Neck tension question

pwizl

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If I'm trimming the outside of the neck on my cases is it also necessary to size the neck with a bushing die to ensure correct neck tension? Or do these acheive two totally seperate goals. Thanks
 

ChrisGarrett

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Re: Neck tension question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pwizl</div><div class="ubbcode-body">If I'm trimming the outside of the neck on my cases is it also necessary to size the neck with a bushing die to ensure correct neck tension? Or do these acheive two totally seperate goals. Thanks </div></div>

No, you don't have to use a bushing die, as a standard die places neck tension on the bullet.

'Neck turning', in conjunction with 'inside neck reaming' are just ways to uniform neck wall thickness. This can help eliminate neck splits and it helps with more uniform neck tension, either from standard sizing dies, or from bushing dies.

Bushings allow you to alter that 'neck tension' in increments of .001", so they can be more precise and flexible, especially when using different brands of brass with varying neck wall thicknesses.

They are two different steps (concepts) but not totally unrelated.

Chris

ETA: spelling: 'alter'

 

TexIndian

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Re: Neck tension question

Two separate concepts. But I'd stay away from inside neck reaming as a general rule. Making thinner necks is rarely something you would want. Making neck walls that are uniform all the way around is the goal of turning.
 

pwizl

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Re: Neck tension question

[/quote]

No, you don't have to use a bushing die, as a standard die places neck tension on the bullet.

'Neck turning', in conjunction with 'inside neck reaming' are just ways to uniform neck wall thickness. This can help eliminate neck splits and it helps with more uniform neck tension, either from standard sizing dies, or from bushing dies.

Bushings allow you to alther that 'neck tension' in increments of .001", so they can be more precise and flexible, especially when using different brands of brass with varying neck wall thicknesses.

They are two different steps (concepts) but not totally unrelated.

Chris

[/quote]

Thanks for the reply Mr. Garrett. As far as measuring for the correct neck tension, do I use a fired case measure the outside diameter and subtract .002-.003 or do I measure a loaded case to take the measurement?
 

Unsichtbar

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Re: Neck tension question

Just a question what type of chamber does this rifle have?
 

Reefman69

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Re: Neck tension question

"Thanks for the reply Mr. Garrett. As far as measuring for the correct neck tension, do I use a fired case measure the outside diameter and subtract .002-.003 or do I measure a loaded case to take the measurement?"

to pwizl

what i do is take a case and measure the neck wall thickness, multiply x2, and add bullet diameter. for example hornady match brass is .013 in. of neck wall thickness. multiply x2 it gives you .026, add .308 and it gives you .334 in., subtract 2 thou., and it will give you 1 to 2 thou. neck tension, depending on spring back using a .332 bushing.
 

turbo54

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Re: Neck tension question

My method, which I'm more than happy with:

1. Seat a bullet in a sized cartridge.

2. Measure the OD of the neck.

3. Select a bushing .003" or .004" SMALLER than the measurement in step 2.

4. Finish size with a Sinclair "neck turning mandrel" after sizing the neck with the bushing.

5. Provides consistent and excellent .002" neck tension.
 

fokai_zach

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Re: Neck tension question

Neck tension = inner diameter of sized neck - outter diameter of neck with your complete ammo

Also are you shooting gas or bolt gun
 

pwizl

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Re: Neck tension question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fokai_zach</div><div class="ubbcode-body">Neck tension = inner diameter of sized neck - outter diameter of neck with your complete ammo

Also are you shooting gas or bolt gun</div></div>

Should have said that in the beginning, right now I'm shooting an AR-15 and I'm just getting started in reloading for accuracy. I'm going to be getting a bolt action .243 in the near future and I'm trying to get some techniques straight before I start reloading accurate ammo for that.
 

pwizl

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Re: Neck tension question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">My method, which I'm more than happy with:

