Neck turning experiment

[Davee]

I was finding what seemed to me to be odd groups, rifle in a led-sled would throw between 45mm and 16mm groups. The led-sled all but eliminates me as once setup it should not change significantly. Talking about this to a long range shooter, he invited me to bring some loaded rounds to him. Checked the neck concentricity, not too good: checked run out of bullet not good. As it is a 6.5x55 with a long neck, we hypothesized that the bullet might be leaving the case at an angle due to a) uneven net tension and b) concentricity, thus causing problems as the barrel attempted to make it concentric. Sorry I'm not phrasing this too well. Thus:-
I measured the wall thickness of a prepared case, varied from 0.33 mm to 0.37mm around the rim
Neck turned down to 0.34 mm to 0.33 mm, some cases virtually untouched, some trimmed one side and some all the way round.
Loaded 20 rounds with normal cases and 20 with neck turned, the later giving a more consistent pressure when sizing and bullet seating
Range results, much tighter 5 shot groups with the neck turned cases consistently less than 25mm, less muzzle flip, a crisper recoil and 100-125 fps increase in speed, up from 2780 to 2900, lower spread in muzzle velocity -ES still in the 20's. No pressure signs, but more even bolt pressure, both on closing and opening.
Now the questions
1) where did that speed increase come from? does it represent the loss of efficiency on not having to correct the bullet concentricity or is it neck tension? or a combination?
2) would I gain anything by necking to down to 0.33, and binning anything less?
3) what is the minimum neck thickness for 6.5x55 Skan, I can only find a maximum?
4) should I now get a bushing die instead of the normal RCBS one?

Cartridges, Lapua brass, annealed after 4 firings, CCI LR200 primers, 42gr +- .01gr -yes I do have a laboratory scale- of Viht 550, 129gr Gamekings, 100m range, essentially no wind, 23C.

I've changed something, so will go back and OCD the load, 2900 fps is above the upper edge of the previous plateau.

Any suggestions other than I'm a bit OTT, which I freely admit to!

 

[User00033]

That mate is a bloody interesting set of questions. Hopefully the experts will arrive, lots to learn.

 

[Yorric]

In response to Q1, Maybe thinner necks obturate quicker and seal the chamber better, giving less blowby pressure loss/variation & hence greater velocity.

Ian

 

[robus10T]

I found that neck turning gives more consistent neck tension thus giving better groupings and so does increase fps for some reason dont no why the only thing i can think on is that more consistent neck tension reduces the energy needed to push out the projectile. Thus an increase in fps and also noticed the fps has less of differance. Hope this helps. Also as far as im aware that as of thickness i think it is advised not to go below 12 thou

 

[Bavarianbrit]

Find some benchrest forum they will have all the info.

 

[NigelM]

I did quite a lot of work on neck turning and concentricity last year. My conclusions were as follows:

Neck turning: I was using good brass, Lapua, which varied on a Sinclair gauge between 14.5 thou and 15.5 thou. Not very much. When all turned down to 14.5 thou and shot again with no other changes to the load I could not measure any discernible difference in group sizes or ES. The conclusion was that if using good brass with little variation in wall thickness I wouldn't bother again.

Concentricity: My loads were varying between 1 thou of runout to about 8 thou measured half way between the tip and the ogive. I separated out into three batches, less than 2 thou, 2-5 thou and over 5 thou. There was a measurable difference of almost 1/2" in group sizes. Tried all sorts of things to reduce runout including turning the case twice whilst seating, rubber o-rings between the die and the press etc. Eventually changed to a VLD insert in the seating die which sorted the problem out. Conclusion was that this was far more important than neck turning if using good quality brass and looking for those consistent 1/2" groups.

Not a scientific study into the subject, but I hope that helps, although reading your OP again it doesn't seem to answer many of your questions!

