HANDLOADING: SOMEWHERE TO TURN
Created on 14th May 2009
Continuing his study of case necks, LAURIE HOLLAND takes a look at turning as a way to improve performance
LAST MONTH I took a look at measuring case necks using 25-piece samples of new Lapua and Remington .308 Winchester cases. The summary results table is included again for clarity, and you'll note that just over two-thirds of the Lapua sample, 17 cases, had less than a thousandth of an inch (0.001") variation measured at three points. This is a good result, but how much difference was there between cases? 15 of the 17 were on or close to 0.016" (16 thou) and the other two were thicker at 0.017", so it wouldn't be difficult to take a couple of hundred cases and batch them. The Remingtons produced a smaller individual thickest value compared to the same 16 thou norm, with nothing exceeding 0.017". More produced a one to one and a half thou individual variation, most such within 0.015-0.0165". I decided to give all 200 cases a light neck-turn, cutting everything above 0.0155". This removed metal from around the entire neck of some, but more often only touched part of it. The largest individual remaining variation was a half-thou at 0.015 to 0.0155" after turning. Why not set the tool to 15 thou and reduce everything to that thickness? The object of this exercise was to remove as little metal as possible and, in the rifle these cases were for, a half-thou is neither here nor there.
This task was a good excuse to try Sinclair International's new NT4000 neck-turner. These tools come in various forms, but hand-held U-form models are the most commonly used by precision handloaders. Some of the larger reloading tool companies still offer cylindrical models as an attachment for their case trimmers, but these give poorer results. We now have Hornady, Forster and RCBS joining the specialist suppliers with these apparently simple precision hand-tools. I described it as ‘U-form', but a mandrel is an essential addition to support the case-neck while turning is under way, and this turns the tool into a capital ‘E'. The case fitting is on the short, central leg and one of the two longer horizontal legs holds the cutter.
Before getting onto using the NT4000, I should mention a couple of things. Firstly, we're talking outside neck-turning. As the name suggests, metal is removed from external surfaces. Our first step is to resize the case, preferably with the expander ball assembly removed, then open up the neck with an appropriately dimensioned mandrel. This produces an inside case-neck diameter that gives a snug fit on the turner mandrel (not guaranteed using the expander ball in the sizer die), ensures the neck is true and transfers case-neck irregularities to the outside surfaces where the turner can get at them.
K&M and Sinclair International supply mandrels in two forms: expander and turner. The latter is around 0.001" smaller diameter than the former. Manufacturers have different ideas about dimensions so you want both from the same company. How do you use them? Sorry, I have to tell you that another bit of kit is required: a die-type body that holds the expander mandrel in your reloading press. The turner mandrel is the one used in the tool itself. So, we have four purchases: tool, two mandrels and expander-body. Well, that applies to Sinclair and K&M, but not Forster, Hornady or RCBS where you just have the tool with interchangeable turner mandrels as add-ons. One assumes that they are dimensioned to suit the expander ball in the respective makes of sizer die, with resizing done as usual with the expander/decapper assembly in situ. There is, though, a real risk the case will be a poor fit during turning - too loose and it will flop around, producing an inconsistent cut. Even worse, if it's too tight it will stick on the mandrel, get hot, and provide poor results as well as great difficulty in turning.
Lubrication is essential for both operations. The lube is applied to the inside neck surfaces during expanding, and smeared thinly onto the turner mandrel before starting work on each case. Only a few high-quality lubes are recommended for the latter task. The one I used is Redding/Imperial sizing die wax, which I also use for full-length resizing (obtainable from Norman Clark in Rugby). Turner mandrels are offered in stainless steel or much more expensive carbide versions. Carbide provides closer tolerances and more consistent results thanks to the hard material reducing friction and giving smoother tool operation.
We finally get to set up the turner itself. The NT4000 instruction sheet looked daunting, with 10 steps involving adjuster/lock screws and an adjustment knob. These were designated A to F on the diagrams, plus advice that further adjustment will probably be needed after the trial turning of a case. You need three different sizes of Allen key to move/lock the various parts. Actually, it's not difficult once you look at the tool and see the relationships between the parts. There are two things to set up - the first is length of the cut, which is determined by the position of the mandrel in the upright leg of our E. It incorporates a shoulder that stops further movement of the case into the tool. The correct position is that which allows the blade to skim the entire neck and just cut into the shoulder. The other variable is depth, determined by cutter position. An initial coarse setting is obtained using feeler gauges between it and the mandrel. An Allen-headed screw moves it in the tool body. With my Remy cases I locked it at a position where a 0.015" feeler gauge was a marginally loose fit. At this point, I'd better mention another preparatory chore. As the length of the cut is determined by the case-mouth butting against the mandrel shoulder, case length variations affect the results, so you must trim all cases to a common length before turning.