1. Seat a bullet in a sized cartridge.

2. Measure the OD of the neck.

3. Select a bushing .003" or .004" SMALLER than the measurement in step 2.

4. Finish size with a Sinclair "neck turning mandrel" after sizing the neck with the bushing.

5. Provides consistent and excellent .002" neck tension.</div></div>

So if I understand all of this correctly, I would use the bushing to set the neck tension on the bullet and then trim the outside of the neck to fit the chamber correctly? So would I use a fired case to determine how much I need to trim the outside neck? Doesn't the neck bushing size reduce the outside diameter
enough for proper chamber clearance or does it depend on chamber size brass type and thickness of the brass at the neck. I'm so confused
 

Reefman69

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Re: Neck tension question

pwizl,
the whole point of using bushing type dies is so you may precisely control neck tension/size of the case neck due to changes in neck wall thickness. for example your lake city type brass will always be much thicker brass, thus reducing case capacity, hence why you should normally reduce loads roughly 1 to 2 grains, then work up. the other advantage is if you have a tight neck chamber, a standard factory die might not do the trick. you can have a custom die made by any major manufacturer, but will only properly size one specific type of brass the way you want it. when you turn your necks, your not sizing down the thickness of the neck for the purpose of making it thinner, you are simply making them more concentric. it may take off a half of a thou. in only some spots. this helps with reducing bullet runout, but you will need a concentricity guage to tell.
 

turbo54

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Re: Neck tension question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pwizl</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">My method, which I'm more than happy with:

1. Seat a bullet in a sized cartridge.

2. Measure the OD of the neck.

3. Select a bushing .003" or .004" SMALLER than the measurement in step 2.

4. Finish size with a Sinclair "neck turning mandrel" after sizing the neck with the bushing.

5. Provides consistent and excellent .002" neck tension.</div></div>

So if I understand all of this correctly, I would use the bushing to set the neck tension on the bullet and then trim the outside of the neck to fit the chamber correctly? So would I use a fired case to determine how much I need to trim the outside neck? Doesn't the neck bushing size reduce the outside diameter
enough for proper chamber clearance or does it depend on chamber size brass type and thickness of the brass at the neck. I'm so confused </div></div>

No.

With this method, you measure the neck OD of a few loaded cartridges... Say you come up with .336"... If you want a consistent .002" neck tension, you need a .334" bushing. That way, seating a bullet will cause the neck OD to grow .002" - meaing you've got .002" neck tension. Get it? If loaded OD is .336, then a sized neck of .334" + .002" neck tension = .336"

But! Sizing the outside of a tube is a lousy way to get a known, sweet inside dimension. This is because any variation in neck wall thickness will manifest itself as a variation in the circularity of ID. If you run the case up into a "perfect circle" neck sizing bushing, you'll end up with a less than "perfect" circle for your ID. A tool that works the INSIDE does a nice job of getting a known, sweet inside dimension (at the expense of your neck OD now being less than perfect)....so....for the above example, you would instead use a .332" bushing which would, if left as-is, provide .004" tension. Use a Sinclair mandrel that is a rod you drive into the neck, to now bump the neck UP .002" more.

This is essentially what a FLS die does with two key differences :

1. Decreases neck size (from fired size) the MINIMUM NECESSARY AMOUNT. FLS dies are notorious for necking the brass way small on the way into the die, to then drag an expander ball back through the neck on the way out of the die.

2. The case neck expansion to final ID size occurs with the case in compression, rather than tension as with a FLS die. Intuition and a solid understanding of engineering would suggest otherwise, but I can attest from first hand experience that doing the expanding on the ram upstroke produces better concentricity than doing it on the ram downstroke.

So to recap: a caseneck ready for bullet seating will measure smaller than one with a bullet in it. This difference IS neck tension. Its better to perform final sizing on the case ID, rather than OD, because the bullet touches tge ID, not OD. Thus, you choose a bushing that sizes the caseneck a little smaller than you need for bullet seating, then bump out the caseneck just a smidge with an expander mandrel that gets jammed down into the case.

