Neck Tension - Bushing and Mandrel Sizes?

[222Jim]

Folks,

As fall approaches and I review my results (which I'm happy with, but we all know we can do better), I'm beginning to ponder how I select the bushing and mandrel size I use (trying) to set neck tension. Your feedback and thoughts would be appreciated.

Here's the situation. After I've fired my .22-250, the case neck outer diameter (OD) is 0.2520". Given it's a (i) 0.2240" diameter bullet, (ii) I want 0.0020" of neck tension, (iii) the neck wall thickness is 0.0130, and (iv) I'm assuming 0.0010" of spring back, I use a 0.2470" bushing die to compress the neck, i.e. 0.2240 - 0.0020 + 0.0130 + 0.0130 - 0.0010 = 0.2470". That gives me a 0.2210" ID before spring back.

I then use a 0.2220 mandrel die to stretch open the case mouth, thereby (hopefully) easing out any wall thickness variations before seating the bullet.

My query is, given the fact that final "mandrel sizing" is within the elastic deformation range for brass, is the brass simply going to return to where it was once I extract the mandrel? And if so, shouldn't I be using a smaller ID bushing die before inserting the mandrel so as to get the expansion closer to or just in the plastic deformation range for brass?

Thanks

Jim

 

[JohnW...ski]

Sounds pretty much how I load my ammo with the exception of annealing, I usually anneal every second reloading with good results. I believe the annealing makes the spring back less and also more consistent.

John

 

[Bill Norris]

Folks,

As fall approaches and I review my results (which I'm happy with, but we all know we can do better), I'm beginning to ponder how I select the bushing and mandrel size I use (trying) to set neck tension. Your feedback and thoughts would be appreciated.

Here's the situation. After I've fired my .22-250, the case neck outer diameter (OD) is 0.2520". Given it's a (i) 0.2240" diameter bullet, (ii) I want 0.0020" of neck tension, (iii) the neck wall thickness is 0.0130, and (iv) I'm assuming 0.0010" of spring back, I use a 0.2470" bushing die to compress the neck, i.e. 0.2240 - 0.0020 + 0.0130 + 0.0130 - 0.0010 = 0.2470". That gives me a 0.2210" ID before spring back.

I then use a 0.2220 mandrel die to stretch open the case mouth, thereby (hopefully) easing out any wall thickness variations before seating the bullet.

My query is, given the fact that final "mandrel sizing" is within the elastic deformation range for brass, is the brass simply going to return to where it was once I extract the mandrel? And if so, shouldn't I be using a smaller ID bushing die before inserting the mandrel so as to get the expansion closer to or just in the plastic deformation range for brass?

Thanks

Jim

Spring back will be determined by the amount of movement of the bushing pushing inward when the mandrel is pushed into the case. The bigger the difference between the bushing and mandrel the more spring back you will have normally.

 

[Coyotefurharvester]

222 do all the case mouths "feel" the same when you mandrel them? I like to size a couple thou smaller than my mandrel size, and let the mandrel rest in the case mouth a few seconds.

 

[JFrank]

I sized these over a month ago with a .261 bushing. I would not factor in much spring back.

 

[PopCharlie]

The math is right. I set tension using the same math. Are you annealing? It really helps setting consistent neck tension. Also, are you lubing the neck before running them over the mandrel? I found that cleaning the lube out after mandrel sizing with acetone make a big difference with the "feel" of bullet seating. You can feel the brass yield point. If you use a force pack, you can measure it as well.

PopCharlie

 

[mikecr]

Your spring back is more like 1/2thou max.
You would be better to go .223 mandrel size, and not go smaller bushing.

 

[jepp2]

but we all know we can do better), I'm beginning to ponder how I select the bushing and mandrel size I use (trying) to set neck tension. Your feedback and thoughts would be appreciated.

Seems like I am always needing just one more bushing or mandrel to get exactly what I want. My math skills are acceptable, but sometimes you don't get exactly what your numbers suggested. As long as that doesn't cause you an issue, you will be fine.

 

[Webster]

Folks,

As fall approaches and I review my results (which I'm happy with, but we all know we can do better), I'm beginning to ponder how I select the bushing and mandrel size I use (trying) to set neck tension. Your feedback and thoughts would be appreciated.

Here's the situation. After I've fired my .22-250, the case neck outer diameter (OD) is 0.2520". Given it's a (i) 0.2240" diameter bullet, (ii) I want 0.0020" of neck tension, (iii) the neck wall thickness is 0.0130, and (iv) I'm assuming 0.0010" of spring back, I use a 0.2470" bushing die to compress the neck, i.e. 0.2240 - 0.0020 + 0.0130 + 0.0130 - 0.0010 = 0.2470". That gives me a 0.2210" ID before spring back.

