Neck Tension vs Accuracy

[jlow]

Isn’t this .002, 0.003, 0.004 neck tension purely theoretical?

I find that due to spring back and work hardening, what you actually get is always less and not particularly predictable. Have you guys actually measured neck diameter, neck thickness, and actually calculated ID?

 

[johara1]

Isn’t this .002, 0.003, 0.004 neck tension purely theoretical?

I find that due to spring back and work hardening, what you actually get is always less and not particularly predictable. Have you guys actually measured neck diameter, neck thickness, and actually calculated ID?

I anneal every time , yes i measure everything to the .0001 and it is very predictable……. jim

 

[jlow]

Agreed that annealing every time helps to even things out but still those neck tension numbers are not what is actually holding the bullet. Unless the case is annealed dead soft, which is not what we want, even a properly annealed case will have spring back.

 

[snakepit]

I agree with TOM and Alex that tension is critical. Some guns are more critical then others. I also like to shoot the VLD's 10 to 15 in and I believe both of these help reduce vertical at 1000 yards. The more tension helps keep the bullet more consistent when going into the rifling. Plus the more tension helps if you have to open the bolt on a live round. Never had a bullet stay in the barrel. Matt

When you say more tension? I curious about what numbers you are talking, how much tension or how high have you gone to achieve the results you were looking for.

I was out load testing yesterday due to new dies and lot of powder. I found that my 6.5x47 definitely likes more than .002" neck tension. When I tried dropping down to .002 groups doubled. Loads area .002 off the lands.

Just as you said above, "how much tension or how high have you gone to achieve the results you were looking for". You stated more than .002" neck tension but what numbers are you talking about?

 

[jlow]

BTW, I don’t want to come across as elitist with these questions about actual neck tension. The way it is described right now is in fact how I have been describing it myself but more recent measurements have left me with numbers that don’t actually match what was expected and thus want to bring this up to see how others have dealt with it.

 

[johara1]

When you anneal is where you get spring back from…. I don't guess at anything, if the numbers don't match either your bushing is not the correct size or you may be doing or not doing something right. I have switched to the hydro seater and it has served me well, with numbers to the pound in seating force ….. jim

 

[jlow]

I use the K&M seating force measurements and my numbers are consistent so that is not the point of the discussion.

The point is if you use a specific bushing, let’s just say 248 for a 223 caliber, your external diameter of the case after you put it through the bushing will not be the same for every case. They may all be 0.248” if you round it to three digits but if you us a good quality micrometer that measures down to 0.00005” like a Mito, you will see variations. Since the busing ID is fixed, the only reason for this is variation in spring back which is affected at least by two things. One is the actual wall thickness of the case (thicker more spring back) and degree of work harden (more work harden, more spring back).

So going back to the original point, stating neck tension by the theoretical difference between bullet diameter and internal case diameter is problematic as it does not take into account the spring back which affects actual real internal case diameter.

So unless two people discussing this have the same type of case (metallurgy), have exactly the same neck thickness, the same degree of neck thickness variation, and the same degree of case hardening. That 0.002/0.003/0.004 can mean very different things.

 

[dkhunt14]

I anneal every time and the tension stays pretty close. I am not sure of numbers like the K&M dial gives but my guns responded by more tension and the way my arbor press handle feels when seating I can tell you it has more tension. I am always 2 plus by bushing numbers and I have a special die my friend made me that sizes not at all at the shoulder junction and has taper built into it towards the mouth. When I use this die there is lots of tension and I never let a bullet stick not even on a full jam. My WSM's seems to really like this. When I use a Reading bushing die I use at least 3 thousandths. Some of the short range BR guys told me they tune a lot by tension. Seeing they don't anneal they tighten up tension as cases get harder to stay in tune. If it matters at 100 yards it sure will matter at 600 or 1000. My buddy just told me both his Dasher and WSM got rid of vertical fliers and groups tightened up on when his numbers on his K&M arbor press went up. I told him I noticed the same thing but I don't have the dial setup on mine. I just noticed the handle pulls harder. Now I always shoot the bullets in the rifling and my guns got better this way. Matt

 

[dkhunt14]

Jlow neck thickness variations could also cause what you are talking about. I also think that if you use more tension the variations even out more. Matt

 

[jlow]

Matt - I think you are right and is the reason why some people crimps (not that I am suggesting we should crimp our precision rounds). Interestingly, some people go the other way i.e. no neck tension to avoid the problem. Personally, I think the best way is to know what variables cause the problem and address them without going to the extremes.

 

[mikecr]

Tension is not interference.
Actual tension = bullet grip = springback force
Springback is what's overcome to release bullets.

Annealing does not increase springback force, it decreases it, thereby decreasing bullet grip(tension).
The benefit is consistency, and most of this is in reduced tension which = reduced variance in it.
(this assumes perfect annealing)
Higher seating forces, or lower seating forces, from annealing, are due to reduced springback affecting interference fit one direction or the other(depending on last action, downsizing/expansion). And also change in ID friction.

There is no tool on the market which measures springback.
Seating force is the best we have right now, but is highly dependent on friction and interference for relative correlation to tension(neither equal springback).

Just throwin it out there because we don't need to go roundy with misconceptions.