By the way, its confusing, but the mandrel from sinclair that you want is called the "neck turning mandrel", not the "expander mandrel". The expander mandrel will produce only .001" neck tension.
 

armorpl8chikn

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Re: Neck tension question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rpat</div><div class="ubbcode-body">pwizl,
the whole point of using bushing type dies is so you may precisely control neck tension/size of the case neck due to changes in neck wall thickness. <span style="color: #CC0000">for example your lake city type brass will always be much thicker brass, thus reducing case capacity,</span> hence why you should normally reduce loads roughly 1 to 2 grains, then work up. the other advantage is if you have a tight neck chamber, a standard factory die might not do the trick. you can have a custom die made by any major manufacturer, but will only properly size one specific type of brass the way you want it. when you turn your necks, your not sizing down the thickness of the neck for the purpose of making it thinner, you are simply making them more concentric. it may take off a half of a thou. in only some spots. this helps with reducing bullet runout, but you will need a concentricity guage to tell. </div></div>

Wrong. What kind of research did you do on that piece of info before you advised someone?
.223 Rem Case Weight vs. Capacity
Case Manufacturer Case Weight* H20 Capacity**
Lake City 06 92.0 30.6
WCC99 95.5 30.5
Sellier & Belloit 92.3 30.5
Remington 92.3 30.4
PMC 93.5 30.4
Hirtenberger 93.7 30.4
Lake City 04 93.0 30.4
Federal 96.3 30.2
Hornady 93.9 30.1
IMG (Guatemalan) 95.4 30.1
Lapua (new lot) 93.4 30.1
Winchester 93.9 30.1
Olympic 97.4 30.0
Radway Arsenal 96.1 30.0
PMP 104.5 29.9
FNM 93-1 97.3 29.8
Lapua (old lot) 104.0 28.0
Information from Accurate Shooter website.
 

pwizl

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Re: Neck tension question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pwizl</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">My method, which I'm more than happy with:

1. Seat a bullet in a sized cartridge.

2. Measure the OD of the neck.

3. Select a bushing .003" or .004" SMALLER than the measurement in step 2.

4. Finish size with a Sinclair "neck turning mandrel" after sizing the neck with the bushing.

5. Provides consistent and excellent .002" neck tension.</div></div>

So if I understand all of this correctly, I would use the bushing to set the neck tension on the bullet and then trim the outside of the neck to fit the chamber correctly? So would I use a fired case to determine how much I need to trim the outside neck? Doesn't the neck bushing size reduce the outside diameter
enough for proper chamber clearance or does it depend on chamber size brass type and thickness of the brass at the neck. I'm so confused </div></div>

No.

With this method, you measure the neck OD of a few loaded cartridges... Say you come up with .336"... If you want a consistent .002" neck tension, you need a .334" bushing. That way, seating a bullet will cause the neck OD to grow .002" - meaing you've got .002" neck tension. Get it? If loaded OD is .336, then a sized neck of .334" + .002" neck tension = .336"

But! Sizing the outside of a tube is a lousy way to get a known, sweet inside dimension. This is because any variation in neck wall thickness will manifest itself as a variation in the circularity of ID. If you run the case up into a "perfect circle" neck sizing bushing, you'll end up with a less than "perfect" circle for your ID. A tool that works the INSIDE does a nice job of getting a known, sweet inside dimension (at the expense of your neck OD now being less than perfect)....so....for the above example, you would instead use a .332" bushing which would, if left as-is, provide .004" tension. <span style="color: #CC0000"> Use a Sinclair mandrel that is a rod you drive into the neck</span>, to now bump the neck UP .002" more.

This is essentially what a FLS die does with two key differences :

1. Decreases neck size (from fired size) the MINIMUM NECESSARY AMOUNT. FLS dies are notorious for necking the brass way small on the way into the die, to then drag an expander ball back through the neck on the way out of the die.

2. The case neck expansion to final ID size occurs with the case in compression, rather than tension as with a FLS die. Intuition and a solid understanding of engineering would suggest otherwise, but I can attest from first hand experience that doing the expanding on the ram upstroke produces better concentricity than doing it on the ram downstroke.

