NECK CLERANCE - IS IT IMPORTANT?

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Tim L
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Re: NECK CLERANCE - IS IT IMPORTANT?

#16 Postby Tim L » Fri Mar 15, 2019 8:52 am

wsftr wrote:
IMO you can have brass that has an uneven neck and still be concentric to the bore, you can have even necks and a bullet that isn't concentric to the bore

Agreed, but
Can the projectile be concentric with unturned brass that is sized in a bushing die?
If the neck is uneven and it is sized from the outside, won't that put the inside off centre?
Or
Are we saying that neck clearnce means neck wall variation is irrelevent because it doesnt touch anything and the brass is actually centered from the case wall?
Or
Are both contentions irrelevant and concentricity is actually achieved buy having suitable clearence in both with freebore centralising the bullet?

Gyro
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Re: NECK CLERANCE - IS IT IMPORTANT?

#17 Postby Gyro » Fri Mar 15, 2019 10:07 am

But lads there are actually ways you can have the loaded rounds bullet sitting right in line with the bore centre line. It's a whole lot of shagging around to get there and you need the skills and equipment, but it can be done.

Benchrest shooters have run "fitted necks" whereby the neck clearance is very fine. The bullet is only just gripped in the case neck and on firing there's only a fraction of room for the neck to expand. That neck clearance is so small that on firing the case neck does not get stretched beyond its elastic limit, so it keeps the same size after being fired and on reloading the case the next bullet is just pushed into the case with thumb pressure. And the case body is not sized either : the theory is that this will keep the case body totally filling the chamber and will therefore not allow the case to 'cock over' and upset that perfect place the bullet is supposedly located at. Maybe skip the fitted neck, but make sure the necks are perfect, and just neck size only ?

There are still some shooters who reckon the neck-size-only option is beneficial for the above reasons, They're the ones ya see fighting with their bolt handle .....

pjifl
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Re: NECK CLERANCE - IS IT IMPORTANT?

#18 Postby pjifl » Fri Mar 15, 2019 12:05 pm

Yes - some short range BR shooters use a neck clearance such that one never needs a die when reloading.

Just remember, however, that

1/ At short range, velocity variation if far less important.

2/ Many are proud of the fact that they only need a dozen extremely select cases at a competition and reload during relays. If we drive 2000 miles for a multiple event we need at least 200 loaded rounds or loading and weighing facilities.

3/ If for some reason they have a stuck case, usually they do not need to wait for a RO to solve the problem. Stuck cases and cleaning rods are almost expected on some SSAA benches. Hammers at benches also seem more acceptable !

BTW - I once saw a rifle shot using a cleaning rod as projectile .......


Peter Smith.

Gyro
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Re: NECK CLERANCE - IS IT IMPORTANT?

#19 Postby Gyro » Fri Mar 15, 2019 12:14 pm

pjifl wrote:Yes - some short range BR shooters use a neck clearance such that one never needs a die when reloading.

Just remember, however, that

1/ At short range, velocity variation if far less important.

2/ Many are proud of the fact that they only need a dozen extremely select cases at a competition and reload during relays. If we drive 2000 miles for a multiple event we need at least 200 loaded rounds or loading and weighing facilities.

3/ If for some reason they have a stuck case, usually they do not need to wait for a RO to solve the problem. Stuck cases and cleaning rods are almost expected on some SSAA benches. Hammers at benches also seem more acceptable !

BTW - I once saw a rifle shot using a cleaning rod as projectile .......


Peter Smith.


To be sure to be sure !!!

MAYBE the above story is right for the short range BR guys but for a bunch of practical reasons I'd say don't even think about it for an F Class rifle.

bruce moulds
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Re: NECK CLERANCE - IS IT IMPORTANT?

#20 Postby bruce moulds » Fri Mar 15, 2019 12:18 pm

cleaning rod for a projectile.
what would be the fineness ratio of that projectile?
long range muzzle loaders used a rod guide that stuck up into the line of sight in order to avoid such issues.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

John T
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Re: NECK CLERANCE - IS IT IMPORTANT?

