Neck sizing and tension

rick539

rick539

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Mar 2, 2010
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#1
Not new to reloading, but new to precision reloading. After hours and hours of reading and videos, kind of came up with a game plan and would like some input.

Plan on a Forester full size bushing die. Use a bushing to get neck tension to 0.003”, then use a mandrel die to open up to 0.002” of neck tension. I would hope this would help with concentricy and work any deformities out of the neck.
Input? Thanks
 
#2
rick539 said:
Not new to reloading, but new to precision reloading. After hours and hours of reading and videos, kind of came up with a game plan and would like some input.

Plan on a Forester full size bushing die. Use a bushing to get neck tension to 0.003”, then use a mandrel die to open up to 0.002” of neck tension. I would hope this would help with concentricy and work any deformities out of the neck.
Input? Thanks
Click to expand...
To see any results from the mandrel I think you will need to go down .004 and then back up to .002. Any less and it doesn't really do anything but kiss the brass. That said, this is a much debated topic. I personally tested it extensively and with brass that's already been 2x fired in my chamber, the mandrel didn't show up on target or in SD/ES compared to bushing sizing. That's not the experience of everyone though so do it if you want to but I would size it down more than 1 thou past where you want to end up and I think that's pretty much agreed on in the community . There's another thread on this topic active already you might want to check out
 
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#3
Many times an expanding mandrel may be a better idea if going .003 on the bushing. The turning is .002 less than bullet vs .001 with expanding. The .001 with spring back should yield .015 tension or so. Now results may very and .015 may or may not be enough tension depending what your using
 
#7
rick539 said:
So, should I go with just a non bushing fl die then use the mandrel. What is the average neck tension a straight fl die give.
Click to expand...
I personally wouldn't do that. Full length bushing sizing die is what you want. Just a matter of if you are going to use a mandrel or not, and then what size bushing depending on if you want to mandrel it up or what not
 
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#8
rick539 said:
So, should I go with just a non bushing fl die then use the mandrel. What is the average neck tension a straight fl die give.
Click to expand...
This is what works for me. I remove the decapper. Then use a mandrel to set the interference fit. .0015-.002. I anneal every firing to alleviate brass hardening. I find RCBS FL dies give .004-.0045 under caliber size. Redding .003-.0035
 
#9
rick539 said:
So, should I go with just a non bushing fl die then use the mandrel. What is the average neck tension a straight fl die give.
Click to expand...

It’s designed to give .002” when you use the supplied decamping/expanding assembly, but a mandrel produces better concentricity and it’s easier to acquire different sizes to get the bullet seating pressure perfect.
 
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#10
Like said already the bushing/mandrel will be most consistent. The idea is to not overwork the brass as well

However if your chasing small movements of brass and most consistent tension you will have to anneal eventually
 
#11
Ok, let me get this straight. I have new alpha casings. Outside diameter is .291. Wall thickness is .014. This gives me an inner hole diameter of .263, which is .001 of tension. If I use a .288 bushing, this would give me .004 of neck tension. If I ran a .262 mandrel, this would give me my .002 neck tension (not accounting for spring back). Would this be over working if they were annealled.
 
#12
rick539 said:
Ok, let me get this straight. I have new alpha casings. Outside diameter is .291. Wall thickness is .014. This gives me an inner hole diameter of .263, which is .001 of tension. If I use a .288 bushing, this would give me .004 of neck tension. If I ran a .262 mandrel, this would give me my .002 neck tension (not accounting for spring back). Would this be over working if they were annealled.
Click to expand...
Assuming your measuring outside diameter of your neck with bullet seated?

Take outside diameter with bullet seated. Subtract .003. Use that size bushing. Then expander mandrel as another step. Gives about .015 tension. Annealed every time

This is what I did
 
#13
rick539 said:
Ok, let me get this straight. I have new alpha casings. Outside diameter is .291. Wall thickness is .014. This gives me an inner hole diameter of .263, which is .001 of tension. If I use a .288 bushing, this would give me .004 of neck tension. If I ran a .262 mandrel, this would give me my .002 neck tension (not accounting for spring back). Would this be over working if they were annealled.
Click to expand...

No.

Overworking is taking a 308 case whose neck expanded to 345, FL sizing it down to 328, and then expanding it back out to 335. Add up the amount of brass movement.

In your case you’ll be sizing down from 297 to 288 and expanding back out to 290. That’s nothing in comparison. A standard FL die will take the neck down to 284. That’s still less than what 30 cal dies are doing
 
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#14
If you anneal your cases every firing then it almost doesn’t matter whether you use a regular FL die with the expander ball removed, a bushing die alone, or follow either with a mandrel.