At last, we have resized, trimmed, neck-expanded cases and the turning tool has been set up, albeit coarsely. We now have to rotate the case on the mandrel to remove metal. Oh dear - more things needed! The traditional method is to use handles that grip the case around the web while you turn the case by hand. This is tedious and likely to cause repetitive strain injury if a lot of cases are involved. Manually turning necks destined for a small-dimensioned custom chamber requiring several passes is a very time consuming job. The modern way is to use a cordless screwdriver, also requiring a suitable case-holder. The specialist tool suppliers produce holders and drive-adaptors, but with this light task I got away with a Lee case trimmer stud and shellholder. It's not ideal as the case has a tendency to slide sideways out of the holder if too much torque is applied.
I used a budget 3.6V screwdriver rated at 200rpm. This was an ideal speed and a full charge did 50 to 60 cases. There is play in the drive-line inducing wobble, especially if metal is only being removed from part of the neck. The trick is to keep everything aligned holding the turner in the weak hand, the arm supported at the elbow and the turner held loosely so it wobbles in the hand letting it float. With my starter setting, the cutter edge was clear of the case-neck, requiring it to be moved in another couple of thou to touch. This is where things get tricky. The cutter locking screw has to be loosened and its adjuster tightened slightly, a skim taken and the resulting neck thickness measured. This process is repeated until the desired setting has been achieved by trial and error. The NT4000 incorporates a very clever method of getting there quickly - a large adjustment knob in the middle of the upright leg of the capital E. With a positive detent built in, each ‘click' of anti-clockwise turn moves the mandrel (and case-neck) 0.0002" (a fifth of a thou) closer to the cutter. A full two thou move of this knob saw the cutter just touch my first case and it was very easy to get to the 0.0155" setting from there. What I also found with my first couple of cases was that the length of the cut was too short, needing the mandrel to be set slightly deeper in the tool - this is the final adjustment Sinclair mentions in the set-up instructions.
Once the cutter is adjusted, the golden rule is to take one's time, feeding the case in really slowly and letting the cutter pull it into the tool. After ensuring that the full depth of cut has been obtained, the case is withdrawn slowly and the cutter takes a second skim, metal coming off as micro-thin ‘wire' for a smooth result. So there you are - one cleaned-up case; only another 199 to go, not to mention various other case preparation/sorting tasks to be done (table two)! This was just a clean so one pass was sufficient, but the removal of significant amounts of metal from cases to be used in below-standard dimension custom chambers requires two or more cuts. The initial one is coarse while the final pass only removes a tiny amount to give a high-quality, consistent result.
Cost vs. benefit
Let's look at cost. Starting with the financials, these can be reduced by buying the simplest tool you need, or better still buying it as a kit if you're a newbie to neck-turning. Sinclair International makes three models: the NT1000, 3000, and 4000. All are available in kit form, providing tool case-handles, Generation-2 expander body and expander and turner mandrels for one calibre (carbide type with the ‘Premium' kit using the NT4000). Dollar prices are US $90.75, US $106.95, and US $199.95, which at today's exchange rates are likely to be not far short of that in sterling after adding carriage, duty, VAT and dealer margin. A universal caseholder/driver kit adds another US $29.75 if you plan to use a cordless screwdriver, and this device also needs appropriate Lee Auto-Prime shellholder(s) for whichever case(s) you plan to turn. If you already neck-turn and are considering an upgrade to the NT4000, it costs US $145.95 as a standalone purchase, and carbide ‘turner mandrels' are priced at US $44.75 each (compared to $8.50 for the standard stainless steel version). Incidentally, I used stainless for the .308W clean-up and had no problems, but the carbide form will appeal to those looking for perfect results for benchrest or similarly demanding applications. The other cost is time, which is considerable even with power operation. If you are only likely to undertake clean-ups, the simpler tools are perfectly adequate, especially if you're only doing it for one cartridge and stick to one make of brass, so you only have to set the tool up once. However, the NT4000 tool is very easy to use and to re-set for different tasks, even for a neck-turning tyro like me. I found it easy to obtain good results first time round with the Sinclair two-mandrel system and this tool, so as always you pays your money and makes your choice. But - and this will be a big but for many readers - will neck-turning (and other onerous case-preparation chores) prove worthwhile, assuming we have a factory or minimum dimension chamber that doesn't require neck-turning anyway for utility and safety? That's not too hard to answer in two scenarios - yes if the rifle averages sub ½MOA five-shot groups with unprepared brass; no if it averages 1MOA and above. I'll stress averages as most MOA rifles provide the odd ½" 100yd group, and the owner conveniently forgets the more numerous 1-1½" results. Why am I confident 1MOA rifles don't benefit? I've read no end of investigations of the subject over the years in American magazines that proved case preparation was a waste of time and relatively accurate sporting and varmint rifles became no more so despite hours of work spent on the brass. Even with the
sub ½MOA rifle, using Lapua, Norma, or RWS brass exclusively will probably fit the bill, especially if necks are measured and some batching takes place.