 

[Laurie]

I did quite a lot of work on neck turning and concentricity last year. My conclusions were as follows:

Neck turning: I was using good brass, Lapua, which varied on a Sinclair gauge between 14.5 thou and 15.5 thou. Not very much. When all turned down to 14.5 thou and shot again with no other changes to the load I could not measure any discernible difference in group sizes or ES. The conclusion was that if using good brass with little variation in wall thickness I wouldn't bother again.

That's what I'd expect. Unless being used in a match quality rifle with either a custom neck section or 'minimum SAAMI' chamber, out of the box Lapua brass is normally consistent enough to use as is and turning will show little to no improvement.

There are two reasons for neck turning. One is case to chamber fit in 'tight neck' chambers. Take short distance BR 6PPC rifles as an example. Brass starts as Lapua 220 Russian necked up which has 12 to 13 thou' thick necks. The common chamber for a PPC BR job is 0.262". Subtract 3 thou' from that for clearance and you get a maximum case-neck 0.259" on a loaded round. With 13 thou neck thickness brass the round will measure 0.243" + 0.013" + 0.013" = 0.269", ie a full 10 thou' oversize - it won't even chamber in such a tight-neck chamber. Necks are turned down to traditionally 0.0085" to give a loaded round O/D of 0.260" a tiny 2 thou' overall clearance (one thou' at any point of the neck / chamber), but today the trend is to turn down another half and produce 3 thou' overall clearance.

In this case, it's not just about running with very close and consistent clearances, as it has been found that the round shoots better with very thin wall necks. In any event, many custom rifles / chambers need turned brass simply to fit and to be give enough clearnace to be fired safely. (Nil clearance or jam = super-high pressures = dangerous situation.)

For a 308 WIN or 223 Rem F/TR rifle built with a 'minimum SAAMI' chamber, the norm is to either use very high quality brass as is out of the box, or to give a small 'clean-up' neck turn. The latter makes every case the same in the chamber at the expense of a small increase in clearances.

Most out of the box sporting rifles come with chamber necks well above minimum SAAMI size. Brass turning simply increases already too large clearances, works the brass more and shows no benefits.

As always, you generally get what you pay for - buy Lapua, Norma, or RWS brass, and now the increasingly available Peterson Cartridge and unless you have a custom rifle built to out and out match rifle specifications, forget about any case-prepping tricks. You'll not improve on the out of the box cases if they're good, and more often than not get the extra cost back eventually through more firings before they go into the scrap box.

 

[deeangeo]

That's what I'd expect. Unless being used in a match quality rifle with either a custom neck section or 'minimum SAAMI' chamber, out of the box Lapua brass is normally consistent enough to use as is and turning will show little to no improvement.

There are two reasons for neck turning. One is case to chamber fit in 'tight neck' chambers. Take short distance BR 6PPC rifles as an example. Brass starts as Lapua 220 Russian necked up which has 12 to 13 thou' thick necks. The common chamber for a PPC BR job is 0.262". Subtract 3 thou' from that for clearance and you get a maximum case-neck 0.259" on a loaded round. With 13 thou neck thickness brass the round will measure 0.243" + 0.013" + 0.013" = 0.269", ie a full 10 thou' oversize - it won't even chamber in such a tight-neck chamber. Necks are turned down to traditionally 0.0085" to give a loaded round O/D of 0.260" a tiny 2 thou' overall clearance (one thou' at any point of the neck / chamber), but today the trend is to turn down another half and produce 3 thou' overall clearance.

In this case, it's not just about running with very close and consistent clearances, as it has been found that the round shoots better with very thin wall necks. In any event, many custom rifles / chambers need turned brass simply to fit and to be give enough clearnace to be fired safely. (Nil clearance or jam = super-high pressures = dangerous situation.)

For a 308 WIN or 223 Rem F/TR rifle built with a 'minimum SAAMI' chamber, the norm is to either use very high quality brass as is out of the box, or to give a small 'clean-up' neck turn. The latter makes every case the same in the chamber at the expense of a small increase in clearances.

