Neck Tension

[chkunz]

The amount of the interference fit between the bullet and the case neck is commonly referred to as "neck tension". I do not think that is the best technical term, but I will use it here to help with communication. So, using this definition, If I seat a 0.224 diameter bullet in a case with an internal neck diameter of 0.221 the result is 0.003 neck tension.

I have measured the expander ball on my standard Remmington 223 case resizing die and it is 0.223 and this gives me 0.003 or more neck tension depending on the spring back of the brass. With neck tension at 0.003 or greater it takes what I would subjectively judge to be considerable force to seat the bullet in the case. I have concerns that this level of force may do some damage to the bullet and may be detrimental to accuracy.

I have found that I can control neck tension by the use of the proper diameter expander mandrel. There are now good sources of expander mandrels in measurement increments of 0.0005 and with a little experimentation I can set neck tension at the amount I choose within the limitations of the variation of the spring back of the brass. This helps reduce the seating force and gives a much more consistent feel during the bullet seating process.

For a semi auto like the AR it is not recommended to go too low due to the risk of the bullet moving in the case during the dynamics of recoil and of the cycling of the action. So, I set neck tension between 0.002 and 0.003 for that application. For the single shot bolt action, I set it at approximately 0.001.

My question is, has anyone done any accuracy testing to see if there is any effect on accuracy due to variations in neck tension?

 

[Clancy]

I don’t turn necks unless I have to, I prefer to set my no turns up with .004 clearance.

That’s why I set my tension with a mandrel. I size down .004 below and then run a carbide mandrel that’s .001-.003 under, usually .002 unless it’s not satisfactory. This does a decent job of uniforming tension and it most definitely shows on paper.

When I do have to turn, I still turn for .004 clearance and size the same way, which makes tension as uniform as it’s ever going to get.

I have tested freshly annealed cases with and without turning and with and without the mandrel and the improvement is definitely linear in a positive direction the more steps I take.

I want good clearance, imperfections on the outside or nonexistent and low (but not too low) seating force.

People have been turning to the .0001 and annealing for decades. I think that’s many a thousand “ayes” for uniform neck tension.

In addition to that, check out some groups fired from custom muzzle loaders. They will all shoot in the .1s. Why? The absence of a case screwing things up is my opinion.

Bottom line, absolutely anything or everything you can do to make one case exactly like the other 4 in a string is going to show on paper. Uniform neck tension is near the top of that list.

 

[Bill Norris]

/\ /\ What he said.

 

[jackieschmidt]

/\ /\ What he said.

^^^^^
2d that.

 

[gunsandgunsmithing]

Just my 2 cents and we all know how much that is today. Neck tension is my very last step in fine tuning a load. Sometimes it makes a noticeable difference but often not. I think if you're jumping or jamming matters in this regard. I think that as long as you're jamming, but not enough to create a situation where closing the bolt changes seating depth, neck tension is very inconsequential..and most of my loads fall into that range in terms of seating depth. I think we get into an area where we have to determine if neck tension or bullet starting force into the lands is more important and which one happens first. Most of what I've read in regard to being jammed is that the case neck will open at a lower pressure than is required to start a hard jammed bullet to move. If that's the case, I think that's when neck tension is of very little value in tuning. Of course it's the other way around if you're jumping and the only thing holding the bullet back is neck tension. This is much of why I prefer to jam if the gun will allow it. It takes that variable out of my tuning and the results are there.
Notice I said "I think" to a few of these comments. That's simply because I don't feel comfortable stating it as fact but it is logical and it's common logic in short range br. I don't see how short or long range changes any of that, fwiw, Ultimately, do what the bbl wants but thinking things like this through may help someone in figuring out a methodical approach to tuning. Either way, I still find neck tension near the bottom in terms of things that matter most but there may be a reason for that if jamming and a reason against it if you typically jump.
Again, just my 2 cents..fwiw with Brandon's goons are running the show.