That said, I still use a mandrel because I think my stuff comes out slightly better when using one.

But, it can be argued that the main thing the mandrel does is just fix up any mouths/necks that might have got banged out of whack while tumbling off the sizing lube (which happens more than most know until they look for it). If you’re not going to wait to do the mandrel step until after you’ve tumbled the lube off, then I wouldn’t even bother with one.
 
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#16
Ronin22 said:
Do all bushing dies cause donuts? I might have an irrational fear of donuts...J/K
Click to expand...
Depends on your definition of donut.

All with a neck only bushing will leave an unsized ring of brass at the neck base due to the chamfer in the bushing.
If you get a neck/shoulder bushing that only a few boutiques die makers offer then they will size it all the way down.

If by donut you mean an actual thickness of neck material building up due to brass migration then the bushing doesn’t have any influence on that factor.
 
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#17
New here. Try not to throw stones at me. The concept of neck tension was introduced to me yesterday. I'm gathering you would measure diameter of an existing neck with a projectile seated to get a starting point?
 
#19
hafejd30 said:
Like said already the bushing/mandrel will be most consistent. The idea is to not overwork the brass as well

However if your chasing small movements of brass and most consistent tension you will have to anneal eventually
Click to expand...
New. Don't throw rocks at me. Learning here lol. Why would you have to anneal? We are assuming that the brass would experience greater stress during the sizing and then mandrel die usage? Or is to prevent future stresses on the brass?
 
#20
BuildingConceptsllc said:
That's right. Of course it needs to he the brass you will use and bullet but yes.
Click to expand...
Vaugley, what is the process? Measure neck tension on current brass with bullet seated (my stuff that I am shooting) and then measure after sizing to see what the difference is? Somewhere in the .002 range? I understand that neck consistent neck tension is desirable to make sure that the bullet releases from the brass the same way each time. Just don't know the rest.
 
#21
Roblj4 said:
New. Don't throw rocks at me. Learning here lol. Why would you have to anneal? We are assuming that the brass would experience greater stress during the sizing and then mandrel die usage? Or is to prevent future stresses on the brass?
Click to expand...
Brass gets work hardened from firing/sizing. Making spring back and what not more likely when sizing. Thus giving inconsistent neck tension. Annealing softens the brass to make it consistent
 
#22
hafejd30 said:
Brass gets work hardened from firing/sizing. Making spring back and what not more likely when sizing. Thus giving inconsistent neck tension. Annealing softens the brass to make it consistent
Click to expand...
That makes much more sense. So annealing can assist with consisten neck tension and spring back of brass. Thank you
 
#25
Roblj4 said:
Is there an accurate way to do this without a dedicated annealer? I know, dumb question. New to the concept.
Click to expand...
Not really in my opinion

You want consistent temp/time. Some do it with a drill and socket. There’s many that overheat brass or not heat enough to accomplish anything

Whatever method you choose I’d use tempilaq to check your results. I run 750 in the neck, 650 below the shoulder and 400 mid case. To make sure I’m getting to temp but not compromising my case head by heating it up. Hence the 400° tempilaq.

I run dual torches on a bench source. Not saying it can’t be done in a simpler fashion but the biggest thing is it’s consistent and actually annealing
 
#26
hafejd30 said:
Not really in my opinion

You want consistent temp/time. Some do it with a drill and socket. There’s many that overheat brass or not heat enough to accomplish anything

Whatever method you choose I’d use tempilaq to check your results. I run 750 in the neck, 650 below the shoulder and 400 mid case. To make sure I’m getting to temp but not compromising my case head by heating it up. Hence the 400° tempilaq.

I run dual torches on a bench source. Not saying it can’t be done in a simpler fashion but the biggest thing is it’s consistent and actually annealing
Click to expand...
Understood. Thank you. I will start looking into annealers.
 
#27
Roblj4 said:
Measure neck tension on current brass with bullet seated (my stuff that I am shooting) and then measure after sizing to see what the difference is? Somewhere in the .002 range?
Click to expand...

Yeah you’ve got it, it's pretty easy. There are a few ways to go about this, but this is the simplest
  1. Measure the OD of a loaded round, in this example you should have something like 0.294"
  2. Determine your desired "neck tension", say 0.002", & subtract it from the above OD.
  3. Choose a bushing/mandrel combination that will size the OD of unloaded brass to this diameter. In this example, you'd be looking for 0.292" OD on your unloaded, sized brass
above edited - I typed out my mental model for neck tension, which isn’t really correct

Some more info

Roblj4 said:
Is there an accurate way to do this without a dedicated annealer?
Click to expand...
x2 on @hafejd30, no. Also, if you over anneal, that brass is trash. You cannot recover it.
 