Most out of the box sporting rifles come with chamber necks well above minimum SAAMI size. Brass turning simply increases already too large clearances, works the brass more and shows no benefits.

As always, you generally get what you pay for - buy Lapua, Norma, or RWS brass, and now the increasingly available Peterson Cartridge and unless you have a custom rifle built to out and out match rifle specifications, forget about any case-prepping tricks. You'll not improve on the out of the box cases if they're good, and more often than not get the extra cost back eventually through more firings before they go into the scrap box.

+1, agreed.

 

[NigelM]

That's what I'd expect. Unless being used in a match quality rifle with either a custom neck section or 'minimum SAAMI' chamber, out of the box Lapua brass is normally consistent enough to use as is and turning will show little to no improvement.

There are two reasons for neck turning. One is case to chamber fit in 'tight neck' chambers. Take short distance BR 6PPC rifles as an example. Brass starts as Lapua 220 Russian necked up which has 12 to 13 thou' thick necks. The common chamber for a PPC BR job is 0.262". Subtract 3 thou' from that for clearance and you get a maximum case-neck 0.259" on a loaded round. With 13 thou neck thickness brass the round will measure 0.243" + 0.013" + 0.013" = 0.269", ie a full 10 thou' oversize - it won't even chamber in such a tight-neck chamber. Necks are turned down to traditionally 0.0085" to give a loaded round O/D of 0.260" a tiny 2 thou' overall clearance (one thou' at any point of the neck / chamber), but today the trend is to turn down another half and produce 3 thou' overall clearance.

In this case, it's not just about running with very close and consistent clearances, as it has been found that the round shoots better with very thin wall necks. In any event, many custom rifles / chambers need turned brass simply to fit and to be give enough clearnace to be fired safely. (Nil clearance or jam = super-high pressures = dangerous situation.)

For a 308 WIN or 223 Rem F/TR rifle built with a 'minimum SAAMI' chamber, the norm is to either use very high quality brass as is out of the box, or to give a small 'clean-up' neck turn. The latter makes every case the same in the chamber at the expense of a small increase in clearances.

Most out of the box sporting rifles come with chamber necks well above minimum SAAMI size. Brass turning simply increases already too large clearances, works the brass more and shows no benefits.

As always, you generally get what you pay for - buy Lapua, Norma, or RWS brass, and now the increasingly available Peterson Cartridge and unless you have a custom rifle built to out and out match rifle specifications, forget about any case-prepping tricks. You'll not improve on the out of the box cases if they're good, and more often than not get the extra cost back eventually through more firings before they go into the scrap box.

Thank you Laurie. I learnt a lot through the exercise. Some things worked, like the concentricity and more accurate powder measurement, some things didn't, like neck turning. I'm now very happy with where I am on the whole process and believe I'm getting the best out my reloading.

Good to have my findings endorsed by someone who know's what he's talking about!

 

[deeangeo]

I did quite a lot of work on neck turning and concentricity last year. My conclusions were as follows:

Neck turning: I was using good brass, Lapua, which varied on a Sinclair gauge between 14.5 thou and 15.5 thou. Not very much. When all turned down to 14.5 thou and shot again with no other changes to the load I could not measure any discernible difference in group sizes or ES. The conclusion was that if using good brass with little variation in wall thickness I wouldn't bother again.

Concentricity: My loads were varying between 1 thou of runout to about 8 thou measured half way between the tip and the ogive. I separated out into three batches, less than 2 thou, 2-5 thou and over 5 thou. There was a measurable difference of almost 1/2" in group sizes. Tried all sorts of things to reduce runout including turning the case twice whilst seating, rubber o-rings between the die and the press etc. Eventually changed to a VLD insert in the seating die which sorted the problem out. Conclusion was that this was far more important than neck turning if using good quality brass and looking for those consistent 1/2" groups.

Not a scientific study into the subject, but I hope that helps, although reading your OP again it doesn't seem to answer many of your questions!