#21 Postby John T » Fri Mar 15, 2019 3:53 pm

Keith, and no doubt proud of it.

Pete, thanks for the best explanation of why NOT to have a very fine clearance, that I have heard.

Let's agree that a 0.001 is out, but 0.002 is viable. Is a 0.002 clearance more consistent than a 0.004? What do the turners have to say?

If you look at the SAAMI drawings of the 7mm REM SAUM, they show the maximum case neck of 0.3200 and the minimum chamber neck of 0.3210. Not sure what conclusion, if any, can be drawn.

A buffalo boy might decide that if 0.320 is the largest neck he will ever buy, his reamer will have a 0.324 neck. If some makes are only 0.315, that's OK because a large clearance does not matter (keeping the different sizes batched, of course).

Regards,
John T.
15.3.19

Gyro
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Re: NECK CLERANCE - IS IT IMPORTANT?

#22 Postby Gyro » Fri Mar 15, 2019 5:15 pm

John T wrote:Keith, and no doubt proud of it.

Pete, thanks for the best explanation of why NOT to have a very fine clearance, that I have heard.

Let's agree that a 0.001 is out, but 0.002 is viable. Is a 0.002 clearance more consistent than a 0.004? What do the turners have to say?

If you look at the SAAMI drawings of the 7mm REM SAUM, they show the maximum case neck of 0.3200 and the minimum chamber neck of 0.3210. Not sure what conclusion, if any, can be drawn.

A buffalo boy might decide that if 0.320 is the largest neck he will ever buy, his reamer will have a 0.324 neck. If some makes are only 0.315, that's OK because a large clearance does not matter (keeping the different sizes batched, of course).

Regards,
John T.
15.3.19


I would suggest 0.002" ( .001/side ) is NOT viable John for the Joe Average neck turner. I mean "not viable" because the inevitable measuring errors by the "Layman", and case wall changes after a few firings could bite you.

You need a LOT of experience and understanding to be able to get away with running small neck clearances. And it seems it doesn't matter anyway as plenty of shooters are proving.

Go 0.004" ( .002/side ) minimum.

And get a GOOD BRAND BALL MICROMETER to measure with. And don't kid yourself that you have prepared good consistent necks until u have thoroughly measured them.

All the top shooters have ticked this box. Ya have to !!!!!!

Then focus on all the other things that compromise accuracy !!!!!!!!!!!! Grrrrrrrrrrrrrrr ......

Regards Saint Rob, the measurement snob.

pjifl
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Re: NECK CLERANCE - IS IT IMPORTANT?

#23 Postby pjifl » Fri Mar 15, 2019 6:33 pm

Just for completeness, I will mention that a very light skim is actually harder than a definite neck turning job.
An interrupted cut on Cartridge Brass is difficult to do and control well.

For anyone who has not done this, make sure that you have a very rigid setup, a razor sharp tool, and realize that it will develop a dull edge fairly quickly.

Often the material does not cut at all well. The tool edge skids instead of cutting. Then as you increase the feed or adjust the tool geometry it dives in and cuts too deep.

There are many traps for the newcomer who thinks it is simple.

Peter Smith.

bruce moulds
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Re: NECK CLERANCE - IS IT IMPORTANT?

