Questions regarding the forming of 30 BR cases.

[BWS]

Hello everyone. I am a new member from Oz and have some questions re 30 BR brass forming from 6BR. I am new to neck turning and case forming.

I have a 30 Br barrel on order so I got some 6Br cases, a Sinclair Neck turning tool, Expander die and a bunch of stainless expander and turning mandrels. I also purchased a Wilson neck reamer to use with my trimmer.

I have expanded 4 case necks and they have donuts on the outside of the case neck. When I tried to insert the turning mandrel it only went into the case neck as far as the donut. So I went to ream the inside of the case neck with the Wilson tool and - nope it only works on fired cases.

The mandrels all work fine with standard cases that have not been necked up.

How do I remove that inside donut ? to allow me to turn the necks ?

I read recently on this site ( I think ) that the donut should be removed from the outside of the neck before turning. Is this the correct method?

What sort of tolerance is acceptable when trimming cases prior to turning? +/- 0.001?

Thanks

Simon

 

[Toby Bradshaw]

It's critical that the expander and turning mandrels are matched so that the expanded case neck has the proper fit on the turning mandrel. Typically this means that both mandrels come from the same supplier.

The donut is removed from the outside when the neck is turned, by turning slightly into the shoulder, like this:



I don't trim cases to length before neck turning -- I judge the length of the cut by how it looks, not by hitting a firm stop.

 

[BWS]

It's critical that the expander and turning mandrels are matched so that the expanded case neck has the proper fit on the turning mandrel. Typically this means that both mandrels come from the same supplier.

The donut is removed from the outside when the neck is turned, by turning slightly into the shoulder, like this:

View attachment 1052763

I don't trim cases to length before neck turning -- I judge the length of the cut by how it looks, not by hitting a firm stop.

Thanks Toby that photo is really clear and helps with how much to turn into the shoulder.
My expander and turning mandrels are all Sinclair and work fine with standard cases.
The problem I am having is not being able to insert the Turning Mandrel far enough into the case neck to be able to turn it.
This is only on the 6BR cases I have necked up to 30 cal. I tried necking up to 7mm first and then to 30 cal but no change.
It will only go in about as far as the donut that is visible on the outside of the neck.
I went searching for a turning mandrel from Sinclairs that had a cutter built in but wasn't able to find one.

How do you get around this issue? is this only me because I have found no reference to cleaning the inside of the neck anywhere?
Plenty of references to the donut on the outside.

Cheers

Simon

 

[Toby Bradshaw]

The problem I am having is not being able to insert the Turning Mandrel far enough into the case neck to be able to turn it.

There should never be a need to inside-ream a donut in a 30BR.

Run the case into the expander mandrel a couple of times, making sure that the entire neck/shoulder junction is on the full-diameter part of the mandrel. Then lube the turning mandrel/arbor well (I use 0W-20 motor oil, but any thin consistency lube will work) and push/twist the case onto the mandrel/arbor with as much force as required to get it past the donut.

If you're having this much trouble, you might verify the diameters of the expanding and turning mandrels with a micrometer that measures to 0.0001". Your expander mandrel should be approximately 0.001" larger than the turning mandrel/arbor, to allow for springback of the brass while still getting a snug fit on the turning mandrel/arbor.

 

[BWS]

There should never be a need to inside-ream a donut in a 30BR.

Run the case into the expander mandrel a couple of times, making sure that the entire neck/shoulder junction is on the full-diameter part of the mandrel. Then lube the turning mandrel/arbor well (I use 0W-20 motor oil, but any thin consistency lube will work) and push/twist the case onto the mandrel/arbor with as much force as required to get it past the donut.

If you're having this much trouble, you might verify the diameters of the expanding and turning mandrels with a micrometer that measures to 0.0001". Your expander mandrel should be approximately 0.001" larger than the turning mandrel/arbor, to allow for springback of the brass while still getting a snug fit on the turning mandrel/arbor.

 

[BWS]

I have run the case into the expander die dozens of times and get a nice fit until the front of the Turning mandrel hits whatever is stopping it. It doesn't just get tight, it stops dead.
This has happened in 5 out of 5 cases.
If i fit the Turning mandrel into the die then the weight of the press handle is enough to push past that point but no way can I push it on by hand. I can't feel or see anything inside the neck.

I measured the expander to be 0.3070" and the Turner to be 0.30575" So 0.00125" difference.
You can see on the photo the lines in the lube where it goes to. Seems to align with the outside donut.
What expander tools do most people use? Are these the wrong type for necking up brass?

Cheers
Simon

 

[Mega]

It sounds like your expander mandrel is not going all the way into the case with the main section of the shaft. I'm not familiar with the Sinclair gear, only use K&M where the die is two parts and has a window where you can see the top of a case neck to set the die height.

If done properly there is no way you should have a donut on the inside of the neck, the mandrel should push everything to the outside.

I also would not be playing with trimming cases to length until they have been fired at least once with a full charge weight.

 

[BWS]

Looks like the expander is not making it through the neck area of the case as you suggest.

The short case is the issue.
What is the diameter of the K&M expander? Might have to get one.

 

[Mega]

Where in Oz are you located..?? I'm in the Bathurst, NSW area. Just thinking if there is a way I can help you without too much expense.

Using Mitutoyo Calipres, the main stem diameter on my expander is 0.3080" and my mandrel is 0.3065". If that is a photo of your expander then mine is a lot different, longer. The K&M is a single pass from 6mm to 30cal and has a stop also to set the depth. I wouldn't know if the K&M gear will fit the Sinclair but as already mentioned you must use the set from the same maker. The only problem I ever had doing a few hundred 30BR cases was a few splitting necks in the process but I did discover that they may have had a fault already as I have some 6mmBR cases that have a crack/crease in the neck area.

If you would like to have a yarn on the phone I am quite happy to give you a ring and perhaps compare/advise a bit further.

 

[Toby Bradshaw]

It sounds like your expander mandrel is not going all the way into the case with the main section of the shaft.

This.

Edit: Here's the 21st Century expander setup, showing how the neck of even a short BR case can be driven to the full diameter of the expander mandrel.

 

[pat fulghum]

See my first post on this at this thread.
http://forum.accurateshooter.com/threads/initial-neck-turning-284-doughnut-causing-wobble.3943778/

What I have started doing is turn BEFORE expanding and the necks turned out much better.
This was on 284 brass, don't know about 30BR.

- pat

 

[BWS]

Right that looks like the go. Ordered one and a couple of carbide mandrels which seem to compatible with the Sinclair neck turner so that's a bonus.

Cheers Toby

 

[BWS]

Thanks Pat

That was an interesting read. Looks like one way to approach this process. It will not however fix the length of my expander mandrel so I will have
to sort that issue first.

Cheers

 

[BWS]

Where in Oz are you located..?? I'm in the Bathurst, NSW area. Just thinking if there is a way I can help you without too much expense.

Using Mitutoyo Calipres, the main stem diameter on my expander is 0.3080" and my mandrel is 0.3065". If that is a photo of your expander then mine is a lot different, longer. The K&M is a single pass from 6mm to 30cal and has a stop also to set the depth. I wouldn't know if the K&M gear will fit the Sinclair but as already mentioned you must use the set from the same maker. The only problem I ever had doing a few hundred 30BR cases was a few splitting necks in the process but I did discover that they may have had a fault already as I have some 6mmBR cases that have a crack/crease in the neck area.

If you would like to have a yarn on the phone I am quite happy to give you a ring and perhaps compare/advise a bit further.

Thanks Mega

The K&M expander is 0.001" larger than the expander for the Sinclair turner so it probably won't be compatible with the gear I already have.