Determining neck bushing size for die

[elktaker]

I had another thread but started this one just on how to determine neck bushing size.

My chambers neck is suppose to be:

.322" at neck

I am going to use an inside reamer:

It measures .287"

I plan to turn down my necks to .012" meaning that i would need .306 neck bushing for .002" of tension (.284 + .12(2) - .002) Correct? Hopefully, bc I order that one!

Do i need another bushing to do the inside reaming or will firing the case in my chamber and using the .287" skim the inside of the neck after its been fired?

I am not sure how the rebound of the neck will affect the inside dimension after firing.

.322"-.287" / 2 equals neck thickness of .0175" to fill chamber and have inside diameter of .287".

Do I need another bushing to bring the neck down to have an inside diameter of .287"? Math would be:

.287"(reamer)+ 2 x .012 (neck thickness) = .311" outer diameter.

I would take fired brass that has been neck turned to .012" before firing and run it through a .311 neck bushing. Then I would ream the inside with .287 reamer.


Is this correct or is there an easier way? My necks are only .0145 to .015" thick so using a neck of .0175" from the start will not work. This is from fireforming norma 300 wsm.

 

[Mikecr]

You're all fuddled up..
The reaming is a bad idea, drop all that.

If your chamber neck is .322" then why would you reduce thickness to put loaded necks at .308?
You intend 14thou neck clearance?

Also, don't forget dynamics in brass. There is spring back from each yielding direction. And don't forget pre-expansion as part of your neck sizing.
Bullets are the very worst of expanders.

Tell us what you want & we'll tell you how to get it.

 

[elktaker]

I am trying to elimate donuts and had good brass life.

Currently I have coming

Redding s bushing full length die (I am planning to use so whatever I do well utilize this)
I got a 306 bushing which looks like I will be get a different one which is fine.
50 pcs of Norma 300 wsm brass to ff cream of wheat style to 7mm wsm
A Forster had neck turner
A reamer to fit my trimmer in 284 (actually 287)

Already have a redding vld seater and fl die.

Bullets must be loaded pass shoulder to fit in mag and barrels throat.

What should my process be and what else do need? Reamer seems to be the only way to 100% eliminate a donut forming.

 

[Mikecr]

[CYBER SLAP] Look at the mess you're getting yourself into!

Your chamber neck is .322
Your neck brass is .145 thick, X2 is .029, over .284 bullets = .313
.322-.313 = .009 clearance already(excessive)
Don't ream or turn further.

Not sure why you're not using 7WSM brass.
Sizing down 300 to 7mm will thicken necks but you will still have plenty of clearance.

You intend to seat bullet bearing through neck-shoulder junction?
That's more bad planning..[CYBER SLAP]
But you can do this by partial neck sizing with bushings followed by expanding donut area outward, every time, away from seated bearing. You should have all the clearance in the world to provide for this. I recommend Sinclair's expander die setup.

That's it;
Partial bushing neck sizing including normal expansion.
With huge clearance, plan to anneal every time, or the necks won't survive long, much less give you consistent tension.
For your case I would start with a .311 bushing for unturned/unreamed necks followed by expansion.
Again with huge clearance, bushings over size at >5thou change, so .311 is only a beginning guess.
Down load first fire forming shots (to near min load). Develop with formed brass.

 

[elktaker]

Okay here are some results.

Used a .311 bushing to size approximately 85-90% of the neck and outside neck turned all my old brass necks to .0145 some were a little thicker but most were close to .0145.
I bumped the shoulders back .001 or .002 depending on previous load/brass to fit chamber.

I scored a few pounds of magpro so decide to switch away from Norma MRP.

First I shot 2 sighters then shoot 4 shoot groups with 2 minutes between each group. I had enough brass to load the following:

Group 1 64.9gr
.969 MOA
offset .095"L and .741"high

Group 2 65.4
1.1 MOA
offset .89L and .83 high

Group 3 65.9
.596 MOA
offset 1.075L and .44 high

Group 4 66.4
1.742 MOA
offset .019L and .263 high

Group 5 66.9
1.096 MOA
offset .749L and .569 high



Groups 2 3 and 5 have relatively close distance from point of aims. I believe my next step is to load 5 shot groups of:

65.5
65.7
65.9
66.1

To locate where the group the point of aim shifts between Group 3 and 4?

Groups were shot off of a new bald eagle front rest and rear bag of bench. Slight wind to the right 7 to 10 mph and 80 degrees. I typical like shooting groups that vary by .3 gr but brass dictated .5gr.