For interest, I do use an O ring between RCBS F/L die and press and with the decap rod backed right in then centralised, I find with most usual brands of cases, around .0005” case neck/body run out, rarely more.

Low run out when Bullet seating however, is in my experience, much harder to achieve, even with good competition seating dies and to eventually achieve the best consistency I could, I bought an arbor press and LE Wilson seating dies.
The resulting difference is I now achieve an average bullet/case max run out of .0025” occasionally a liitle more, but almost never greater than .004”.
However, right or wrong I measure bullet run out at the top of the ogive, (close to bullet shank) rather than halfway between bullet tip and top of ogive. I measure at that point because my thinking is, thats the point that needs to evenly engage the rifling.

Does this all make much difference for stalking purposes? Absolutely not, certainly not at usual ranges for taking quarry.
I do what I do because I can and probably I’m fussy too.
I’m also older and need all the help I can get.

I’m certain if shooting competition it would make some difference, especially at longer ranges.

 

[NigelM]

For interest, I do use an O ring between RCBS F/L die and press and with the decap rod backed right in then centralised, I find with most usual brands of cases, around .0005” case neck/body run out, rarely more.

Low run out when Bullet seating however, is in my experience, much harder to achieve, even with good competition seating dies and to eventually achieve the best consistency I could, I bought an arbor press and LE Wilson seating dies.
The resulting difference is I now achieve an average bullet/case max run out of .0025” occasionally a liitle more, but almost never greater than .004”.
However, right or wrong I measure bullet run out at the top of the ogive, (close to bullet shank) rather than halfway between bullet tip and top of ogive. I measure at that point because my thinking is, thats the point that needs to evenly engage the rifling.

Does this all make much difference for stalking purposes? Absolutely not, certainly not at usual ranges for taking quarry.
I do what I do because I can and probably I’m fussy too.
I’m also older and need all the help I can get.

I’m certain if shooting competition it would make some difference, especially at longer ranges.

Interesting how we all do it a little differently. My measurement half way between the tip and the ogive is because if there is a concentricity issue it is more exaggerated at that point and so easier to see. I know I'm making life more difficult for myself but if OCD enough to be looking for perfection then why not make it a bit more challenging!

I run the Wilson seating dies on the 22BR and agree they are excellent. Just can't bring myself to invest in them for all the other chamberings to replace what I have already got.

And agreed it makes no difference at UK stalking ranges, I just enjoy an accurate rifle that shoots little groups. Part of the hobby from my perspective.

 

[deeangeo]

Interesting how we all do it a little differently. My measurement half way between the tip and the ogive is because if there is a concentricity issue it is more exaggerated at that point and so easier to see. I know I'm making life more difficult for myself but if OCD enough to be looking for perfection then why not make it a bit more challenging!

I run the Wilson seating dies on the 22BR and agree they are excellent. Just can't bring myself to invest in them for all the other chamberings to replace what I have already got.

And agreed it makes no difference at UK stalking ranges, I just enjoy an accurate rifle that shoots little groups. Part of the hobby from my perspective.

It is a valid point you make NigelM on the exaggerated aspect of run out where you measure and the 'additional challenge' it presents.

My take on it though is, e.g. when I measure the case neck and find the small .0005" run out present after F/L sizing cases, I presume that to not be an issue with the die, but rather a slight variable thickness of/on the outside case neck brass.

I have just for interest measured bullets for run out on the shank, these being Sierra Prohunter, SST & Accubond and found run out on all makes.
It's only small variation not exceeding .001" that I have measured.
So, I presume that also to be copper thickness variation while being extruded and bullet manufactured.

Personally as said, it matters not a bit for hunting and I'm sure the long range and bench rest boys have their own means of 'perfecting' their reloads but likely at lengths and regime that I'm happy to stay away from.
Including outside neck turning.
I cannot comment on bushing dies though as I have never used any.

As far as I'm concerned, my own case prep regime, likely as yours, is well routined and managed to our satisfaction.