So to recap: a caseneck ready for bullet seating will measure smaller than one with a bullet in it. This difference IS neck tension. Its better to perform final sizing on the case ID, rather than OD, because the bullet touches tge ID, not OD. Thus, you choose a bushing that sizes the caseneck a little smaller than you need for bullet seating, then bump out the caseneck just a smidge with an expander mandrel that gets jammed down into the case.

By the way, its confusing, but the mandrel from sinclair that you want is called the "neck turning mandrel", not the "expander mandrel". The expander mandrel will produce only .001" neck tension. </div></div>

What's the best way to use the mandrel as far as getting in and out of the neck?
 

turbo54

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Re: Neck tension question

You buy the sinclair expander die, which threads into your press. You buy the mandrel(s) for your application(s), you thread the cap off the die, drop your mandrel in, replace the cap, set the depth of your die, put brass into shellholder in your press and run the brass up and onto the mandrel. Works like a charm.
 

JimGnitecki

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Re: Neck tension question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">[By the way, its confusing, but the mandrel from sinclair that you want is called the "neck turning mandrel", not the "expander mandrel". The expander mandrel will produce only .001" neck tension. </div></div>

If I understand this correctly, you end up with .002" neck tension. This is what Sinclair claims their NECK TURNING (versus "expander")mandrels provide.

But, isn't .002" a little "loose" for a semiauto gas gun? I'd personally feel more comfortable with .003", and perhaps .004" if the case neck walls vary in thickness at all.

But, Sinclair only offers neck turning mandrels that are .002" under bullet ID.

I did an exhaustive search to try to find a rifle caliber that has a .307" bullet, so I could get a mandrel that would give .003" neck tension with a 308 bullet, but none exists (closest is the 7.62 x 25 Tokarev metric PISTOL round), so no way to get a mandrel that is .305".

Yeah, a skilled machinest could turn or grind one down I suppose, without overheating and damaging it, but I certianly cannot.

Is .002" really reliably enough, given that even Lapua cases vary a bit in neck wall thickness? I don't have a ball-end caliper or micrometer, but my digital caliper measurements of the Lapua neck walls, using the caliper knife edges, gave me .0155" to .0165" range. Interestingly, all these Lapua cases came from ONE box, but were ALL INDIVIDUALLY EITHER .0155" or .0165", implying the box got laoded with cases from two different production machines, each of which was VERY consistent, but together produced this unfavorable mix.

So, with my current .336 bushing, and .308 Sierra 175g Matchkings,withOUT a mandrel, if you do the math you can see that I get EITHER .336 minus (.308 + 2 x .0155)= -.003" OR .336 minus (.308 + 2 x .0165) = .005".

What is my best option here?

Jim G
 

turbo54

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Re: Neck tension question

I haven't had any trouble with .002" neck tension with my AR10, and honestly, I don't believe it is possible to even achieve more than .002" neck tension with fresh Lapua brass or annealed brass. Here's why:

Brass in the annealed state is not a very ELASTIC material, so if you were to size the ID of your caseneck down to .300", and then seat a bullet, then pull the bullet, you'll find that caseneck ID is NOT .300 anymore. Rather, it's going to be .305 or .306", because the brass yielded as it was forced to stretch to accomodate the bullet.

Check for yourself. Take the decapping/expanding stem out of your FLS die, and run a piece of brass up into the die. Measure the neck OD. Seat a bullet (gonna be TIGHT) in the case and then measure the neck OD. Now pull the bullet out and measure neck OD again....its NOT going to be what it was (or even close) before seating the bullet - because the brass has yielded.

Now, as the brass gets worked/fired more and more without annealing, the brass gets harder. A fundamental rule of metalurgy is that when a metal gets harder, it gets stronger and it's yield strength increases. For that reason, the amount of "possible" neck tension is going to increase as the brass gets used more without annealing. How much? Don't know, haven't run the testing.