I then use a 0.2220 mandrel die to stretch open the case mouth, thereby (hopefully) easing out any wall thickness variations before seating the bullet.

My query is, given the fact that final "mandrel sizing" is within the elastic deformation range for brass, is the brass simply going to return to where it was once I extract the mandrel? And if so, shouldn't I be using a smaller ID bushing die before inserting the mandrel so as to get the expansion closer to or just in the plastic deformation range for brass?

Thanks

Jim

I keep things simple. I bought 4 steel bushings to cover a range I thought I needed. I ended up using just one. I wouldn't buy nitrided bushings they are very expensive and I don't find any need for them. I was involved with lubrication and failure analysis for many years. They are not self lubricating. Ten years of sizing with plain steel bushings without a problem. I lightly lube the necks.

Never used a mandrel, it seems like an unnecessary step for my needs. I shoot a 6BR for BR and varmint hunting. Groups under .400". I don't need any development or testing work. I am happy with the rifle and reloads as they are. Some people say a mandrel makes the ammo more concentric? I really don't care and don't want to find out. Seems strange to use a bushing that's too small then open it up with a mandrel. How many bushings and mandrels would you buy to get the correct tension? If you have several calibers you could end up with 25-50 bushings and mandrels. The mandrel is hanging by the press and die threads. I don't see how it can possibly be in any kind of alignment. Some guys that measure run out say mandrels definitely help. I really don't care. Getting out in the field and eliminating varmints is all I care about.

Evening out wall thickness variation? You cannot change the variation; you’re just moving it around. If you want small groups don't go cheap on a barrel. Buy something like a Kreiger, Brux, Bartlein, Shilen, Hart and have a very good gunsmith chamber it.

 

[Bc'z]

I keep things simple. I bought 4 steel bushings to cover a range I thought I needed. I ended up using just one. I wouldn't buy nitrided bushings they are very expensive and I don't find any need for them. I was involved with lubrication and failure analysis for many years. They are not self lubricating. Ten years of sizing with plain steel bushings without a problem. I lightly lube the necks.

Never used a mandrel, it seems like an unnecessary step for my needs. I shoot a 6BR for BR and varmint hunting. Groups under .400". I don't need any development or testing work. I am happy with the rifle and reloads as they are. Some people say a mandrel makes the ammo more concentric? I really don't care and don't want to find out. Seems strange to use a bushing that's too small then open it up with a mandrel. How many bushings and mandrels would you buy to get the correct tension? If you have several calibers you could end up with 25-50 bushings and mandrels. The mandrel is hanging by the press and die threads. I don't see how it can possibly be in any kind of alignment. Some guys that measure run out say mandrels definitely help. I really don't care. Getting out in the field and eliminating varmints is all I care about.

Evening out wall thickness variation? You cannot change the variation; you’re just moving it around. If you want small groups don't go cheap on a barrel. Buy something like a Kreiger, Brux, Bartlein, Shilen, Hart and have a very good gunsmith chamber it.

Hallelujah, preach brother preach!!

 

[searcher]

I keep things simple. I bought 4 steel bushings to cover a range I thought I needed. I ended up using just one. I wouldn't buy nitrided bushings they are very expensive and I don't find any need for them. I was involved with lubrication and failure analysis for many years. They are not self lubricating. Ten years of sizing with plain steel bushings without a problem. I lightly lube the necks.

Never used a mandrel, it seems like an unnecessary step for my needs. I shoot a 6BR for BR and varmint hunting. Groups under .400". I don't need any development or testing work. I am happy with the rifle and reloads as they are. Some people say a mandrel makes the ammo more concentric? I really don't care and don't want to find out. Seems strange to use a bushing that's too small then open it up with a mandrel. How many bushings and mandrels would you buy to get the correct tension? If you have several calibers you could end up with 25-50 bushings and mandrels. The mandrel is hanging by the press and die threads. I don't see how it can possibly be in any kind of alignment. Some guys that measure run out say mandrels definitely help. I really don't care. Getting out in the field and eliminating varmints is all I care about.

Evening out wall thickness variation? You cannot change the variation; you’re just moving it around. If you want small groups don't go cheap on a barrel. Buy something like a Kreiger, Brux, Bartlein, Shilen, Hart and have a very good gunsmith chamber it.

