Neck turning with a wobbly drill

[Geezedtee]

Hi.

I've just re-read the post about neck turning, particularly the German Salazar article.

At the time that the post was put up i asked "It mentions a wobbly drill, but it doesn't say whether a wobbly drill does a bad neck turn? I'm assuming the mandrel in the neck keeps everything aligned so the cut is true?" I never got an answer.

I'm asking again because I've just tried it on Lapua brass. As I was adjusting the cutter the first cut only cleaned 50% of the neck on one side. I've always believed Lapua brass was the most consistent. So is the brass not as consistent as people say, or is the wobbly drill the cause?

I've attached a photo (I know I cut it too quickly). Any help would be greatly appreciated.

[Popsbengo]

It looks like you've skimmed a thou or two, it wouldn't be a surprise that the outside of the neck varied that amount wrt to the inside.  Any vibration in cutting is to be avoided so a wobbly drill sounds like a problem, of course this is moderated by a tight fitting mandrel holding the tool alignment  - a sloppy mandrel and your going to have problems.

You may improve the wobble by thoroughly cleaning the chuck and carefully tightening so as to ensure self-centring of the jaws is as good as you can get.

[Laurie]

Like everybody else, Lapua consistency does vary between case types and  also production lots. In general, it's very good though - but if by 'good' you think you're going to get nil variation around each individual case's neck walls, you'll be disappointed. Here are readings from a 25 strong sample of new Lapua 223 Rem Match brass bought earlier this year (Lot LPT00241) taken with a Sinclair's Starrett ball mike on a small stand combo. Each case neck is measured at three points around its circumference and recorded. So, 75 readings overall.

 

Overall measurement range (ie over all 75 readings): 0.0124 - 0.0134" = 0.001"

Range within individual cases between lowest and highest of the three measurements: 19 ex 25 equal to or less than 0.0005"; the remaining six pieces 0.0006 - 0.0009" variance.

Best individual case consistency: one case with nil variance over the three readings (0.0129")

Worst: 0.0009" (0.0124 - 0.0129" which also happen to be the lowest and highest individual readings of the 75).

 

I consider these results extremely good. (Measure PPU the same way if you want a contrast.) Nevertheless, with the neck-turner cutter set to just contact high spots, you'll naturally get some cases with a limited area actually cut.

 

Yes, the mandrel should in theory keep the case in continuous and perfect alignment with the cutter blade, but in real life it'll struggle to do so to give nil variation in cut. A great deal depends on case-neck to mandrel match - both too loose and too tight give poor results. Also, the lube used and consistency of its application are important.  

  

 

 

[Geezedtee]

Many thanks for your replies. Reading your  answers I suspect it may be a combination of varying neck thickness (thank you Laurie) and a neck tension issue. The K&M expander gives me snug fit but maybe too loose.

I'll clean the drill chuck - or even invest in a better drill and try again.

[Popsbengo]

14 minutes ago, Geezedtee said:

Many thanks for your replies. Reading your  answers I suspect it may be a combination of varying neck thickness (thank you Laurie) and a neck tension issue. The K&M expander gives me snug fit but maybe too loose.

I'll clean the drill chuck - or even invest in a better drill and try again.

It's very hard to get perfect alignment with any three jaw chuck.  On a lathe a collet chuck works perfectly with a clean machined part (well almost).  I don't know if there's a collet drill chuck available however routers use a collet chuck to grip the tool shank (because the tool needs to be reliably centred without wobble)

[Geezedtee]

OK. I'm just trying to clean up the necks to get a tad more consistency at this stage, not go  for a full neck turn.

I've just used my K&M expander mandrel on 3 new and 3 once fired neck sized Lapua cases. The cases now easily slide onto the K&M Neck Turner pilot and I can feel a bit of play by hand, certainly don't need any lube that's for sure.

I'm thinking that maybe just leaving the necks unturned might be better than than using a loose fitting pilot?

[Popsbengo]

8 minutes ago, Geezedtee said:

OK. I'm just trying to clean up the necks to get a tad more consistency at this stage, not go  for a full neck turn.

I've just used my K&M expander mandrel on 3 new and 3 once fired neck sized Lapua cases. The cases now easily slide onto the K&M Neck Turner pilot and I can feel a bit of play by hand, certainly don't need any lube that's for sure.

I'm thinking that maybe just leaving the necks unturned might be better than than using a loose fitting pilot?

I would not turn the necks unless you have a chamber that requires that.  Lapua brass is excellent with just some minor adjustments - I found virgin out of the box shoulder to head lengths to be a bit variable and neck length too.  I load and shoot the brass, F/L size around 2thou knock back of the shoulders and trim the length of the neck to be consistent - find the shortest case and trim to that (If it's good new brass the shortest will still be well inside the spec).  That's now a set of matched brass cases.  Of course, I still need to measure after firing and adjust over time.

