neck tension

[Bart B.]

Some graphite contains some abrasives, be careful what you use.

Dissimilar metal electrolysis can bond some types together. Cartridge brass and bullet copper are close enough on the scale that they seldom bond together.

Military rifle ammo has used an asphalt type sealant between bullet and case neck for decades. Competitive shooters often used the Lyman 310 tong nutcracker tool to seat match bullets a few thousandths deeper breaking the seal producing more uniform bullet extraction force, muzzle velocity and less vertical shot stringing.

[BJung]

So hounddawg, for long-term storage of reloaded ammo, you'd suggest rolling the bullet on a graphite pad. Would you wipe the inside of the case and let it dry with a solvent of some type?

[BJung]

how do you find the right graphite that's not abrasive?

[Bart B.]

Ask the maker. Some types list abrasives in their label.

True graphite is not abrasive, it is a lubricant. It is very messy though. Be certain that you have graphite rod, not carbon rod, which is abrasive.

[hounddawg]

Reread the chapter by Litz and starting to wonder exactly how much of the effect of .001 neck tension would make. It might be worthwhile to load up ten with .002, .003, and .004 and shoot them round robin while recording on my target cam. Maybe three groups of ten each

[Bart B.]

Originally Posted by hounddawg

Reread the chapter by Litz and starting to wonder exactly how much of the effect of .001 neck tension would make.

It depends on how hard or soft the brass is. It'll be less with soft brass.

It's easy for me to pull a broomstick out of your hand if you're gripping it lightly. The harder you grip it, the more pulling force I have to use to move it.

How would you measure your hand tension on the broomstick in fractions of an inch?

[hounddawg]

contrary to popular belief hardness and softness would have minimal to no effect. Possibly a very slight effect due to surface friction but definitely less than a bit of lube in the neck would have. Ask any blademaker how hard the steel is in a old auto leaf spring. Brass used in clock and other springs is extremely hard with a Rockwell B rating of 90. Fully annealed brass has a rating of 64.

What I have noticed though is annealing does affect the yield point where brass goes from the elastic to the plastic phase when being deformed. Seat .264 bullet in a case with .261 neck ID and pull it. In my (informal) tests the freshly annealed brass would spring back to .262, the work hardened back to .0263. That tells me that the annealed has a higher yield point than the work hardened allowing more stretch before going to the plastic phase. I am doing a informal 40 round "flyer test" when the wind stops making white caps on the retention pond, just to see if it make a darn on target. The Annealeeze may get brought back from retirement

[hounddawg]

How would you measure your hand tension on the broomstick in fractions of an inch?

apples to oranges comparison

all materials have a fixed linear elasticity. Imagine cutting strrip of brass and stretching the strip linearly. It requires X amount of force to do so. In a case neck the same thing is happening, as you force a bullet into the neck the brass stretches. That force needed to stretch that brass is a fixed number known as the Elastic (Young's, Tensile) Modulus. That is a fixed number and is determined by the relationship of protons and electrons in the alloy. Think of milions little magnets attracting and repelling each other



Annealing will not affect that number but it will affect the stress strain curve where the metal goes from the elastic phase where it "snaps" back and the plastic phase. You can demonstrate this at home by bending a piece of metal in a vise. You will find that to make a 90 degree bend you have to bend the metal past 90 degrees. When you insert a bullet into a case neck, you are stretching that brass out a few thousandths and ideally when you pull the bullet the case will spring back same measurement as when you seated the bullet. From the experiments I have done so far though they have not. The work harded brass exhibited less springback than the annealed. I don't have any factory fresh .260 brass to try it with. I do have some Starline and Hornady 6.5 Grendel though and will seat some bullets pull them and measure later.

Anyone can play with this at home with nothing more than your calipers and making some dummy rounds. Try it factory fresh brass and old work hardened brass. If you have a bushing sizer try different bushings. Interesting stuff for me anyways

edit- The ideal is to have the necks have to have equal thickness and to be equally stretched, that will apply a equal amount of surface friction to hold the bullet. Oddly enough or perhaps not I found that by varying the surface friction with lubes I found almost no variation if muzzle velocity once a certain amount of tension was applied. That led me to believe that once a certain point is reached the pressure from the burning gas will pop the bullet out and further tension had no effect on muzzle velocity. That could also explain why in Litz's experiments there was minimal difference between .001 and .003 neck difference as far as muzzle velocity was concerned. However in the smaller cartridges that unseating pressure could have been reached slower due to the powder used in those cartridges leading to larger differences in ES and SD in the smaller volume cartridges.

Be that as it may I am not under the illusion that I have the accuracy of a machine rest shooting in a absolute vacuum in a test tunnel. I am only concerned as how variations in loading practices affect my shooting in the real world and whether any changes can be seen through the noise of own techniques and the effect of environmental factors during matches

end edit

[Unclenick]

@UncleNick - that's great but in the real world most of us do not have the training or equipment to determine real neck tension. For those who want to then clean the brass to bare metal, measure the thickness to .0001 and here is the math

https://study.com/academy/lesson/ela...surements.html

It's not too often I get to say someone else is overcomplicating something. You don't need to determine elastic modulus for brass for yourself; you just look it up on matweb.com if you need it. It one piece of the puzzle you need to make the hoop stress and strain calculations, though there are online calculators that will do it for you.

I’m not expecting anybody to do that. I only pointed out, and as SAAMI defines it, interference fit is not actual neck tension. The reason to know they are different is that moving from, say, 0.001 to 0.002 interference fit has a different effect on bullet pull for different calibers. So you are correct that you have to do some shooting to find what you actually want to know.