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#28
R_A_W said:
It's pretty easy. Assume you're loading 6.5 Creedmoor in Lapua brass.
  1. You measure the neck thickness of your unloaded brass (e.g. Lapua 6.5cm is 0.015"), write that down.
  2. Load a complete round using your normal process & measure the OD of the neck on that loaded round (say you get 0.292"), write that down.
  3. You then take that OD measurement & from it subtract 2x the brass neck thickness. In this example, you would have 0.292" - (2 x 0.015") = 0.262"
  4. Subtract that number from the bullet diameter. In this example, the 0.262" subtracted from the 0.264" bullet diameter would mean you have 0.002" of "neck tension".


x2 on @hafejd30, no. Also, if you over anneal, that brass is trash. You cannot recover it.
Click to expand...
Understood. I'll give this a try. Thanks for the info.
 
#30
R_A_W said:
I responded while I was on a phone call... I retyped the above, please reread.

Neck tension is somewhat a misnomer, you're really looking for "interference fit".
Click to expand...
Understood. I reread it. Is this the measurement you need to take to order the expander mandrel die? I saw an order form that requires a similar measurement. I'll give this a try and report back.
 
#31
I’m not sure… I use a Porter Precision Products, their “starter kit” (or whatever they call it) comes with 5 or 6 different diameter mandrel.

There are a lot of factors that will impact the sizing of brass, like thickness, hardness, lubrication from carbon deposits… it’s not something that I try and calculate in order to only have 1 neck bushing & 1 mandrel.
 
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#33
Roblj4 said:
Understood. I reread it. Is this the measurement you need to take to order the expander mandrel die? I saw an order form that requires a similar measurement. I'll give this a try and report back.
Click to expand...
The outside loaded round diameter is for a bushing that tells you how much smaller it makes it sizing down from the outside.

For the mandrel diameter you will want an inside measurement so you can either 1) take the outside diameter from before and subtract the brass thickness or 2) order whatever the amount smaller than your bullet diameter.
 
#34
Roblj4 said:
Vaugley, what is the process? Measure neck tension on current brass with bullet seated (my stuff that I am shooting) and then measure after sizing to see what the difference is? Somewhere in the .002 range? I understand that neck consistent neck tension is desirable to make sure that the bullet releases from the brass the same way each time. Just don't know the rest.
Click to expand...
I see @spife7980 answered your question already but as far as a mandrel goes you really have to test it yourself. For me, 2thou under (.2440" for 6cm )works great and is enough neck tension to keep the bullet from moving during transport or clambering ect... I do a little more than that for my .223 ar rounds though because of the beating they take.

So back to the 6cm: I use a .270 bushing and a .2440" mandrel, and thats with a Berger 108/109 bullet and lapua brass. I think I tried .2424, and .2431 also when I was doing all of the mandrel testing which is basically 3 thou and 3.5thou under and I went with the .2440.

I will also tell you about some other tests that I've done. I tested 2x or more fired brass doing just the bushing and no mandrel VS bushing and mandrel and I saw no difference in SD or on target. Now everyone does not have that same experience/opinion, but many do. I only use a mandrel to fix a dented neck or something after I fire the brass 2x.

My mandrel doesn't really expand the brass much when I use a .270 bushing, which is why think it didn't show any difference. I just said that to say that, the mandrel may or may not even be necessary for you, so just try it out and see. I think almost everyone at least with lapua brass uses one of .269, .270, or .271 bushing for 6mm though so take that into consideration.
 
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#35
Reviving this thread a little...

I have come to realize the enormous importance of neck tension in precision shooting. I was wondering if there is a rule of thumb when it comes to just how much neck tension is needed vs just personal preference.

For example, with my 300PRC my MV is averaging 2972 with a 230gr Berger HOTM. I am targeting a .001-.0015 simply because my case is almost full and figure that the light neck tension will help manage chamber pressure. Having said that, i am also wondering if there could be some pressure leaks with that combination as well.

In a scenario like the one above, would i be better off with more neck tension than less?

For my precision work, i am not shooting from a magazine. If i do plan to shoot from a magazine, i would increase neck tension. I also have a 6.5 creedmoor in both a bolt and AR-10. As above, for my bolt, i practice a neck tension of .001-.0015 and for my AR, i target .002. For my bolt gun, i am pushing a 140gr Berger with an average MV of 2910 and my AR has an average MV of the low 2800s. I keep my bolt and AR ammo separate.