 

[Davee]

Thanks to all who contributed. To clarify a couple of points, I'm not into bench rest or shooting competitions in general, nor am I interested in long range hunting - mainly because of lack of experience and opportunity-where I live the longest range I can safely zero at with my current permissions is a tad over 120 metres- to shoot at longer distances I would have to put up high seats that would require planning permission - it's as flat as a pancake around here! And yes the accuracy is ok for stalking. I am merely annoyed at the variability that I'm getting. The 6.5x55 has a long throat and there is no way that I can get 20 thou off the lands, so concentricity and neck tension variables are the only things left that I can reasonably improve upon, and neck turning has only to be done once, where as bullet tuning has to be done for every shot, -that is ok for the bench rest guys, in fact I think they derive as much satisfaction from preparing their ammunition as shooting it. If the clearance was excessive I would have expected to see smoky cases, I didn't, which together with the increase in muzzle velocity suggests that it isn't.
I have sat and measured the wall thicknesses of a new box of Lapua cases and found that the minimum wall thickness is 0.013 inches, the thickest was .0154.
So in addition to making up rounds for the ladder test I'm also making some at 13 thou to see if that changes anything.

 

[Border]

Hi Davee. Are you FL sizing the brass? I was always under the impression that neck turning for rifles without tight necks was a waste of time. Regarding the deadsled, I am not entirely sure that that will take out the entire human equasion. Maybe if the action was bolted to an rsj as per factory testing and fired remotely?
It may be that your load may still benefit from further tuning or a change of projectile/powder, not sure I have heard of 129 SGK? Your results may also be a bedding anamoly? The Swede can be very accurate and doesnt need to have lands chased to achieve very good accuracy. Enough bullet hold is important to aid obturation and avoid sooty cases. Good luck on your further reloading adventures........

 

[Muir]

I don't neck turn unless I am in that situation where I'm reforming a case into another and the resulting neck is too thick. Then I will neck turn brass only if I cannot neck ream which I believe to be superior -though more difficult.

To the OP. In a factory chamber you are wasting your time trying to shave .002" off of a new case. Neither your rifle, nor your loading gear is up to the task of delivering any noticeable difference in accuracy by doing this. Not being harsh or demeaning, just relating what I've learned over the years.~Muir

 

[Selous]

What is the runout of the neck on a fired case , ie how concentric is the chamber?

 

[Muir]

More measuring! That's what's needed!
If it is a decent rifle in 6.5x55 and groups are running fro 16mm to 45mm it isn't the rifle and probably not the brass. I have military Swedish Mausers that are more consistent than that with PPU factory ammo. ~Muir

 

[awmc]

I used to neck turn quite a bit

Blondes mostly

Can’t afford it now

 

[Davee]

As previously stated I am not into competitive target shooting, but merely annoyed by 'flyers', yes some were my fault, others you get the 'what the hell happened there thought'. So according to German A Salazar " I'm not talking about a theoretical improvement, but a real one, an improvement that lies in equalizing and optimizing the neck tension of your loaded rounds. Inconsistent neck tension is a real contributor to increased muzzle velocity variance which itself is a significant factor in increased elevation dispersion at long range. So there's our basic reason for neck turning: to equalize and optimize neck tension in order to reduce elevation dispersion." That seems to me to be a valid reason to try it!

So 20 rounds out of the box cases, 20 turned to 0.34 mm neck and 20 to 0.33mm neck. Fired in groups of 5, two minutes between shots, 5 minutes between each group.I got the following.
..........fps.....ES......SD .....smallest group
oftb .2779 ...62 ....22.56 .....21.2 mm
0.34 2836 ...42.....18.18.......14.8
0.33 2852 ...22.......6.58....... 9.2

All of the above except group size is for all 20 shots, I know not enough to be totally valid for statistical purposes, but they indicate a positive trend. All 'flyers' included in these results. And yes all 60 would have grounded a deer.

What have I got out of it:-
Satisfaction.

Thanks to all