Lastly, if you want a smaller mandrel, why not chuck the mandrel in your drill and spin the mandrel in a piece of emory cloth or fine(ish) grit sandpaper. Say 320-440 grit or so? You should be able to peel .001 or .002 off in a couple minutes this way.
 

JimGnitecki

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Re: Neck tension question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">I haven't had any trouble with .002" neck tension with my AR10, and honestly, I don't believe it is possible to even achieve more than .002" neck tension with fresh Lapua brass or annealed brass. Here's why:

Brass in the annealed state is not a very ELASTIC material, so if you were to size the ID of your caseneck down to .300", and then seat a bullet, then pull the bullet, you'll find that caseneck ID is NOT .300 anymore. Rather, it's going to be .305 or .306", because the brass yielded as it was forced to stretch to accomodate the bullet.

Check for yourself. Take the decapping/expanding stem out of your FLS die, and run a piece of brass up into the die. Measure the neck OD. Seat a bullet (gonna be TIGHT) in the case and then measure the neck OD. Now pull the bullet out and measure neck OD again....its NOT going to be what it was (or even close) before seating the bullet - because the brass has yielded.

Now, as the brass gets worked/fired more and more without annealing, the brass gets harder. A fundamental rule of metalurgy is that when a metal gets harder, it gets stronger and it's yield strength increases. For that reason, the amount of "possible" neck tension is going to increase as the brass gets used more without annealing. How much? Don't know, haven't run the testing.

Lastly, if you want a smaller mandrel, why not chuck the mandrel in your drill and spin the mandrel in a piece of emory cloth or fine(ish) grit sandpaper. Say 320-440 grit or so? You should be able to peel .001 or .002 off in a couple minutes this way. </div></div>

I agree that the case neck ID would no longer be .300", because for the bullet to have gotten into the neck when you seated it, EITHER the bullet had to "compress" to .300" (not possible, since the bullet is much harder to compress than the neck wall is to stretch!), or the neck wall had to stretch to accommodate the .308" bullet.

BUT, there is no question in my mind that stretching the neck wall requires FORCE, and that after the stretch, there is RESIDUAL force, since the brass is NOT "inelastic", but rather "elastic". This HAS to be so. otherwise, there would be NO force required to extract the bullet from the case or depress the bullet into the case. We know that force IS required to do either. In fact, this is why the bullet does not set back into the case during recoil in a bolt rifle or seniauto rifle, and during feeding in a semiauto rifle.

I think most people would agree that the tighter the interference fit, the more the neck wall brass is stretched, and the higher that residual force becomes.

So, even though extracting the bullet after seating it would show a neck ID greater than what the neck was sized to, I still maintain that the MORE you stretched the neck, the higher the neck tension.

The only question in my mind is how much neck tension is SUFFICIENT for a semiauto 308. A number of authors experienced with semiauto 308s, and also cognizant no doubt about potnetial liability and therefor cautious, have suggested that .003" or .004" neck tension is more suitable for a semiauto. .002" is the smallest number I have seen. I tend to be prefer to be safe than sorry, and I doubt that an extra .001" to .002" neck tension would make or break the accuracy. I could be wrong. But I don't want to blow up my rifle via a set back bulelt creating higher than planned pressures.

Jim G
 

turbo54

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Re: Neck tension question

The maximum amount of possible neck tension occurs when you yield the brass.

Consider torqueing a bolt. A bolt is nothing more than elastic clamp for a joint. The maximum acheivable clamp force is when the bolt is torqued to yield. As you crank on the wrench, you can feel the bolt getting tighter and tighter up to a point, where the torque required to rotate the bolt flatlines, then drops.

My point is that MAXIMUM possible neck tension has been achieved when you can pull the bullet, and the caseneck is measurably larger than it was before seating the bullet. I dont know that exact number, but its less than you think. Brass is not very stretchy - especially in the annealed condition.
 