For casual varminting - you are right - no need to do this. And, as you say, you are just "
moving the brass around", but the idea is to create more uniform tension and pushing a little of the ill-located brass to the outside, as will improve concentricity as measure on bullet runout. I think most guys (like me), don't use a threaded press, but rather an arbor press with the expander "free floating" in the die body. And you are also right about how many bushings and expanders one can end up with - lots! One thing I have noticed when using the nitrided bushings is you get a different measurable outcome as opposed to using the steel bushing. Lots of mandrels and bushings make quick changes convenient when maintaining consistency between different brass lots, etc. The alternative is to turn your necks to fit your bushings - which doesn't always work out satisfactorily.

 

[Ned Ludd]

Rather than using a lot of extra (and in my opinion unnecessary) thickness and/or diametral measurements, I make the mandrel diameter choice relative to the bullet diameter and the desired neck tension/interference fit. I find this approach much simpler easier. In my hands, a mandrel that is .0015" under bullet diameter will yield very close to .002" neck tension...as long as...a bushing was used to size the neck that yields a diameter of at least .001" smaller than the mandrel will leave it. That way, the mandrel will do work on all the necks and a consistent springback of very close to .0005" will be the result. So the mandrel diameter of .0015" under bullet diameter plius an extra .0005" springback = ~.002" neck tension. If the bushing leaves the neck too close in size to the diameter the mandrel will yield, the results may well be inconsistent and it just doesn't seem to work as well in my hands.

For example, if I was using a bushing die as the sole sizing step for Lapua .308 Win cases and I wanted .002" neck tension, I know from past experience that a 0.336" bushing is what I want. If I then wanted to add the use of a mandrel as the final sizing step, I would first use a 0.335" bushing, followed by opening the necks up with a 0.3065" mandrel (i.e. .0015" under bullet diameter). The extra ~.0005" gained from springback as the mandrel was withdrawn would then bring the total neck tension very close to .002". Of course, we know that numbers stamped on bushing are not always true, but this is assuming the selected bushing gives the correct sizing. Likewise, I would use a 0.248" bushing with Lapua .223 Rem brass as the sole neck sizing step to yield ~.002" neck tension. Alternatively, I would use a 0.247" bushing and a 0.2225" mandrel to achieve approximately the same neck tension.

This approach can be used to select the appropriate mandrel diameter and bushing size for pretty much any desired neck tension relative to bullet diameter. However, one also needs to know what size bushing by itself would yield the desired neck tension, so the correct bushing can be chosen that is small enough to allow the mandrel to do some work when opening back up the necks in the final sizing step. Fortunately, it seems more common for reloaders to add a mandrel sizing step after they have been using a bushing die alone for some period, so they usually already have this information when they decide to go the mandrel route. Does this approach require extra work? Yes, it does. However, I am absolutely convinced that adding the mandrel as the final sizing step yields more consistent neck tension, resulting in better precision and more uniform velocity. If I wasn't convinced, I wouldn't be doing it. Nonetheless, everyone is free to test and decide for themselves what steps in the reloading process they deem necessary and unnecessary.

 

[Mulligan]

Neck Tension

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...

forum.accurateshooter.com

This is a good discussion on neck tension

CW

 

[dgeesaman]

I like your bushing selection for reaching a .002 neck tension without a mandrel operation. I’d go down to .246 or even .245 to ensure a little bit of plastic deformation during the mandrel op.

If you’re not annealing frequently then maybe your process with less cold work is beneficial, and I have found that the mandrel can help with uniformity even if it’s only stretching out the slightly undersized necks and not reshaping all of them.

One note: I have found bushings to vary quite a bit from their printed size. Mandrels not so much. I’ve found both rcbs and Redding bushings to be within a few tenths (+/-) of their nominal size. Other brands can be off by a solid thou. So mic your bushings and/or stick to the same big name brand so that you’re getting legitimate .001 changes between bushing sizes.

 

[222Jim]

222 do all the case mouths "feel" the same when you mandrel them? I like to size a couple thou smaller than my mandrel size, and let the mandrel rest in the case mouth a few seconds.

I hold the mandrel in place for ~5 seconds. Most cases feel the same when I push the mandrel in, but occasionally I find it unusually easy or tough to push the mandrel is. I've checked wall thickness and there's nothing unusual.

 

[222Jim]

The math is right. I set tension using the same math. Are you annealing? It really helps setting consistent neck tension. Also, are you lubing the neck before running them over the mandrel? I found that cleaning the lube out after mandrel sizing with acetone make a big difference with the "feel" of bullet seating. You can feel the brass yield point. If you use a force pack, you can measure it as well.