#24 Postby bruce moulds » Fri Mar 15, 2019 7:32 pm

have you ever set a vernier or micrometer on 0.001 and looked at the gap?
this much per side is very little.
0.002 is not much more, but seems to work.
as we shoot a string, or more, how much crud can enter this clearance area of the chamber?
there will come a clearance where inconsistencies in this clearance become irrelevant.
shooting black powder cartridges, one way to achieve accuracy is to have a chamber where a bullet of 0.001 over groove diameter is a friction fit in a fired case, and the same in freebore if any.
bullets with grease grooves release freely in this situation, bumping up to fill the case when it obturates prior to moving.
unlubed paper patch bullets also release .
muzzle velocities are extremely consistent, often being as low as 4 to 5 fps EXTREME SPREAD for 10 shots.
why this is different for jacketed bullets and smokeless powder is hard to understand, but it is.
possibly the lead alloy bullets bumping up make a perfect seal immediately as opposed to the jacketed bullet possibly having a small amount of windage at the start of movement?
another way that accuracy is helped with a bpcr is to seat a bore diameter paper patched bullet into the rifling with a little friction.
this offers absolute alignment of bullet axis with bore axis, as long as all rifling grooves are evenly deep.
of course the lead bullet bumps into the rifling when you light the fire, but a jacketed bullet with smokeless cannot do this.
I have often wondered about swaging dual diameter jacketed bullets, where the front majority of the bearing surface is bore diameter such that it has a very slight friction fit when chambered.
the rest, rear, of the bearing surface would be groove diameter, and fit the case neck sized, and freebore if any.
the angle between the 2 diameters couls equal the leade/throat angle.
such a bullet would be absolutely aligned when chambered..
am now too old, too tired, and too poor to try it.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

bruce moulds
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Re: NECK CLERANCE - IS IT IMPORTANT?

#25 Postby bruce moulds » Fri Mar 15, 2019 7:41 pm

pete,
your last post makes good points.
normal neck turning tool cutters DO go blunt quite quickly.
standard tools might have to be adjusted several times in 50 cases, which already leaves room for doubt.
carbide ones are better.
a better turn is often achieved by doing at least 2 passes.
1st pass takes off the high spots and a bit more, and 2nd will then be much more even thickness.
a 3rd very thin one might be even better.
i would suggest that while a ball mike is necessary, it still pays to seat a bullet of known diameter, and measure the neck o.d. as a check.
incidentally I have found Winchester brass to cut more freely and cleanly than lapua, which looks torn more than cut in comparison.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

Matt P
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Re: NECK CLERANCE - IS IT IMPORTANT?

#26 Postby Matt P » Fri Mar 15, 2019 7:51 pm

Most people struggle to drive measuring equipment correctly, and then want to run very small clearances. Doesn't normally end well !
In most cases more clearance is better.
Matt P

wsftr
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Re: NECK CLERANCE - IS IT IMPORTANT?

#27 Postby wsftr » Sat Mar 16, 2019 10:56 am

Tim L wrote:
wsftr wrote:
IMO you can have brass that has an uneven neck and still be concentric to the bore, you can have even necks and a bullet that isn't concentric to the bore

Agreed, but
Can the projectile be concentric with unturned brass that is sized in a bushing die?
If the neck is uneven and it is sized from the outside, won't that put the inside off centre?
Or
Are we saying that neck clearnce means neck wall variation is irrelevent because it doesnt touch anything and the brass is actually centered from the case wall?
Or
Are both contentions irrelevant and concentricity is actually achieved buy having suitable clearence in both with freebore centralising the bullet?


mmm TBH we are talking different things.

Concentricity is one subject and clearance is another with neck thickness consistency another. There is a relationship between all 3 though.

IMO how even neck walls are relates to the way the neck releases the bullet...as does the overall thickness of the walls. As mentioned you can have very consistent neck thickness and still the neck is not concentric with the case. I bet most turn necks and measure necks with a ball micrometer. This does not measure concentricity.

There is a relationship between all 3 in that the case neck expands to seal against the chamber wall. The way it does this affects precision. A significantly uneven neck would touch the chamber at different timing/points and thus could affect precision. So even necks is best....but how uneven do they have to be before you can see a difference on paper? I would suggest that for many (buffalo boys) <.015" gets swallowed up in the noise. Noise being at least .5moa vertical at 1k.

