Neck tension - A different view

[Steff]

Until recently I have largely negated the influence of neck tension on accuracy. Party based on own experience ( I don‘t anneal) and also backed up by a test performed by Sead on the Accurate Reloading Forum.
I was right - and then again not.

The other week I brought 100 new Lapua .308 cases into operation which had been lying in my cupboard for 20 years. On seating the bullets for the test loads I noticed how tight the necks were. The test firing gave my quite severe vertical spreads, regardless of the charge weights. The trend was, 3 were perfect, 1 was 2“ low and one in between. Very unsatisfactory.

Remembering the tight bullet seating I ran the expander ball of my Redding neck sizing die without the bushing installed in and out of the rest of the yet unfired cases using some graphite.

Bingo, no more vertical spread. So my new theory is that high neck tension will indeed induce problems if it is not perfectly constant. On a lower level variations in neck tension have a negligible effect. A steep statement, but it reflects what I have seen so far.

 

[Smellydog]

I pulled a muscle in my neck last week. Really affected my shooting also. Couldn't seeanything much to my left!

 

[Steff]

I pulled a muscle in my neck last week. Really affected my shooting also. Couldn't seeanything much to my left!

Poor you. But I‘m talking about a load capable of 1/3 inch accuracy.

 

[Smellydog]

Poor you. But I‘m talking about a load capable of 1/3 inch accuracy.

Ohhhh , right, got ya

Yeah, if I get one in out of three I'm happy too

 

[Bowland blades]

Neck tension does matter but you wont see it so much if anything on deer

 

[User00044]

Until recently I have largely negated the influence of neck tension on accuracy. Party based on own experience ( I don‘t anneal) and also backed up by a test performed by Sead on the Accurate Reloading Forum.
I was right - and then again not.

The other week I brought 100 new Lapua .308 cases into operation which had been lying in my cupboard for 20 years. On seating the bullets for the test loads I noticed how tight the necks were. The test firing gave my quite severe vertical spreads, regardless of the charge weights. The trend was, 3 were perfect, 1 was 2“ low and one in between. Very unsatisfactory.

Remembering the tight bullet seating I ran the expander ball of my Redding neck sizing die without the bushing installed in and out of the rest of the yet unfired cases using some graphite.

Bingo, no more vertical spread. So my new theory is that high neck tension will indeed induce problems if it is not perfectly constant. On a lower level variations in neck tension have a negligible effect. A steep statement, but it reflects what I have seen so far.

I was under the impression that it's consistency that's important as opposed to the amount , when it comes to neck tension . By running the expander through the necks , you uniformed the neck tension and the effect was seen on target.

Totally agree with your findings.

 

[Steff]

I was under the impression that it's consistency that's important as opposed to the amount , when it comes to neck tension . By running the expander through the necks , you uniformed the neck tension and the effect was seen on target.

Totally agree with your findings.

Yes and no. I don‘t believe that I can produce high spec consistency just by running an expander through unturned necks. I also get very good results from brass on its 8th or more firing without ever having annealed or turned the necks. I put this down to a low neck tension level but with some inconsistencies.

 

[User00040]

Did you chamfer your case necks?

Not enough neck tension causes ignition issues.

US DoD spent a lot of time and money researching and developing ammunition for their sniper rifle systems. Their findings were that a slight crimp was beneficial across the board.

Maybe they should have just asked @Muir...

 

[User00044]

Yes and no. I don‘t believe that I can produce high spec consistency just by running an expander through unturned necks. I also get very good results from brass on its 8th or more firing without ever having annealed or turned the necks. I put this down to a low neck tension level but with some inconsistencies.

You said these were old stock/new cases . I doubt neck turning Lapua cases would show much improvement .
Regardless , the expander sets the final neck size and any out of the box inconsistencies were addressed by running the expander through them . I'm not saying they were 100% consistent.
In my opinion your results demonstrate the importance of consistency rather than the amount of neck tension .
Had you done a comparison of brass that you had set different levels of neck tension in , then I would say you'd demonstrated the difference between low and higher neck tension . As it is , out of the box cases , the degree of neck tension and consistency are an unknown .

 

[NullMac]

Depends on the expander ball. Some of them may give consistent neck tension but they also give you run out.

Running the necks over a mandrel is possibly a better bet. I have a rifle that shoots 0.2 and I don't do any of that. Don't sort cases or trim necks.

Bullets, barrel, bedding.

 

[Steff]

Did you chamfer your case necks?

Not enough neck tension causes ignition issues.

US DoD spent a lot of time and money researching and developing ammunition for their sniper rifle systems. Their findings were that a slight crimp was beneficial across the board.

Maybe they should have just asked @Muir...

I had thought of giving them a crimp instead of expanding the necks. I have the Lee FC dies lying around. But I decided against it. I had try crimping before on various loads and calibres and never found it to be beneficial, regardless of what Muir thinks.

And no, I did not chamfer the necks. No need to, they were clean and no shavings even on the first, tight bullet seatings.

 

[Steff]

Depends on the expander ball. Some of them may give consistent neck tension but they also give you run out.