 

[Alex Wheeler]

Tune with the bushing. Once you find it, stay with it. I try to anneal the same every time but the cases will come out of the die .0005" different sometimes. I assume this is from annealing as they come out pretty close within the same batch. Forget what the dial says, it is data, but I have shot 4s with over 10 lbs of seating force variation. Internal neck finish is what the dial is telling you, changing bushings has a small effect on seating force while internal neck finish has a huge effect. Bushing size is what seems to show on target not seating force.

 

[jlow]

Mikecr - Spring back is ability of metal to resist change. Work harden metal have more spring back but annealed metal is softer and have less spring back. However, for reloading, spring back is an interesting thing as it can both decrease neck tension but also increase neck tension…

The reason it can decrease neck tension is because if you size a neck with bushing, neck tension of the case reduce the actual decrease in neck diameter because the neck resist sizing and springs back to a larger external diameter and thus a larger internal diameter than what the bushing should theoretically give you.

The reason it can increase neck tension is because when you seat a bullet into that same neck, the more spring back it has, the more the neck wants to return to its original size and so the more squeeze on the bullet thus increasing neck tension.

Agree that seating force measurement does not measure just the force holding the bullet (spring back) as it also affects friction but I think friction is also involved in the release of the bullet when the round is fired.

Zfastmalibu – I think the inconsistency is partially due to different degree of annealing but also any slight difference in the thickness of the neck which also affects its ability to resist the sizing (spring back) but also the actual degree of movement of the neck that is possible if you are sizing with a LCD.

 

[Alex Wheeler]

My necks are +/- .00005" I don't think that is effecting spring back much.

 

[johara1]

jlow, First different neck tension gives you different seat depth. I do mine by the numbers, i don't trust how it feels. If in your statement the the slightest difference in neck thickness will change neck tension …… you are right.. but i turn necks my ES. is in single digits. I adjust neck thickness to tweak neck tension…… So now you tell me how in the world no turn necks shoot well? …………. jim

 

[jlow]

Jim, at least in my hands, modest difference in neck tension does not affect my seating depths although I have seen this at high neck tension and especially compressed loads. My seating depths usually varies by about a thousand. Agree doing things by the numbers, this is why I use the K&M seating force tool to measure my rounds.

I wish I could tell you how no turn necks shoots well….. It does not in my hands.

 

[johara1]

Jim, at least in my hands, modest difference in neck tension does not affect my seating depths although I have seen this at high neck tension and especially compressed loads. My seating depths usually varies by about a thousand. Agree doing things by the numbers, this is why I use the K&M seating force tool to measure my rounds.

I wish I could tell you how no turn necks shoots well….. It does not in my hands.


How uniformly you clean your neck inside also affect things. I can hold seating depth to .0005 and it lets me see differences. My K&M is in the drawer now that i have the hydro seater. Big pressure rings are a killer and a whole new ball game, you have .0005 spring back and when the pressure ring is .0005 larger than the shank what holds it?…………. jim

 

[mikecr]

The reason it can decrease neck tension is because if you size a neck with bushing, neck tension of the case reduce the actual decrease in neck diameter because the neck resist sizing and springs back to a larger external diameter and thus a larger internal diameter than what the bushing should theoretically give you.

Hard necks will spring back more from last direction sizing(which can be either direction). But this as a change only affects seating force, not tension. Think about it, annealed necks provide less springback, so they spring back less from down-sizing, increasing seating force(due to increased interference). But tension itself is reduced with annealed necks.

I think friction is also involved in the release of the bullet when the round is fired.

No it isn't.
I coat bullets with WS2 which is very slippery, and seating forces(or pull force if preferred) greatly decreases as a result of the coating. Yet MV changes none uncoated -vs- coated. This is I think a unique thing about WS2. It doesn't really affect a load(like moly).
And, it presents a reality that 'pull force' is meaningless to internal ballistics, until isolated specifically to that pull force caused only by springback.

Same holds true for squeaky clean necks -vs- carbon fouled. While seating forces are affected, velocity is not.
But as mentioned, changing actual springback(tension) is significant.

Spring back is ability of metal to resist change.

I'm not sure about this either. What you're describing is 'strength' or 'tensile strength' which represents an amount the metal can squeeze or stretch without yielding.
Springback in my mind represents energy stored(hardness), which brass tries to release, including over time.
A rubber case would have more springback than brass, but way less strength.

 

[jlow]

Hard necks that springs back more will have increase in tension on the bullet. It is not the differential size of the case and bullet that gives you tension – think about seating a bullet in putty, there is no spring back and no tension. It is harder to judge what happens to seating force since an annealed neck will gets more down sized but it has more give when the bullet is being seated.

I was of course describing what happens in general. If you coat your bullet with WS2, it will have less friction but the fact is given the same bullet with the same coating, it will have more friction when seated into a case that has not been annealed vs. one that has. Whether or not that increase in friction affects overall “neck tension” significantly really depends on how much your WS2 reduce friction.

The way I look at spring back really as a general term and so it is easy to poke holes in it but in the end, it is apples to apples and so looking only in terms of the ability of the same metal to resist change.

 

[mikecr]

No, annealed necks increase seating forces when you downsize only. This is why reloaders tend to think it 'restores' tension.
Reality, tension-wise, is just opposite. Annealing reduces tension either way.
Where annealed necks are expanded after downsizing, that's when folks decide that annealing reduces tension(based on then reduced seating forces).

It really is best though to recognize 'seating forces' as a sum of 'springback' + 'interference fit' + 'friction', with 'tension' being the springback portion only. More tests pass, and more solutions will be found with this.