 

[Alex Wheeler]

In the long range game neck tension is huge. Its very important. Sure it needs to be uniform, but the amount is even more important. Once you have a decent load shoot groups with different amounts of neck tension and pick your bushing.

 

[Bill Norris]

Just my 2 cents and we all know how much that is today. Neck tension is my very last step in fine tuning a load. Sometimes it makes a noticeable difference but often not. I think if you're jumping or jamming matters in this regard. I think that as long as you're jamming, but not enough to create a situation where closing the bolt changes seating depth, neck tension is very inconsequential..and most of my loads fall into that range in terms of seating depth. I think we get into an area where we have to determine if neck tension or bullet starting force into the lands is more important and which one happens first. Most of what I've read in regard to being jammed is that the case neck will open at a lower pressure than is required to start a hard jammed bullet to move. If that's the case, I think that's when neck tension is of very little value in tuning. Of course it's the other way around if you're jumping and the only thing holding the bullet back is neck tension. This is much of why I prefer to jam if the gun will allow it. It takes that variable out of my tuning and the results are there.
Notice I said "I think" to a few of these comments. That's simply because I don't feel comfortable stating it as fact but it is logical and it's common logic in short range br. I don't see how short or long range changes any of that, fwiw, Ultimately, do what the bbl wants but thinking things like this through may help someone in figuring out a methodical approach to tuning. Either way, I still find neck tension near the bottom in terms of things that matter most but there may be a reason for that if jamming and a reason against it if you typically jump.
Again, just my 2 cents..fwiw with Brandon's goons are running the show.

I agree Bro. Neck tension is the last thing I look at with developing a load and most of the time I never get to that point before it is grouping well.

 

[gunsandgunsmithing]

In the long range game neck tension is huge. Its very important. Sure it needs to be uniform, but the amount is even more important. Once you have a decent load shoot groups with different amounts of neck tension and pick your bushing.

Aren't most people jumping in the long range game, though? In what little lr shooting I do, I've always been abole to find a jammed load that I like just as well as a jumped load, usually better. I prefer jammed for the reasons in my previous post. To each their own.

 

[gunsandgunsmithing]

I agree Bro. Neck tension is the last thing I look at with developing a load and most of the time I never get to that point before it is grouping well.

If all else is equal, I like the logic that I posted behind it. It wasn't my own but have read that for several years and it just makes sense to me. Granted, more and more people are going to thicker or no-turn necks altogether and I'm sure that can play a role as well.

 

[Alex Wheeler]

Aren't most people jumping in the long range game, though? In what little lr shooting I do, I've always been abole to find a jammed load that I like just as well as a jumped load, usually better. I prefer jammed for the reasons in my previous post. To each their own.

In the 6mm, most are in the lands. Theres two windows, .005-.008 in or so and .018-.024 in. Depending on what the barrel likes, and the bullet. Testing at 1k, the neck bushing size is night and day. Even just .001 either way. Probably the most overlooked thing in our game. In the .30s more guys do jump, but still theres a spot around .015 in they like too. And same thing, it matters big. I think it has to be tested at 1k if thats your game. I have tuned rifles at 600 that shot tiny but would not group at 1k until I changed the bushing size. I think it matters more the farther out you go.

 

[Clancy]

My long winded answer is based on thinking the question is about uniformity and not amount.

Alex is ALSO saying that amount matters greatly, and I think one might want to listen to him. I heard he has built and tuned some rifles that won a little bit and maybe set a record or two.

 

[dannyjbiggs]

Sorry...neck tension is the FIRST thing I attend to.

 

[Mulligan]

I am mapping out loads for a range trip later this week.
New barrel, new reamer, new bullets, fairly new powder.
Seating depth then neck tension, first, powder ladder to follow.
CW

 

[JMayo]

Hvy neck tension made my groups spread .... That's all i know....
BR ....