The main source of the problem is that you only get to expand a neck just so far before you pass the yield of the brass and it starts to deform permanently and no longer applies a proportional increase in tension with increasing interference fit. Beyond about 0.0015” you don’t really get very substantial increases in pull, even when the brass is hard enough not to yield too easily. So people seeing improvement from more interference fit than about 0.0015” are seeing something else going on, I think, like better bullet alignment or some other secondary effect from doing the job.

This article is pretty good, and you can look at the graph and see for yourself what the different calibers are doing.

Regarding graphite, the stuff used to make EDM electrodes and other artificial solid shapes all have a binder in them. It is the binder that is abrasive. Pure graphite or naturally occurring solid graphite don’t have that and won’t abrade anything.

[hounddawg]

you can call it a interference fit if you want. That's just semantics. Most shooters call it neck tension and that is the way I and every shooter I know communicates it.

If you really want to get technical it is surface friction. You have to take into account the contaminates on the surface of the bullet or brass. From what I have seen it is only relevant to a certain point anyway and then only on certain cartridges. Apparently according to Litz's research .001 is as good as .003 with .308 Win. With the 223 and .243 he found .003 was optimum or did he?

Thanks to the OP of the thread the discussion got me to thinking about if I was pushing my brass through the elastic phase of deformation reaching the yield point and getting into the plastic phase when seating a bullet. I found out I was. Example - I deform (stretch) the inner diameter of the neck .004 seating a bullet. Upon pulling the bullet the diameter is only smaller than the OD of the bullet I just pulled. Now did I have .001 .004 interference fit ? The annealed were .002 smaller when the bullet was pulled, was the interference fit .002? Maybe this is a argument for annealing. For me it is all dependent on how the groups print and number of random unexplained flyers


When the wind drops out of the double digits here Sunday or Monday I will shoot a couple of 20 round groups at 600 yards with annealed and non annealed just to see the grouping numbers. Could be that I might change my views on annealing once again, I saw no benefit from annealing with my previous testing but I would not mind finding out there is as long as a sufficient amount of actual shots fired on target convince me otherwise

edit - just looked up the SAAMI definition - https://saami.org/glossary/neck-tension/

underlining by me

The circumferential stress that the case neck exerts on the seated bullet, as a result of the interference fit provided by the case neck inside diameter and the bullet outside diameter.

several other factors come into play with neck tension other than the nominal interference fit. The condition of the surface areas in contact, rough, polished, bare metal, lubricants, thickness of the neck metal, and length of the shank in contact with the neck wall being the major players. But if Joe down at the range asks me how much neck tension and I say .003 he knows I am using a bushing that gives me a inside nominal .003 smaller than the bullet I am using

/edit

[Unclenick]

you can call it a interference fit if you want. That's just semantics.

Well, it would certainly be semantics if the terms meant the same physical thing, but you can tell by the units they don't, so I'm not sure whether it can be laid to semantics or not. Maybe so, in the long term, as misused terms often become common over time. As you note, SAAMI hasn't made the jump yet.

The problem with the reassignment of technical terms is always the potential for confusion. We had a hydraulic technician on the board once who couldn't discern pressure from force because the industry lingo referred to hydraulic line ratings as being in "pounds." It is actually in pounds per square inch, of course, but they are in the habit of dropping the last three words as an abbreviation, and this fellow took it literally. It caused him to make some very odd ballistic calculations because he couldn't see getting pounds force by dividing pressure by area. If the pressure was 60,000 psi, he thought it applied 60,000 pounds of force to any amount of area. I had a heck of an argument going with him because he wouldn't believe it and kept posting wrong numbers.

At issue here is that interference fit has units in inches while tension is in psi, and the one can't be converted to the other. So the inteference fit is, as SAAMI says, more literally a measure of what you use to cause hoop tensile stress (tension) but isn't the tension itself. You could certainly say you were setting the tension with it.

Anyway, your experience with pulled brass matches what Ive always seen with resizing and expanding necks, which is that they only spring back about 0.001" or so (varies with hardness and caliber), showing the elastic limit is about that much. After that, you get less increase in force from each additional thousandth of stretch. Not zero, just a lot less, as you are then past the knee of the curve.

Here's stress v strain a curve from a government report.

[hounddawg]

a good bar bet is betting someone they could not push a door open if there was a 1 psi of pressure on the other side. Answer of course is no, a standard door measuring 36 x 80 would have 2880 pounds of force pushing against it. 1 pound for every square inch of surface area. Any hydraulic tech will never take that bet

Same thing applies to the neck tension on a bullet. The more surface area of the neck contacting the bullet , the more force being applied. So deeper seating means more force. The thicker the neck brass the more force. Friction between the bullet and the neck will also affect the breakaway pressure. The less friction the lower the force needed to get that bullet moving

My current thought is you need a certain amount of force to build before the bullet starts to move but after that point increasing that number has little to no effect on accuracy or velocity consistency. Just a gut feeling from doing a lot of reading and thinking.

And as always the two main factors regarding accuracy are the shooter and the environment

[Bart B.]

Originally Posted by hounddawg

as always the two main factors regarding accuracy are the shooter and the environment

That was the reasoning of the British Commonwealth Rifle Association starting over a century ago. All competitors were issued an SMLE rifle and the same lot of 303 ammo. The competitors who were the best marksmen would shoot the best scores by their beliefs that all rifles were equally accurate with all lots of ammo

[hounddawg]

That was the reasoning of the British Commonwealth Rifle Association starting over a century ago. All competitors were issued an SMLE rifle and the same lot of 303 ammo. The competitors who were the best marksmen would shoot the best scores by their beliefs that all rifles were equally accurate with all lots of ammo

not what I meant at at all, but yes if all things are equal the superior markman will win out. However good equipment and ammo does count for something. It will just take you so far

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