How to check I have a safe level of neck tension

[SGK]

Hi

I'm doing my first lot of reloading. I turned the necks of my fire-formed .308 brass rather conservatively with a good amount of "low-side" untrimmed brass visible. I got the turner set to achieve about 0.0146" versus an initial target of 0.0145". My target was calculated from a sample of 50 neck wall thickness measurements so as to shave about 75% of the samples. While I could have shaved more off I decided to stop there. A bushing size of 0.336 was selected/purchased based on my target thickness (0.308 + 2x0.0145 - 0.001 = 0.336).

I was planning to follow Berger's recommendation for getting into the very rough zone for seating depth - loading 6 rounds for each of 90, 50 and 10 off the lands with a conservative powder load (6% below max listed in my Hornady loading manual for Varget and 168gr ELD-M). I just loaded the first six, at the deepest seating.

With a good deal of low side showing I'm now a bit nervous that I won't have enough neck tension. With these first 6 rounds there's obviously a large amount of bearing surface seated and the bullets certainly aren't falling out. But I thought it good sense to check with your experience before I go any further.

Thanks in advance for the guidance

Steve

 

[retired]

target rounds vs hunting ammo or self defense ammo
target can have very lite neck tension, esp when close to the lands.
not sure how the 50/90 lots will behave but they are "safe".

you did not list the type of brass, nor the type of rifle

 

[SGK]

Thanks for the reply.

These are target bullets, but shooting a Blaser R8 Professional Success (standard barrel) rather than a fancy match rifle which is still on my wish list.

I cycled the "10 off" rounds through my magazine (I had to remove the little rubber pad Blaser places in the trigger/mag housing) and they fed ok and were ejected, several times, without changing length. Of course I could seat the bullet deeper by simply pushing a round against a solid object.

I just want to make sure I'm safe and not doing anything stupid - thanks.

Yeah Berger recommend testing 130 off as well. http://www.bergerbullets.com/getting-the-best-precision-and-accuracy-from-vld-bullets-in-your-rifle/ I decided to skip that one. Of course a lot more testing needs to follow this broad one.

I do intend to load for hunting (much later) later. I assume more neck tension is sensible. But how much more?

 

[Shaggy357]

If the bullets fall out, your tension is too loose. If the bullets shave going in, the tension is too tight.

Sorry, couldn't help myself.

Neck thickness and neck hardness have a bearing on the amount of springback and neck tension. You need to turn the brass to make the neck concentric so the tension is more even around the diameter of the bullet. To get down to the nitty gritty of tension, you would need to know your customer chamber dimensions, bullet diameter, case neck thickness, and use bushing dies to make everything fit just right.

You will get some replies....you only need enough neck tension to hold the bullet in place so the powder doesn't fall out.....you need enough neck tension to keep the bullets in the magazines from backing into the case upon recoil....you need enough tension for the powder to ignite properly......you need enough tension so the bullet doesn't stick in the barrel when you remove the loaded round.....They are probably all correct, with the right gun and load.

Need more specifics to really get into neck tension. Just getting the cases concentric is a great start for an off the shelf firearm.

 

[SGK]

Hi shaggy357, a lot of what you ask for is in the first post. Yes, I could have turned the necks thinner for more consistency and concentricity. I stayed conservative for this first go. I can strive for better when I move to new brass after I have gotten the hang of things. I don't have the dimensions of my chamber (except I think I have a decent estimate of headspace given the limits of case expansion). I guess I could measure the external diameter of my unsized fired cases and compare that with what they have been sized down to and add that to the list of observations I'm keeping.

I'd just rather ask a perhaps dumb question than have a major screw up sitting by myself at the range. Sounds like I'm ok to proceed.

 

[fguffey]

You will get some replies....you only need enough neck tension to hold the bullet in place so the powder doesn't fall out.....you need enough neck tension to keep the bullets in the magazines from backing into the case upon recoil....you need enough tension for the powder to ignite properly......you need enough tension so the bullet doesn't stick in the barrel when you remove the loaded round.....They are probably all correct, with the right gun and load.

Need more specifics to really get into neck tension. Just getting the cases concentric is a great start for an off the shelf firearm.

And now all there is to do is measure neck tension; I can not help you because I have tension gages; problem, my tension gages measure in pounds. For that reason I go with bullet hold because there is no conversion for tensions to pounds.

F. Guffey

 

[Fred B.]

From my own testing, virgin brass (like Lapua) sized with bushing has 0.0004-0.0006 bounc back. So your bushing does not give you 0.001 neck tension, it gives you 0.0005 tension.
I use the same rule for my fired brass to determine if it's annealed too much (less bounce back) or not enough (more bounce back).
Just MHO.

