turning do.

If you have chamber end clearance already(any amount) you don't have to trim before fireforming(which will pull necks back on improvement). As far as turn onto shoulder, this you can eye. I never use a stop/particular turn trim length and have never seen it as difficult, or had any issue with it. Just be sure your cutter angle is a close match to shoulder angle.

 

[noload]

I also agree with eyeing the turn on the shoulder. No length trim needed.