Thoughts?
 
#36
I always target .0015 for mine. 308 and 260 mainly. My 300 shot great at that as well. If it doesn’t like that I try to shoot for around .003. I’ve found more of the magnums like my 338 Lapua seemed to prefer a touch more neck tension. My fclass 284 runs about .002

For my large frame AR’s I had issues using the same .0015-.002 tension. When I sent the bolt home or fired the rifle the next round would extend its overall length. The bolt mass coming forward was working like an impact bullet puller.
 
#38
GunnyUSMC said:
Reviving this thread a little...

I have come to realize the enormous importance of neck tension in precision shooting. I was wondering if there is a rule of thumb when it comes to just how much neck tension is needed vs just personal preference.

For example, with my 300PRC my MV is averaging 2972 with a 230gr Berger HOTM. I am targeting a .001-.0015 simply because my case is almost full and figure that the light neck tension will help manage chamber pressure. Having said that, i am also wondering if there could be some pressure leaks with that combination as well.

In a scenario like the one above, would i be better off with more neck tension than less?

For my precision work, i am not shooting from a magazine. If i do plan to shoot from a magazine, i would increase neck tension. I also have a 6.5 creedmoor in both a bolt and AR-10. As above, for my bolt, i practice a neck tension of .001-.0015 and for my AR, i target .002. For my bolt gun, i am pushing a 140gr Berger with an average MV of 2910 and my AR has an average MV of the low 2800s. I keep my bolt and AR ammo separate.

Thoughts?
Click to expand...
IMHO, neck tension with less than .002 isn't a good idea, mainly because of the violent action for chambering a round that would tend to change the bullet's seating depth. Though, the lighter the bullet, the less this is an issue.

For my two bolt guns, I've found that .0015" neck tension works really well. But I wouldn't say that works in every gun. I've tried .0025 to .001 and found the .0015 to work the best (this is for .308 and 6.5 PRC). I don't feel there's a particular neck tension that works the same for every gun. One needs to experiment and find out which does for the particular gun much the same way as finding the right seating depth for best performance.

Too much neck tension, like .004 or more can be a problem for getting good consistent seating depths. . . . especially when neck interference (the friction between the two surfaces) can add to the problem.
 
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#41
hafejd30 said:
For my large frame AR’s I had issues using the same .0015-.002 tension. When I sent the bolt home or fired the rifle the next round would extend its overall length. The bolt mass coming forward was working like an impact bullet puller.
Click to expand...

I tested my 6.5 and 308 and found the bullet always moved forward unless I crimp it. I’ve been using a Lee factory crimp die and a heavy crimp to stop movement. I keep loads for my AR10’s separate from loads for my Origin.
 
#42
For me, .002 is not enough; many folks are finding that neck tensions between .001and .002 result in inconsistent seating pressures. However, if you bump that NK tension up to around .003, you start to find that seating pressures are much more consistent. You can test this for yourself.
 
#44
Bit of a tangent but someone argue with me. For neck tension I putzed around with bushings, dealt with donuts, on and on. I just had Forster hone me FL dies 4thou under neck diameter with a bullet seated. Pulled the ball and stem out of the die. Neolube then a K&M .0025 mandrel. Neolube again, charge the case, seat the bullet. Could only find .001 of runout and SD on ten shots dropped from 8 to 5.4fps. Is it the amount of neck tension or the consistency of the neck tension that matters?
 
#45
Xferbuckeye said:
Bit of a tangent but someone argue with me. For neck tension I putzed around with bushings, dealt with donuts, on and on. I just had Forster hone me FL dies 4thou under neck diameter with a bullet seated. Pulled the ball and stem out of the die. Neolube then a K&M .0025 mandrel. Neolube again, charge the case, seat the bullet. Could only find .001 of runout and SD on ten shots dropped from 8 to 5.4fps. Is it the amount of neck tension or the consistency of the neck tension that matters?
Click to expand...
It's ALL about consistency. :giggle:
 
#46
Xferbuckeye said:
Bit of a tangent but someone argue with me. For neck tension I putzed around with bushings, dealt with donuts, on and on. I just had Forster hone me FL dies 4thou under neck diameter with a bullet seated. Pulled the ball and stem out of the die. Neolube then a K&M .0025 mandrel. Neolube again, charge the case, seat the bullet. Could only find .001 of runout and SD on ten shots dropped from 8 to 5.4fps. Is it the amount of neck tension or the consistency of the neck tension that matters?
Click to expand...
For 10 shots I wouldn't consider 8 and 5.4 diffrent really.
 
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