Neck tension question

[Wildstreak]

My micrometer is not what I would call a quality, precision instrument. I do not have a ball micrometer but I do have a nice set of Mitutoyo calipers.

My question is, can I measure the thickness of my case neck using my calipers, factor in the bullet diameter to quantify my OD and accurately set my neck tension from that?

Such as the Peterson brass for my .280 has been no thinner than .015 so:

.015 + .015 + .284 = .314

Based on that I should be able to use a .312 neck bushing and achieve .002 neck tension.

Will this work?

 

[MagnumManiac]

My micrometer is not what I would call a quality, precision instrument. I do not have a ball micrometer but I do have a nice set of Mitutoyo calipers.

My question is, can I measure the thickness of my case neck using my calipers, factor in the bullet diameter to quantify my OD and accurately set my neck tension from that?

Such as the Peterson brass for my .280 has been no thinner than .015 so:

.015 + .015 + .284 = .314

Based on that I should be able to use a .312 neck bushing and achieve .002 neck tension.

Will this work?

You need to take into consideration that all brass springs back, this may or may not matter to you, but I find .0005" is normal springback across the board.

Cheers.

 

[Coyote Shadow Tracker]

Your calculation is correct.
You should use a "Ball Micrometer" to get a correct measurement.
You can also measure a loaded cartridge with your caliper at the neck and get the total and then - 0.002.

 

[Coyote Shadow Tracker]

If you are going to use a "Sizing Die with Bushings" you really should be "Turning" the Necks to get a consistent wall thickness. Then you can use the correct Bushing for the neck tension you want.

 

[243winxb]

Seat a bullet in an empty brass. Measure outside neck diameter. Subtract .003" This is your bushing size.

Do use an expander for unturned brass. Lube inside of neck. Look for light expander drag, as expander comes out of the necks, of each.

 

[cdherman]

Seat a bullet in an empty brass. Measure outside neck diameter. Subtract .003" This is your bushing size.

Do use an expander for unturned brass. Lube inside of neck. Look for light expander drag, as expander comes out of the necks, of each.

Lots of folks use .002 under measured OD on loaded cartridge. I personally hate to over work the brass. Even though I anneal every so often. (really depends on the circumstances, cartridge, number of rounds in the lot etc)

Overly tight neck *might* actually be more accurate sometimes. So the recommendations for a tighter neck should not be dismissed immediately. Not that .003 referenced above should be any tighter than .002, given the expander ball is the same, BUT brass springs back and the more you work it, the springier it gets.

I hate using an expander ball. Means lubing the neck, and then how do I clean that off? I prefer a mandrel and graphite, which has no impact on propellant or primers.

When measuring the OD of a loaded round (it can be a dummy of course, with no powder) make sure to rotate the cartridge a couple times and measure from a couple different points. And best is several different cartridges. A good Mitutoyo will show variation on all the stuff, just little enough that you are happy......

You will find variation. Even in the best stuff. Take an average. Want perfect? Turn the necks. Personally not willing....

I have a ball mic too. Results of both methods correlate.

 

[dfanonymous]

You need to take into consideration that all brass springs back, this may or may not matter to you, but I find .0005" is normal springback across the board.

Cheers.

You're not going to give him a 3 post lecture on how it's "interference" and not neck tension?

 

[Tiny Tim]

If you don't have a ball mic, a better way to know what bushing to use/ obtain, is to seat a bullet and measure the loaded neck diameter.

Mist of us have a way of removing a bullet without damaging it so components can be reused.

Aside from that, I like to expand the necks as a last step so if there is any residual stress in the brass that may "release" over time, it increases interference fit rather than decreasing it.

 

[PNWdude67]

My micrometer is not what I would call a quality, precision instrument. I do not have a ball micrometer but I do have a nice set of Mitutoyo calipers.

My question is, can I measure the thickness of my case neck using my calipers, factor in the bullet diameter to quantify my OD and accurately set my neck tension from that?

Such as the Peterson brass for my .280 has been no thinner than .015 so:

.015 + .015 + .284 = .314

Based on that I should be able to use a .312 neck bushing and achieve .002 neck tension.

Will this work?

It's a place to start but maybe not the oat consistent way… or maybe it's more correct to say your solving half the problem. You are reducing OD with the bushing from the expanded firesd form. What should be done next to "set" neck tension is the expander or turning .284 mandrel to more consistently establish the "neck tension" . There's is a .001 difference between the two mandrels. Before all this anneal, I do it every firing which eliminates separating batches. As long as you do it all consistently doesn't matter which mandrel or how often you anneal. The more consistent the prep the more visiting results down range will be.

 

[MagnumManiac]

You're not going to give him a 3 post lecture on how it's "interference" and not neck tension?

Why would I bother, you just told him…

 

[BigMeech556]

Me personally I say find what neck tension or "interference" you want and get an expanded mandrel in that size then go .001 less with your bushing so you are setting your final with the expander mandrel. Also why I love the sac modular die because it has it in the die so it's 1 pull to do it all

 

[BigMeech556]

Me personally I say find what neck tension or "interference" you want and get an expanded mandrel in that size then go .001 less with your bushing so you are setting your final with the expander mandrel. Also why I love the sac modular die because it has it in the die so it's 1 pull to do it all

 

[osok-1k]

So many thoughts and processes, my first question is application. If you're loading for a hunting rifle and your loads without all of the work shoot in the MOA range, you don't need to be concerned with with prepping cases to the 'nth degree because you aren't going to be able to shoot that accurately anyway unless you're very well supported in your shooting position. If you're shooting competitions where the tiniest variations matter, then by all means go through the processes to create the most consistent loads you can. But you would not likely be using a 280 for competition. My suggestion is to use graphite on your neck with a carbide expander ball if you can find one (Lee makes a carbide sizing die with carbide expander, never used one but it could be interesting). I also like Wilson's inside neck turning tools which allow you have a consistent surface on the inside of the neck and remove the donut if the is one. Some articles on Accurate shooter state that some of the best shooters in F Class and other disciplines don't do much to the case. I'm a little too anal for that but you can spend an amazing amount of time, effort and expense for very little gain over carefully loaded rounds or even some good factory match ammo which has no appreciable case prep other than possibly weighing. I shot a .270 group at 200 yards in my LE sniper school using Federal Gold Match factory ammo.

With all of that, I will admit that there is a degree of confidence and satisfaction in shooting carefully prepped and loaded ammo regardless of the application and when you're looking through the scope at your target, be it a critter, paper or other, one needs to be confident in the shot before you press the trigger.

 

[7stw]

Fortunately, at this time, I only have one rifle that I need to turn necks on, which is my 22br. This rifle, has a .250 neck diameter, which boils down to me needing to remove .001-.0015 or so. I have a .246, and .245 bushing. Depending on what BRAND of brass I use, and I have two. ( Peterson, and Norma), I find that sometimes I can use the .246 bushing, on one brand, and use the 245 on the other. So, given the necks are turned to the same wall thickness, the amount of springboard can vary enough to make the need for another bushing size. This in turn, effects desired Neck tension.
One thing I've learned through this turning process, and learning curve, is how much , wall thickness irregularity that I find , in even the "Premium" brass. My end thickness is typically .00135 or so. That said, my cutter sometimes skips, while turning, and sometimes, it gives a full cut, even with same lot of brass. Point is, turning does ensure uniform neck wall thickness, which helps concentricity. Hope this helps, and not to confuse. All the best to all.