PopCharlie

I anneal (AMP) every time I reload.

 

[222Jim]

I like your bushing selection for reaching a .002 neck tension without a mandrel operation. I’d go down to .246 or even .245 to ensure a little bit of plastic deformation during the mandrel op.

If you’re not annealing frequently then maybe your process with less cold work is beneficial, and I have found that the mandrel can help with uniformity even if it’s only stretching out the slightly undersized necks and not reshaping all of them.

One note: I have found bushings to vary quite a bit from their printed size. Mandrels not so much. I’ve found both rcbs and Redding bushings to be within a few tenths (+/-) of their nominal size. Other brands can be off by a solid thou. So mic your bushings and/or stick to the same big name brand so that you’re getting legitimate .001 changes between bushing sizes.

Bushings...............I ordered a set from 0.242 to 0.250. I was very frustrated when the 0.244 and 0.245 bushings gave me exactly the same OD. I was able to return them and get two new ones.......

 

[Mastershot]

I use a hydro press, this is the only way to tell how much neck tension you have.

 

[JFrank]

What I find more important than mandrel vs bushing is not assuming one particular size is better than another because someone said so. It’s just too easy to test this stuff on a target and far too important, the node doesn’t really change but the group size damn sure does.

 

[222Jim]

Folks,

As fall approaches and I review my results (which I'm happy with, but we all know we can do better), I'm beginning to ponder how I select the bushing and mandrel size I use (trying) to set neck tension. Your feedback and thoughts would be appreciated.

Here's the situation. After I've fired my .22-250, the case neck outer diameter (OD) is 0.2520". Given it's a (i) 0.2240" diameter bullet, (ii) I want 0.0020" of neck tension, (iii) the neck wall thickness is 0.0130, and (iv) I'm assuming 0.0010" of spring back, I use a 0.2470" bushing die to compress the neck, i.e. 0.2240 - 0.0020 + 0.0130 + 0.0130 - 0.0010 = 0.2470". That gives me a 0.2210" ID before spring back.

I then use a 0.2220 mandrel die to stretch open the case mouth, thereby (hopefully) easing out any wall thickness variations before seating the bullet.

My query is, given the fact that final "mandrel sizing" is within the elastic deformation range for brass, is the brass simply going to return to where it was once I extract the mandrel? And if so, shouldn't I be using a smaller ID bushing die before inserting the mandrel so as to get the expansion closer to or just in the plastic deformation range for brass?

Thanks

Jim

For an alternative view, I asked my mechanical engineer step-daughter about this. She's not a shooter, but does work in a metal fabrication shop and works with different metal alloys.

She sent me a stress-strain curve for 260 Grade Brass (also known as "cartridge brass"), which happens to be what most cases are made from. Her main point was that you need to stretch the brass by at least roughly 0.0020 of an inch to get out of the "elastic range". That's NOT stretching it by 0.0020" in diameter but 0.0020" in circumference. If you don't go beyond a 0.0020" stretch in circumference, the brass simply returns to its original shape/size. Beyond that, it's "plastic". So here's the math:

1. A .2240 bullet has a circumference of 0.7038" (0.2240 x 3.14159, a.k.a. diameter times pi),
2. Stretch that by 0.0020" means the circumference is 0.7058",
3. Doing the math backwards, that means the diameter is now 0.2247, and thus
4. Anything changing the ID by 0.0007" (0.2247 - 0.2240) is just enough to make that change "sort of" permanent.

Sort of? Spring back is due to the fact the stress-strain curve isn't flat, but the further you move up from the 0.0020"/200MPa point on the curve, the less the spring back.

Other interesting points she raised:

1. When I try to decide how much tension I want on the bullet, remember that there's only a marginal increase in real (force) tension beyond 0.0010 of neck tension, as we shooters know it, because the case neck is entering the plastic range (0.0010" diameter change = 0.0031" circumference change), and
2. If I try for 0.0005" tension, the case neck brass was only stretched by 0.0016" when I seat the bullet and the case neck is still in the elastic range. Given how step the stress/strain curve is, along with normal brass metallurgical quality inconsistencies, the actual "force" tension holding the bullet can vary a lot.
3. So, for my .222 Remington and .22-250 Remington, her input was it's best to stick between a minimum of (what she called "shooters neck tension") 0.0010" and a maximum of 0.0020". Little benefit beyond, and potential inconsistencies below.