 

[dellet]

And now all there is to do is measure neck tension; I can not help you because I have tension gages; problem, my tension gages measure in pounds. For that reason I go with bullet hold because there is no conversion for tensions to pounds.

F. Guffey

I think I am beginning to understand the concept of bullet hold, but I have a couple of questions.

How do you differentiate between how much "hold" the bullet has on the neck, vs how much "hold" the neck has on the bullet?

Because if the bullet has all the hold, the neck diameter or length should not matter.

Is there a formula to determine how much "hold" a bullet has?

Isn't actually the neck that "holds" onto the bullet, instead of the bullet that "holds" onto the neck?

 

[SGK]

I took a quick look at some of my untouched fired brass. Just quick n dirty measurements with callipers accurate to +-.5 thou. It was quite consistently 0.345-0.346”. That’s not a chamber dimension but of brass formed to the chamber and then cooled. Unsurprisingly my recently loaded rounds measured 0.337 given the bullets all measured 0.308. So I guess I will have a release dimension just a bit more than 8-9 thou. That doesn’t say anything about bullet hold tension but perhaps provides a little more data for interpretation?

Fred B, I suppose this is an area I don’t fully I understand yet. My brass is never going to compress the bullet. But it has a natural desire to return to a steady state and that grips the bullet. That same factor creates “bounce back” when the brass is squeezed by a bushing. But is it it really going to have more tension on the bullet if I used a smaller bushing? Perhaps initially but after quite some time gripping that immovable object, the bullet, surely the brass forms to it and that extra tension eases? I would have thought the ‘springiness’ of the brass only dependent on its structure (‘annealed status’ to choose a label). In that case the bushing just needs to do ‘enough’ (post bounce back) as any more is wasted (and detrimental due to overworking the brass). Then the question is whether the one thou less bounce back in my case is enough or should I really add another thou.

(I hope the above is at least coherent.)

 

[SGK]

Dellet, I understand it this way. We use brass in essence because of its stretchiness. Stretch the brass neck around a bullet and that stretchiness (desire to return to its previous dimension) grips the bullet. Less neck to bullet bearing surface contact lowers the amount of grip the neck has.

What I’m wondering is there is simply a finite amount of bounce back which is dependent on hardness (or annealed status) of the brass. Compressing it more beyond a certain point and then stretching it around the same object doesn’t achieve more tension?

My thread question was really just focused on whether I had things safe for the range. But Fred B has made an interesting point. I then ask would a bushing 1 thou less actually lead to more tension? What about 2 thou less versus the one thou less?

 

[SGK]

So I guess I will have a release dimension just a bit more than 8-9 thou.

Oops, need to divide by two (and of course the case neck will change thickness slightly as it expands)

 

[mikecr]

While you're bushing downsizing >5thou the sizing amount is usually more than stamped on the bushing. That is, your sized neck diameter is likely less than you'd expect from your bushing selected.
So, you're probably producing 1thou of interference fit or more.
Measure this, what your sizing is actually producing. Let us know from there.

 

[SGK]

The exterior neck dimension of a bunch of resized cases (from which I was loading) is 0.336. This is the bushing I used/own.

(I took fired cases, neck sized them with a Lee collet neck die, expanded them with the 21st Century expander die 'n mandrel, hopefully largely transferring neck thickness inconsistencies to the exterior dimension, turned the necks as described above and then neck sized with the .336 bushing. Were the necks turned to perfect thickness consistency the tension would be consistent. Because of my conservatism in turning I will have variance in neck tension and maybe even less tension than one thou as some of the brass neck is slightly thinner than 0.0145" although balanced also by leaving the high side at about 0.0146".)

 

[jr600yd]

SGK.... before your head explodes with all this info take a deep breath. First what do you want the rifle to do? From your posts it sounds like you want the rifle for hunting and maybe some target practice. Competition may be in the future but with a separate target rifle. OK, your trying to get the best accuracy out of the rifle you have that’s a good thing. Accuracy, how accurate is accurate for what you want to do? Lots of medium size game have fallen to 1-2inch groups. I know I know you want better than that and your working in the right direction.

Neck tension: your working with a hunting rifle not a Benchrest rifle. The dimensions of your chamber are not known. You want enough grip on the bullet so recoil doesn’t force the bullet deeper into the case. My guess (since it’s a 308) your hunting range will be inside 300 yds (I may be wrong ). Go with .003-.004 neck tension the game will not know the difference and you’ll sleep easier at night.

 

[retired]

too much

SGK.... before your head explodes with all this info take a deep breath. First what do you want the rifle to do? From your posts it sounds like you want the rifle for hunting and maybe some target practice. Competition may be in the future but with a separate target rifle. OK, your trying to get the best accuracy out of the rifle you have that’s a good thing. Accuracy, how accurate is accurate for what you want to do? Lots of medium size game have fallen to 1-2inch groups. I know I know you want better than that and your working in the right direction.