TexIndian

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Re: Neck tension question

I've often wondered what the 'stretch limit' was for a neck - how far you could go before you exceeded the ability of the brass to stretch and entered the area where you were permanently resizing the neck. I've always figured it depended on several factors, incl. the neck wall thickness, the properties of the particular alloy mix used in the brass, and number of firings since last annealing. Once you go beyond the limit, it seems to me that 'neck tension' would remain constant no matter how far you go (within limits).

I use the Sinclair expanders that Turbo mentioned. (The turning mandrels are marked with a T and the expanders have an E.) I start new brass with an expander since they are usually way too small, plus this gives me a perfect circle in the I.D. I agree with Turbo that this step puts any neck irregularities on the O.D. and gives you an I.D. that is concentric with the case body (and hopefully the bore). One thing I've noticed is that different brands of new brass will give slightly different results after coming off the mandrel. The length time I leave the mandrel in the neck is one factor, but I think the factors listed above are all in play, too.

I just finished running 500 new .308 cases each of Lapua and Win brass through the mandrel and the Win cases were consistently a tad smaller than the Lapua when I finished - maybe .0005 or so. It's hard to get an exact I.D. measurement without some really expensive tools, but when you try to run the cases over a turning mandrel (after expanding) you can tell a definite difference between brands. Assuming both brands are freshly annealed and that my technique was consistent, that only leaves the thickness and properties of the brass to account for the difference (oddly enough, the Win necks are a couple thou thinner). I routinely run into the same thing when choosing a sizing bushing. It may be that there is not a hard line where the brass stops stretching and starts yielding, but rather there is a zone where both things are happening at the same time. In any event, I have always found a bit of guesswork when trying to predict the results of any sizing step. Life was a lot simpler when all I owned were some basic dies and a set of plastic calipers.
 

TexIndian

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Re: Neck tension question

I should add that I always figured there was a bit more than .002 of stretch in a typical neck. Don't ask me why or how much. I use the expander mandrel for my bolt and AR guns, but for the M1As I always felt I needed more tension just because of the reputation of that gun for having a violent action. For those rounds I use a FL Redding die w/ neck bushings and the optional carbide expander. The expander still gives me the perfect I.D. like the mandrel, and by using bushings I can avoid all that yanking a standard die will give you. By playing around with bushings, I can usually get around 3 or 4 thou of tension. Since I usually run thicker brass in those guns, I figure they'll give me the extra tension. But maybe it's a placebo. I don't really know.
 

Country

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Re: Neck tension question

To neck turn cases you start with the neck turning operation.
Fora new case you size it and then use a neck expander mandrel that is just a fraction larger than the neck turner mandrel.
This then gets the case toa neat no slap fit on the turner mandrel. Turn the neck down to a skim clean up of about 75% of the nenck area for a factory . Once this is done then resize the case necks to take a bullet or seat a bullet if they are tight enough as is . Then measure the case neck diameter and subtract your amount of neck tension required to find your bushing. .001 for hand fed one at a time target work .002 for general shooting and hunting . .003 for bigger bullets and Autos. .004 for big ammo in autos .
Once you have done this don't change the setting of the neck turner .
 

JimGnitecki

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Re: Neck tension question

I did some measuring via digital caliper last evening. Very interesting results.

First, Federal Gold medal 308 175g comes with only .0019" neck tension. Hornady 175g comes with about .0026". These have funcitoned well in my LMT MWSE semiauto, so I guess .002" neck tension IS enough.

But here's the really interesting part. I measured my pre-firing and post-firing handloaded Lapua cases.

The pre-firing neck wall thickness was .0159" (consistently) and post-firing neck wall thickness is .0160", again consistently.

The neck OD of the brand new Lapua cases was .3364" (very consistently).

I used a .336" bushing in my Redding sizing die.
This implies projected neck tension = .336 - .308 bullet - 2 x .0159 wall thickness = .0038".

However, the actual measured neck OD after bullet is seated is .338", not .336". So, neck tension actually is .0018", not .0038" as planned.

I guess the case stretches enough furing the bullet seating operation to gain .002" in diameter.