The area in between is less certain. A rifle that averages 0.6 or 0.7MOA may or may not shoot better with prepped brass. I'll look at the larger issue later this year, using Remington and Lapua brass with various degrees of preparation from nil to full, and sized/loaded with a variety of tools and dies in my ex-police Parker-Hale M87, which is now rebuilt by Norman Clark in .260 Remington with a Krieger match barrel.
While neck-turning is part of preparation for the 2009 season, my next subject harks back to last year. It can be said to have been born out of desperation from a struggle to persuade a 24" barrel .308W rifle to perform at 1,000yd. While 600yd performance was superb, (I got a near-perfect score in the Yorkshire Spring Open) and 800yd saw me very pleased with the rifle and ammunition on those occasions I got everything right, 1,000yd was a different matter. The majority of national F-Class league matches are shot over this range.
The problem wasn't accuracy. The 175gn Sierra Match King (SMK) load I'd worked up the previous winter provided group after group that only varied between 0.3 and 0.4" at 100yd, with 10-round MV spreads under 20fps, sometimes 10fps. It shouldn't have been the bullet; the 175gn SMK is designed for long-range shooting at modest velocities, and a popular choice with American F/TR shooters including champion Brad Sauve. 2,640fps MV should have kept bullets supersonic at 1,000yd in any normal environment. Sierra ‘Infinity VI' predicted that even in the near-freezing temperatures we saw in round one at Diggle in April, they'd still be doing 1,180fps at the target, 50-odd fps above the speed of sound. However, readers will be aware of my scepticism about long-range ballistics models at marginal velocities due to the inadequacies of ‘G1 drag curves' and the effect of transonic zone turbulence (Target Sports September 08 and October 08 issues). Something was causing variable performance at this range, as seen by poor elevation consistency - half the shots would be fine while the others were all over the place, especially if there was any headwind.
There were two possible responses (apart from replacing the barrel/rifle with something of a more appropriate length) - develop another load that provided improved performance (to be covered next month when I return to .308 handloading), or find a quick fix that improved the existing load's performance slightly. I decided that a marginal improvement would do the trick. You'll ask why I didn't stick another grain of powder into the case for another 75 or 80fps, but while there was plenty more
velocity available, up to 2,800fps with this bullet, accuracy deteriorated badly as soon as relatively low MV thresholds were exceeded.
The ‘quick-fix' I had in mind was a Whidden Gunworks bullet-pointer, a Forster Ultra-Seater die based tool that forces the bullet tip into a cone shaped depression machined into one end of a cylindrical block of steel held inside a duralloy sleeve inside the die body, most of the Forster internal parts retained to hold and tension this pair. The bullet tip is swaged into a sharper point, the process almost closing the hollow-point up. It is not a cheap device (US $250 including one calibre-specific sleeve and US $40 for each additional sleeve). Whidden says one can expect to see treated bullets strike around 1MOA higher at 1,000yd reflecting the slight improvement in BC, as well as improved elevation consistency through all bullets now having near identical meplat diameters. Small calibres see the greatest improvements, because the meplat width tends to be larger in relation to the bullet diameter. The tool is set up in the reloading press like any normal die, a standard 308 type shellholder installed in the ram and a small steel platform (supplied) clipped into that for the bullet to sit on. One adjusts the tool screwing the micrometer die top in or out until the bullet tip contacts the appropriate internal surface with the ram at the top of its travel, then keeps on screwing it down until the desired amount of pointing occurs - simple. 100 bullets only take a few minutes. Pointed bullets have a distinctive tip shape and their main benefit is a small reduction in wind-induced drift. Since getting the tool, I've regularly noticed them in other competitors' ammunition boxes at national league rounds, so the practice is fairly widespread - unsurprising, as everybody is looking for that extra edge.
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