 

[Clancy]

 

[chkunz]

View attachment 1357137

Thanks to Clancy for directing the discussion back to my question.

 

[Mulligan]

Thanks to Clancy for directing the discussion back to my question.

Yes,
I have tested this. In my testing. However limited that may be, Some powders appear to have a preference for more or less neck tension.
After that initial test, I came to the conclusion that it needs tested each barrel/load work-up.
CW

Edit
I suppose I should add that I believe it is important enough that I bought a very nice set of mandrals for several calibers to test this with. I did not have enough bushings to adiquitley test it in my short range rifle (Waldog) so I ordered a set of mandrals from 21st for the little 22.

I will also admit, sometimes….not always, I get a wee bit better control using the mandrals to control neck tension. Most of the time the correct bushing works to perfection, but not always. My notes in my log include bushing and mandral for all comp rifles.
CW

 

[PracticalTactical]

The hard part in coming to a definitive conclusion with regard to any single variable in the reloading process is that we are always testing the sum result of all possible variables.

The biggest mistake we can make is assuming the variable we are thinking about is solely responsible for the results produced.

Additionally, something like the effect of neck tension is likely to vary depending on the cartridge and case capacity. The result of neck tension variation on a 223 for example is likely to create more of a variance than it would on a 308.

Having said that, it has always been my goal to minimize variation in neck tension as well as in minimizing variation of all other variables where practical.

I have developed a process for controlling neck tension that works well on un-turned necks and it involves incrementally sizing down starting with a bushing that is too big, and dropping a bushing size 0.001" at a time until the case will hold a round, then I go one size smaller.

I find this to be tedious obviously but does result in more consistent neck tension than using a single expander mandrel.

 

[chkunz]

The hard part in coming to a definitive conclusion with regard to any single variable in the reloading process is that we are always testing the sum result of all possible variables.

The biggest mistake we can make is assuming the variable we are thinking about is solely responsible for the results produced.

Additionally, something like the effect of neck tension is likely to vary depending on the cartridge and case capacity. The result of neck tension variation on a 223 for example is likely to create more of a variance than it would on a 308.

Having said that, it has always been my goal to minimize variation in neck tension as well as in minimizing variation of all other variables where practical.

I have developed a process for controlling neck tension that works well on un-turned necks and it involves incrementally sizing down starting with a bushing that is too big, and dropping a bushing size 0.001" at a time until the case will hold a round, then I go one size smaller.

I find this to be tedious obviously but does result in more consistent neck tension than using a single expander mandrel.

Thanks for the reply. I do not turn necks but control neck tension similar to what you describe. I would like to know if my efforts have any measurable effect on accuracy. I could do the testing and data analysis if I choose to do that, but it is a lot of effort since it takes a lot of data to define small changes. So, I thought I would see if someone else had done the testing and analysis even if it is on a different cartridge. I prefer data over opinions but sometimes opinions are all we have unless we are willing to do the testing. Thanks again for your reply.

 

[chkunz]

Yes,
I have tested this. In my testing. However limited that may be, Some powders appear to have a preference for more or less neck tension.
After that initial test, I came to the conclusion that it needs tested each barrel/load work-up.
CW

Edit
I suppose I should add that I believe it is important enough that I bought a very nice set of mandrals for several calibers to test this with. I did not have enough bushings to adiquitley test it in my short range rifle (Waldog) so I ordered a set of mandrals from 21st for the little 22.

I will also admit, sometimes….not always, I get a wee bit better control using the mandrals to control neck tension. Most of the time the correct bushing works to perfection, but not always. My notes in my log include bushing and mandral for all comp rifles.
CW

Great reply, thanks. I too bought bushings and mandrels of various sizes and they allow me to control neck tension very well but it is somewhat tedious especially with the variation in brass spring back. I would like to know if the effort is buying me anything in accuracy.

Do you have any accuracy vs neck tension data you would like to share?

Thanks again for you reply.