That makes sense, as the case wall thickness of only .0159" is no match for the solidity of the .308 bullet, and one of them HAS to give when they are forced togetehr in an interference fit.The .002" gain in neck diameter is only .002 / circumference of the .338 circle = .002 / 1.0619 = two-tenths of one percent.For virgin annealed brass, that is not hard to do.

The case neck epxands during firing to "fill the rifle chamber", and then relaxes just a bit. The measured neck OD after firing in MY rifle is .3456". This is consistent with the post-firing OD I got with both the Federal Gold medal and the Hornady.So, the case neck diameter of the Lapua cases was expanded by .009" during firing, because the chamber in my rifle is that diameter (or a bit more I guess)at the neck, since it is a semiauto rifle and MUST feed reliably with no chance of firing out of battery or bullet setback.

The case diameter just below the shoulder grew .0028" and near the base it grew .0039", after shrinking back a bit after firing. This seems reasonable too.

I learned too that my combinaiton of chamfering via Wilson / Sinclair trimmer with chamfering tool with micrometer set for 2.005", followed by HAND deburring with the Wilson hand tool, must have been, in inadequately controlled COMBINATION, too agressive. I say this because the case OAL actually SHRUNK between virgin and post-firing length by an average of .005", and varied by .0115" from shortest to longest! I think I did the chamfering right, using the micrometer and locking the setting. But, that hand deburring must have been aggressive enough to not just deburr, but to actually "encounter" the chamfer. Once it encountered the chamfer, any subsequent additional "deburring" became aggressive (because then deburring a "knife edge" surface), and unpredictable and unmeasured, SHORTENING of the case length! That could not have been good for consistency, so it is a msitake I will not repeat. From now on, ONE turn of the deburring tool only!

I don't know whether to stay with the .336" bushing, or to go to a .335" bushing to get just a bit more neck tension (closer to .0028" than the current .0018"). I can't see .0028" being too MUCH neck tensino for a semiauto, and it would set my mind at ease on preventing bullet setback in a fully loaded magazine or during feeding.

Opinions?

Jim G
 

The Mechanic

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Sep 9, 2006
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San Diego County Ca.
Re: Neck tension question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JimGnitecki</div><div class="ubbcode-body">I did some measuring via digital caliper last evening. Very interesting results.

First, Federal Gold medal 308 175g comes with only .0019" neck tension. Hornady 175g comes with about .0026". These have funcitoned well in my LMT MWSE semiauto, so I guess .002" neck tension IS enough.

But here's the really interesting part. I measured my pre-firing and post-firing handloaded Lapua cases.

The pre-firing neck wall thickness was .0159" (consistently) and post-firing neck wall thickness is .0160", again consistently.

The neck OD of the brand new Lapua cases was .3364" (very consistently).

I used a .336" bushing in my Redding sizing die.
This implies projected neck tension = .336 - .308 bullet - 2 x .0159 wall thickness = .0038".

However, the actual measured neck OD after bullet is seated is .338", not .336". So, neck tension actually is .0018", not .0038" as planned.

I guess the case stretches enough furing the bullet seating operation to gain .002" in diameter.

That makes sense, as the case wall thickness of only .0159" is no match for the solidity of the .308 bullet, and one of them HAS to give when they are forced togetehr in an interference fit.The .002" gain in neck diameter is only .002 / circumference of the .338 circle = .002 / 1.0619 = two-tenths of one percent.For virgin annealed brass, that is not hard to do.

The case neck epxands during firing to "fill the rifle chamber", and then relaxes just a bit. The measured neck OD after firing in MY rifle is .3456". This is consistent with the post-firing OD I got with both the Federal Gold medal and the Hornady.So, the case neck diameter of the Lapua cases was expanded by .009" during firing, because the chamber in my rifle is that diameter (or a bit more I guess)at the neck, since it is a semiauto rifle and MUST feed reliably with no chance of firing out of battery or bullet setback.

The case diameter just below the shoulder grew .0028" and near the base it grew .0039", after shrinking back a bit after firing. This seems reasonable too.