Running the necks over a mandrel is possibly a better bet. I have a rifle that shoots 0.2 and I don't do any of that. Don't sort cases or trim necks.

Bullets, barrel, bedding.

Using a mandrel was my initial thought. But I don‘t have one. And thinking about it I couldn‘t see what the difference between a mandrel and an expander should be. They are both steel rods. The only difference is the length of the determining diameter part. So I saw no point in spending money on it even though I am the first to yes to good tools.

Anyway, it shoots into a 1/2“ now and I am happy.

 

[Jelen]

Until recently I have largely negated the influence of neck tension on accuracy. Party based on own experience ( I don‘t anneal) and also backed up by a test performed by Sead on the Accurate Reloading Forum.
I was right - and then again not.

The other week I brought 100 new Lapua .308 cases into operation which had been lying in my cupboard for 20 years. On seating the bullets for the test loads I noticed how tight the necks were. The test firing gave my quite severe vertical spreads, regardless of the charge weights. The trend was, 3 were perfect, 1 was 2“ low and one in between. Very unsatisfactory.

Remembering the tight bullet seating I ran the expander ball of my Redding neck sizing die without the bushing installed in and out of the rest of the yet unfired cases using some graphite.

Bingo, no more vertical spread. So my new theory is that high neck tension will indeed induce problems if it is not perfectly constant. On a lower level variations in neck tension have a negligible effect. A steep statement, but it reflects what I have seen so far.

Funny old thing. I recently bought a new box of Lapua brass for my 6.5x55 and experienced a much greater neck inconsistency than ever before. The tighter ones were a pig to get my expander into. I ended up with 3 batches of expanded cases, Tight, Medium and Loose necks. Wondering how this would affect velocity/ES I loaded 3 batches of a proven load (used in my old brass). Each batch of 3 cartridges was 1 x Tight, 1 x Medium, 1 x Loose neck. Fired at 100m over a Magneto V3 with a cooled barrel between each shot.
I was expecting some sort of predictable pattern, perhaps vertical stringing, or the tight necks producing a faster velocity, or better ES. What I got was:
Group1. ES 34 & 7/10th" group.
Group2. ES 17 & 1" group.
group3. ES 46 & 6/10th" group. So, not as consistent as my old load but, as said above, good enough for Roe deer out to 200m. But a 4" gong at 400m, well that's a different beast altogether.

 

[User00040]

What neck expander mandrels are you lot using?

Shoving an unsupported metal rod down the case neck won't do wonders for concentricity...

 

[MarinePMI]

What neck expander mandrels are you lot using?

Shoving an unsupported metal rod down the case neck won't do wonders for concentricity...

Sinclair. Not sure I'd agree with your concentricity statement, nor would a lot of BR shooters...besides, the Sinclair mandrel die has a fair amount of play to allow the mandrel to self-center before it backs into the cap on top of the die.

 

[jcampbellsmith]

Caliber Specific Expander Mandrel Kits

Our caliber specific expander mandrels are available in .0005” increments in calibers 22 to 338 and will range from .001” above bullet diameter to at least .003” below bullet diameter depending on caliber. This will allow the reloader to find proper neck tension to fine-tune their loads. The...

21stcenturyinnovation.com

Regards
JCS

 

[Jelen]

Caliber Specific Expander Mandrel Kits

Our caliber specific expander mandrels are available in .0005” increments in calibers 22 to 338 and will range from .001” above bullet diameter to at least .003” below bullet diameter depending on caliber. This will allow the reloader to find proper neck tension to fine-tune their loads. The...

21stcenturyinnovation.com

Regards
JCS

These will definitely do the job. However, at $278 (plus what HMRC will steal at this end) I think I'll stick with my Sinclair expander mandrel for the time being.

 

[Utectok]

I always expand new lapua cases as I find them tight especially in 6.5x55 flavours

 

[Bowland blades]

You said these were old stock/new cases . I doubt neck turning Lapua cases would show much improvement .
Regardless , the expander sets the final neck size and any out of the box inconsistencies were addressed by running the expander through them . I'm not saying they were 100% consistent.
In my opinion your results demonstrate the importance of consistency rather than the amount of neck tension .
Had you done a comparison of brass that you had set different levels of neck tension in , then I would say you'd demonstrated the difference between low and higher neck tension . As it is , out of the box cases , the degree of neck tension and consistency are an unknown .

Personally i experimented with neck turning when i competed . In a gun with a tight cut chamber specific for turning you pretty much have to but in a regular tight side of std you do not . The only difference turning made was on my time , it didn't show any better accuracy at ant range window out to 1,000 yards , indeed until i really understood how to do it best , it just wasted good brass. An absolute No Dont do this - regards hunting use
std high quality brass , no mixed batches and get bullet run out tested to 2 tho' or less via quality brass and good gear your all good
Indeed i Dont even check run out once i have set up what works for the individual rifle .

 

[ChesterP]

Of course neck tension matters. Not so much the amount but the consistency. Anything that affects pressures will affect MV and POI at distance. You may not see it at 100 yds but you most certainly will further out.