The inside of the neck is what positions the bullet axially so a mandrel could be used to adjust that after bushing the neck down  - if it's really necessary after checking run-out.

[Laurie]

2 hours ago, Geezedtee said:

certainly don't need any lube that's for sure.

 

Lube is essential in this operation, and so essential that relubing the turner mandrel between cases is the norm, at least with standard steel versions - can't comment on the much more expensive carbide examples. With ordinary steel mandrels and a proper case-fit, the mandrel slowly heats up over a series of cases being turned even when a high quality lube is applied, and the results quickly go badly downhill, not to mention the strain on a hand-held drill and its chuck + case-holder, and how many cases you can do before the battery charge runs down. Try to do it without lube and you might end up with a case seized onto the mandrel at least temporarily until the mandrel cools and contracts. (I like small low-voltage cheapo drills for this job, but charge life is limited - too tight a case on the mandrel / excessive friction and the charge quickly runs out. Not only does the number of cases turned in each batch between charges drop dramatically, but chuck revs drop too, so you quickly build an inconsistent practice into the operation.) That's where people who do their turning on a lathe have a big plus - not only quicker and easier, but constant case-neck speed under the cutter throughout.

I partially agree with @Popsbengoabout the need for neck-turning in the first place. If you're talking factory rifle, forget it - you may in fact do more harm than good than using brass out of the box as supplied by increasing already over-large neck to chamber clearances. The one exception may be if you've reformed an already thick-wall larger-calibre case by necking it down as this thickens the neck walls. (Even here, most factory chambers have so much clearance, that you'd be unlikely/unlucky to get into trouble.)

When you get gunsmith built / rebarrelled rifles with 'minimum-SAAMI' chambers as is the norm in F-Class and good varmint rifles, a very light 'clean-up' turn isn't necessary in most cases, but usually won't do any harm and might make a small but useful improvement. A good example is 6mmBR with a custom 'no-turn' chamber optimised for one make of brass, normally Lapua. (There was hell to pay when Lapua moved from the cardboard 'gold' cartons to the 'blue box' packaging some years ago as it reduced the 6BR neck thickness by a thou' or more at the same time. This increased neck to chamber clearance by two or three thou' in 'no-turn' chambers.) If you have a good batch of brass, and/or do a neck-thickness selection sort, you literally can use brass out of the box. Many shooters though do the small clean-up turn nevertheless to be happy they have removed yet another potential inconsistency.

I have an interesting exercise in mind in this field. I normally use Lapua 6.5 Grendel brass, and it really is good - amongst the best I've measured in any cartridge and over more than one production lot. I also have 100 PPU Grendel cases where case neck thickness variations range from a single case with nil to one with three thou'.  There is also a very large weight range for such a small case, but I decided to do a sort on neck thickness rather than weight to see if I can spot any difference on the range in a factory rifle between the 25 best cases and the 25 worst. The second question is, that assuming the more consistent batch does give some benefits in practice, what effect does improving neck consistency through turning have on the 'bad bunch', in particular the three thou' variation around the neck example. My interest in this example is that large neck thickness variations often don't just affect the neck, but the variations carry on down the case body, and in fact can get worse as you move along. Both ammunition factories and experimenters like Creighton Audette proved a long time ago that 3-thou' case body wall variations are key boundary in ammunition consistency - pass that discrepancy and you get into the 'banana case syndrome' where the case bends in the chamber under peak pressures. Audette marked the thick or thin sides of such cases on the case-head and depending on how he chambered the rounds could at one extreme produce a decent group, or at the other, near every shot a flier. Moreover, he could predict the direction the flier would take too depending on where he placed the index marks on chambering the resulting cartridges. This was back in the days when 30-30WCF and 30-06 Springfield were the American norm, ie long body designs, so the stubby, heavily built Grendel may be much more resistant to wall inconsistencies.

[Geezedtee]

Thank you. I'm glad I asked the question as your answers have supported my initial doubts.

Pops. That is what I do with my Lapua brass prep too.

Laurie.  I do lube my .243 when neck turning and a 'clean up' does make a small improvement. I didn't use the correct terminology in my post re 'wobble'. What I should have said is that the expanded case easily fits and spins on the pilot by using my finger tips without any lube applied to either case or pilot. That's how I felt the play on the pilot - something that didn't occur with my .243.  

Too much time on my hands and an idle 6.5 neck turner at the back of the drawer led me down the "path to perfection". I have returned the offending part to the back of the drawer.

Any one want a K&M 6.5 neck turner 🙄