From a precision point of view (ease of use is another topic) clearance relates to time. The time it takes for the neck to expand to seal. This time is also affected by the thickness of the neck. The thickness of the neck will also impact how much pressure is built before movement occurs by either the neck or bullet. I expect this time will affect harmonics and pressure and gas shape stuff like that. Anecdotally it appears that calibers such as .308 and 7mm prefer thicker necks and more time before seal takes place. I wouldn't be surprised if there was another combination of neck thickness and clearance that produced the same level of precision though...more - why would you bother KISS.

Concentricity is an interesting subject as there are various tools out there that measure it. Some methods are good at detecting all forms of concenticity others not so much. I don't have the articles at hand that discuss this suffice to say that using a common tool to measure bullet run out I can't see a difference on paper where run out is < .002".

For runout on my turned vs unturned brass I still ended up with run out of <.002" and no difference on paper. This simply told me the tolerance of modern good brass was within the tolerances of my other reloading practices such as bullet seating and not a significant contributor to be improved upon within my precision requirements on paper.

Yes theoretically an uneven neck sized from the outside pushes that uneveness to the inside (why do we outside neck size anyways ;) ).
But then we get a big lump of lead and copper and force the neck to expand out again.....hmmm what is actually going on with respect to concentricity...

All in all even necks are best. Concentric loads are best. The question for most shooters is - at what measurement of tolerance do I notice a difference.

bruce moulds
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Re: NECK CLERANCE - IS IT IMPORTANT?

#28 Postby bruce moulds » Sat Mar 16, 2019 12:32 pm

wsftr,
in all honesty, I have to ask whether I have ever been able to get ALL my bullets into 1/2 moa.
the biggest factors seem to be powder charge and seating depth, or at least bullet relation to the lands, not sure which.
and to some slight degree primers.
to keep down at 1/2 moa the gun and ammo have to be kept in tune with each other all the time.
neck turning makes a higher level of concentricity possible, and allows for a more constant neck grip.
necks should go over an expander prior to neck turning so that the lumps and bumps are on the outside to be cut off.
your point about harmonics caused by differing neck thicknesses is worthy of thought.
an experiment marking cases that produced fliers, and seeing if it happened next firing proved that throwing those cases away was a waste of time and brass.
an experiment indexing cases was also a waste of time.
moderate runout has not proven to be an impediment to my shooting.
maybe my tolerances need to tighten up a lot to get the accuracy some guys claim to get consistently.
maybe some of those fliers are technique induced, and some bending light or other conditions.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

wsftr
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Re: NECK CLERANCE - IS IT IMPORTANT?

#29 Postby wsftr » Sat Mar 16, 2019 1:20 pm

Hey Bruce - yip .5 moa vertical all of the time is a challenge...you can have a great tune in summer but no so much in cooler months. IMO thats not related to neck thickness or clearance.
My point is I have achieved that and better often enough to be on the mound at any given time and expect that outcome. I have had to change my setup to achieve that expectation too....
ETs and lab radars allow you to build an enormous set of data in real conditions over large time frames (years)...combined with measurements in the reloading room you can make informed choices even if the science isn't fully understood.
Seating depth - yip IMO that makes or breaks a load and that is where I put my effort and don't drink beer ;)
Personally I struggle with the whole grip concept - as far as I can tell we can only measure friction. Personally I think the aim is to achieve consistent release/neck expansion and alter the time that something occurs through either thicker or thinner neck walls.
IMO tight clearances are about working thin necks less and altering the time to seal.

Anything not being the same or consistent in some way has the potential to affect the result on paper - my stance would be very different if i was trying to shoot a 1.5" group at 1000 which is what I think some of the 1k BR boys are doing (I don't know if they are buffalo boys or not ;) ) Its just been my experience that I can shoot .5moa and at times .4moa frequently in matches (not necessarily executing best shot because I want to get that shot away before the wind changes) without neck turning so IMO neck turning is something that starts to assist inside those numbers. The assumption being - good quality brass is used.
YMMV

John T
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Re: NECK CLERANCE - IS IT IMPORTANT?

#30 Postby John T » Sat Mar 16, 2019 8:38 pm

Buffalo Boys.

what are your chamber necks for any 7mm?


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