Neck tension question

I am sizing 6x47 Lapua (.243) brass with Forster Full Length Resizing dies. After resizing, the neck is measuring .240 and not .243. Is the .003" okay or is that too much?

So the inside diameter of the case is .240”? If that is the case you should be fine. Normally you want .002” neck tension but it also depends on what your rifle likes. Most full length sizing does are a bit tighter than a bushing neck sizing die where you can adjust the neck tension based on the bushing used. If you are necking down from 6.5 you need to use a full sizing die to ensue the case and all of the neck are sized. Don’t use a neck bushing die to neck cases up or down because may not size the case properly.

RetiredArmyGuy said:

So the inside diameter of the case is .240”? If that is the case you should be fine. Normally you want .002” neck tension but it also depends on what your rifle likes. Most full length sizing does are a bit tighter than a bushing neck sizing die where you can adjust the neck tension based on the bushing used. If you are necking down from 6.5 you need to use a full sizing die to ensue the case and all of the neck are sized. Don’t use a neck bushing die to neck cases up or down because may not size the case properly.

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Yup...Inside the case is .240" and I am using a full-length resizing die. I am used to .001" or no deviation, so I wasn't sure. Thanks!

Yoshi said:

I am sizing 6x47 Lapua (.243) brass with Forster Full Length Resizing dies. After resizing, the neck is measuring .240 and not .243. Is the .003" okay or is that too much?

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How are you measuring the I.D. Are you using a caliper or go/no go gauges?

You can really get wacked out about this and then you will have to buy Redding bushing sizing dies. The problem then is that each batch of brass has a different thickness. So then you need more bushings and you have to keep your brass sorted to use the proper bushing.

If you are not shooting bench rest, don't worry about it.

The neck has to be smaller than the bullet, otherwise the case neck will have no purchase on the bullet and it will be free to slide up and down.

The most important thing to remember outside of benchrest shooting is all neck tension should be the same otherwise you will have accuracy issues over distance. This is a very simplistic answer but valuable lesson.

When different lots of brass have different neck thicknesses, you don't need different sizing bushings . You need a neck turning tool.

You can also turn the outside of the necks to keep them the same. Reaming will help get rid of donuts also.

Biggfoot44 said:

When different lots of brass have different neck thicknesses, you don't need different sizing bushings . You need a neck turning tool.

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^ This ^

Biggfoot44 said:

When different lots of brass have different neck thicknesses, you don't need different sizing bushings . You need a neck turning tool.

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I agree. I was just trying to make sure he wasn’t using a neck die with a bushing to neck the cases down to 6mm because that won’t work. I will be more clear next time I post.

Oh my. I came in here for massage tips.

Back to the OP's original question...is it OK? Short answer...yes...it'll be fine. And by fine I mean it'll be completely safe and most likely won't have accuracy issues that will effect 99% of the shooters out there. .003 is a touch on the more "grippy" side, but you may actually find it's better for your rifle/barrel. You'll still be producing ammo that'll be more precise than most anything you could buy.

All that said...neck tension / neck thickness does have an effect on the precision of the ammo you produce. Is it enough of an effect to make any difference? Well, that entirely depends on your abilities as a shooter and what your goals are. If you are shooting long range or benchrest, then you might start getting more concerned about it.

Also, shooters (reloaders particularly) tend to be OCD perfectionists. Knowing that there is something that could be tweaked / fixed / addressed to squeeze out a little more precision tends to drive us a bit crazy. Over time, we tend to acquire additional tools and adjust our reloading process to eliminate as much of the variance out of our shooting system as we can. The effect on our accuracy/precision? Probably mostly psychological...but we just can't escape trying to do everything we can to eliminate everything but us from the equation. So, for the sake of posterity and the education of new reloaders, let's go down this rabbit hole....

IMHO, I think there are two areas where neck tension matters (although to different degrees).

First, it effects the pressure curve of your ammo (as does how far you seat your bullet into the case & how much "jump" the bullet has to get to the lands and grooves). Hypothetically, let's assume that each case neck is exactly the same...the same thickness, the same length and the same hardness. Having more tension on the bullet does have a somewhat similar effect as say putting a crimp on your round. More tension = more pressure...all other things being the same. Different barrels react differently to slight variations in the pressure curve...and this is where tweaking comes in to find the combination that your rifle barrel likes best. Although, in my humble opinion...powder selection, powder weight consistency, case volume consistency and seating depth have a much greater effect than does +/- .001 of neck tension.

Secondly, variances in neck thickness and hardness will effect the uniformity of your neck tension. Now, this is where I think things start making a more noticeable difference. Precision is about reducing the variance in round to round, and even variance within the round itself.

In regards to round to round, some case necks will be a bit thicker and some a bit skinnier. If the reloader is using a bushing die or has removed the expander in a full length die, then the variance get's pushed to the inside of the neck and we get inconsistent tension from round to round. Which leads to inconsistent pressure, with leads to variance in speed, which leads to variance in vertical dispersion.

In regards to variances within the round itself, parts of the same case neck will be thicker than others. This is where things get even more interesting and when addressed most shooters see an impact on their group sizes. First, we need to discuss the concept of concentricity...or the perfect alignment of the axis of the bullet to the axis of the case to the axis of the barrel. When the round is not concentric, it will enter the barrel at a slight yaw, which theoretically can deform the bullet a smidge and transfer that slight yaw downrange. Several things effect concentricity, and inconsistent neck tension is one that goes largely ignored by most reloaders.

Many reloaders put in effort to keep the case in perfect alignment when reforming the case and when seating the bullet, so that once constructed the bullet is within x tolerance (usually =/- .005 for general ammo and +/- .003 or .002 for competition). Bushing dies, competition seating dies, tweaks to the press to get dies free floating, etc are all things people spend time and good money on to get things concentric...and they all work to varying degrees.

However even if the round is constructed concentrically, variations in the neck tension will lead to variations in how the bullet is released when fired and negate all of that good work (or some of it anyway). Some cases have as much as .003 variance in thickness from one side of the neck to another. This translates into one side of the neck being "grippier" than the other, leading to the release of the bullet being inconsistent and introducing that little bit of yaw we just spent a lot of time trying to get of. It can get even more pronounced on wildcat cartridges created from a chopped down parent cartridge where necks are created from case walls that have even greater variance in thickness than necks do typically (e.g. the 300 blk created from cut down .223 for example).

So, as others above have suggested, getting a reamer or an outside neck sizer / cutter are options people use to uniform the necks to achieve consistent thickness...which translates into more consistent tension.

AND...if you're going to this extreme...you should also consider annealing to uniform case neck hardness as this will effect the tension as well.

So, there you have it. A long winded explanation as to how neck tension can matter, and how to tweak and uniform neck tension from round to round and even within the individual round and why it matters. Which step is more important than the others and what makes the biggest differences? Opinions are varied. Does it matter enough to go through the expense / hassle? Each reloader has to answer that one for themselves.

Pretty good in depth response.... I'll just add that neck tension for my target gun matters a good amount. To the point where I will lube the neck prior to seating the bullet. Doing this has eliminated my vertical stringing.

Yes, I’ve heard that helps too. I’ve played around with chucking up a brass bore brush with a little bit of steel wool in a drill press and polishing the inside of the necks.

I’m not sure precision improved much, but I did notice that my “feel” when seating the bullet was more consistent and “smoother.”

Then again, some like to leave the inside of the case unpolished by media so that the carbon residue acts as a lubricant too.

That’s what I love about this hobby...it’s a never ending series of secret sauce and magic to try out