I learned too that my combinaiton of chamfering via Wilson / Sinclair trimmer with chamfering tool with micrometer set for 2.005", followed by HAND deburring with the Wilson hand tool, must have been, in inadequately controlled COMBINATION, too agressive. I say this because the case OAL actually SHRUNK between virgin and post-firing length by an average of .005", and varied by .0115" from shortest to longest! I think I did the chamfering right, using the micrometer and locking the setting. But, that hand deburring must have been aggressive enough to not just deburr, but to actually "encounter" the chamfer. Once it encountered the chamfer, any subsequent additional "deburring" became aggressive (because then deburring a "knife edge" surface), and unpredictable and unmeasured, SHORTENING of the case length! That could not have been good for consistency, so it is a msitake I will not repeat. From now on, ONE turn of the deburring tool only!

I don't know whether to stay with the .336" bushing, or to go to a .335" bushing to get just a bit more neck tension (closer to .0028" than the current .0018"). I can't see .0028" being too MUCH neck tensino for a semiauto, and it would set my mind at ease on preventing bullet setback in a fully loaded magazine or during feeding.

Opinions?

Jim G</div></div>

A collet bullet puller, your press, and a fish scale in lbs.
smile.gif
 

JimGnitecki

Sergeant
Full Member
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Oct 24, 2011
561
11
Austin, TX
Re: Neck tension question

You are right - I need to measure the actual bullet retention force, and then pull the bullet and measure the neck ID BEFORE firing.

I have a postal scale good to 30 pounds, and also the Hornady collet bullet puller, and my Harrell press.

I could push the bullet into the scale surface until it moves. Then, I coudl pull it using the collet puller, and measure the neck ID AND also the bullet diameter after seating and extraction.

So, let me see what I find, and report back . . .
smile.gif


is a 30 lb scale capacity enough? I THINK I have read somewhere that bullet retention forces of 25 to 90 lb are ideally required or desired, depending upon caliber and other variables.

Jim G
 

The Mechanic

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Re: Neck tension question

if you have the die set up at its highest leverage point you should have more than enough. If it pulls to easy just move the die to a point where you get some good scale deflection.
 

JimGnitecki

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Oct 24, 2011
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Austin, TX
Re: Neck tension question

Today, I used the Postal scale to try to check the neck tension in the cartridges described above (.336 sizing bushing, .338" loaded diameter with cases of .0159" neck wall thickness >> resulting in .0038" interference fit but only .0018" actual net interference after bullet is seated).

My postal scale only accepts up to 30 lb. I pushed the tip of the bulelt into the scale platform harder and harder, trying to see the digital reading that would result in the bullet setting back into the case.

Never got there! I hit 29.5 lb and stopped trying so that I would not exceed the capacity of the scale. I rechecked the COAL after the attempt, and there was ZERO movement.

I guess .0018" "net" (after stretch) neck tension is enough.

Jim G
 

X-fan

Sergeant
Full Member
Minuteman
Re: Neck tension question

That is what I thought would happen, but I have had mixed results with neck tension. I ultimately resorted to pushing a bullet in (between my hip and work bench) to get a feel for where I am at. Not very scientific.

I would think brass hardness would have a lot to do with pull out strength as well.
If you fire a case 10 times (without annealing) will you have more or less neck tension?
I do know you get a lot more grip with a case cleaned in stainless media as opposed to corncob.

Would be interesting to see what actual weight difference you get from hard to annealed brass.

Great thread and comments btw.

Peace
 

JimGnitecki

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Oct 24, 2011
561
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Austin, TX
Re: Neck tension question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: The Mechanic</div><div class="ubbcode-body">Extend your press handle. More leverage. </div></div>

No, you don't understand. I hit the limit of the scale.

I know I could apply more force, but I wouldn't be able to MEASURE how MUCH it took to break the bullet loose, since I already hit the limit of the scale.

I have no trouble extracting bulelts from cases via the Hornady press collet type bullet remover.
smile.gif
I just wanted to try to find out how much force it actually takes.

Jim G