Neck tension: your working with a hunting rifle not a Benchrest rifle. The dimensions of your chamber are not known. You want enough grip on the bullet so recoil doesn’t force the bullet deeper into the case. My guess (since it’s a 308) your hunting range will be inside 300 yds (I may be wrong ). Go with .003-.004 neck tension the game will not know the difference and you’ll sleep easier at night.

 

[Fred B.]

I had a 6ppc with about (less) 1 thou neck ID under .243. Shot excellent .
Only problem I had was i was jamming bullet and once I had a bad primer; ejected the case and spent an hour cleaning powder from action, trigger.
I will never use less than 1 thou with jumping bullet.
In your case, what you might see is a mini shoulder on the neck if the bushing does not re-size the entire shoulder (which almost never does). It will help center the case in chamber neck and and gives you room for doughnut.

 

[243winxb]

Measure the neck diameter before and after seating a bullet. After seating, has the neck expanded .002"

 

[dellet]

SGK, my question was to Mr. Guffey because he has a certain way about doing things I would like a better explanation of.

Your question was about safety, the best answer is it depends. How close is your load to maximum? What type of action are you shooting it in? Are you using the correct powder?

With a published load, you probably can't get enough neck tension from sizing the neck on a bullet to be a safety issue. Most likely you would crush the neck before you could get a bullet started down it, if it had enough interference to cause a safety issue. The other possible way would be to crimp it enough so it's easier to release the pressure out the back of the chamber than push the bullet out the front.

Neck tension or hold is all about an interference fit. The smaller the hole, the more interference there is, the tighter the fit, the more pressure it will take to get the bullet moving.

Bushing numbers represent the amount of interference you will have. . The amount and quality of surface contact of neck and bullet will also play a role. So when people say they have .002" of tension, they are really talking about the amount of interference fit there is between the neck and bullet.

If you need more than .004" of interference to hold a bullet in place in all but the roughest of conditions or actions, there is probably something else going on. So measure a loaded round at the neck to get your brass thickness as described before

Then there is the mystery of neck tension as it relates to accuracy/precision and that's a rabbit hole of another sort.

 

[mikecr]

Neck tension or hold is all about an interference fit. The smaller the hole, the more interference there is, the tighter the fit, the more pressure it will take to get the bullet moving.

This is not true at all with bushing(partial neck) sizing. Here, tension amounts only to an area of neck spring back (grip force) against seated bullet bearing. Seating forces created by sizing to excess interference fit, and/or excess friction, contributes nothing to tension.

Partial length size a neck down to produce ~1thou under cal after springback.
Partial length size a neck down to produce ~10thou under cal after springback.
Seat bullets in both, measure seated neck diameters, then pull those bullets, and measure your necks again. They both measure the same, which is ~1thou under loaded diameter.
Sizing down an excess (~10thou under) was negated when you then used a bullet as an expander mandrel(not good by the way). And you end up with ~1thou of springback gripping either bullet either way.

If you want to adjust tension while partial length sizing your necks, you do so by adjusting length, or area that will be springing back against (gripping) your bullet bearing. When you run out of this adjustment due to bushing reach or short seated bearing length, you've run out of adjustment.

FL sizing of necks brings additional tension situations into play. Donut tension, extending shoulder support, base binding,, none of them are 'good'.

 

[dellet]

This is not true at all with bushing(partial neck) sizing. Here, tension amounts only to an area of neck spring back (grip force) against seated bullet bearing. Seating forces created by sizing to excess interference fit, and/or excess friction, contributes nothing to tension.

Partial length size a neck down to produce ~1thou under cal after springback.
Partial length size a neck down to produce ~10thou under cal after springback.
Seat bullets in both, measure seated neck diameters, then pull those bullets, and measure your necks again. They both measure the same, which is ~1thou under loaded diameter.
Sizing down an excess (~10thou under) was negated when you then used a bullet as an expander mandrel(not good by the way). And you end up with ~1thou of springback gripping either bullet either way.

If you want to adjust tension while partial length sizing your necks, you do so by adjusting length, or area that will be springing back against (gripping) your bullet bearing. When you run out of this adjustment due to bushing reach or short seated bearing length, you've run out of adjustment.

FL sizing of necks brings additional tension situations into play. Donut tension, extending shoulder support, base binding,, none of them are 'good'.

Good point. I was speaking in very general terms.

I believe that there is always a point of diminishing returns, as well as a window of adjustment. If this were not true groups would not change with adjustment of fit.

Always open to correction.