HANDLOADING: SLOW BURNERS
Created on 14th May 2009
LAURIE HOLLAND completes his tests on the WSSMs and takes a look at some brand new products on the scene
FINISHING THE .243WSSM saga off, this version of the cartridge also gave best results with slower burning powders - Alliant Reloder 19; the various 4350s; Hodgdon H4831 (use the ‘sc' version as top loads nearly fill the case giving compressed loads) and Viht N160. I could add Reloder 22 and Viht N560 to that list too. With hindsight, I wish I'd tried slower burning powders with the 70gn Sierras rather than those that had worked well with this bullet in the .243WCF, despite the advice in loading manuals to use mid-range burning speed powders with lighter bullets. Moving onto bullets, I finally found one that suited the cartridge, rifle and barrel, the 90gn Nosler Ballistic Tip. This performed well with all slower burning powders tried, producing groups on or under the half-inch. (Gunsmith Norman Clark had suggested I try Noslers as they have a jacket design that employs a massively thick heel, so will take high pressures.)
By the time I got around to trying the two 100gn Sierra deer bullets, strange things were happening. Cleaning the barrel between test batches produced a film of granulated gilding metal residue on the first patch. This suggested the barrel-throat was now badly eroded and had become so rough it was acting like a coarse file to abrade material from the bullet. At the very end, combinations using thin-jacketed varmint bullets saw a major deterioration in group size. Other shooters said they could see a ‘white streak' travel down-range, suggesting bits of the jacket were sticking out and causing air turbulence. A couple of final batches with 55gn bullets were fired solely to obtain MVs. Most shots hit the paper, but groups were now 4" plus. Barrel life was barely 1,000 rounds, so the chrome plating hadn't extended it much. (Conversely, 350 rounds hadn't worn the .223WSSM's Krieger match barrel's throat measurably. I found the settings that saw various bullets engage the rifling using a Hornady OAL tool on receiving the rifle from the Southern Gun Company. On finishing my tests I repeated the exercise - they were nearly identical, to my surprise.)
So what conclusions did I come to about these short, fat cartridges? There is a case for the .223 version if you must have absolute maximum velocity. There is also logic to employing it in a heavy fast-twist match quality barrel with 80 or better still 90gn bullets. However, I can't see any good reason for the .243 Wuzzim's existence! It gives a marginal performance improvement over the .243WCF at the expense of shorter barrel life, a thick-walled case, hard extraction, and expensive factory cartridges. The handloader is restricted to Winchester brass while there is a big choice with the older cartridge. Damningly, the short magnum also appears more likely to cause unpredictable pressure-related problems. You might remember I mentioned the odd incident of apparently over-high pressures generated by a single cartridge out of 20 despite it being a mid-level (and weighed) load. On photographing the case-head with a macro lens, the enlarged image showed at least three sets of pressure-marks. That case had either suffered a serious overload with nearly every test combination it had been used with, or more likely, came from the factory with over-soft brass.
Let's move onto new products for a new year. Alliant introduced Reloder 17, a ‘double-base' (nitrocellulose plus nitroglycerine) rifle powder, in the middle of last year. As the designation suggests, its burning rate is nominally between that of numbers 15 and 19 which should make it comparable to those of Viht N150/N550 and the 4350s. Unlike other powders in the ‘Reloder' range, it is manufactured by Nitrochemie AG in Switzerland, the older products by Swedish company Bofors. It is claimed Re17 burns cleanly producing excellent accuracy and small velocity spreads. Its main selling point, though, is higher MVs from some cartridges, especially the short magnums. It does this through using ‘deterrent' additives (which slow combustion) as an integral component of the propellant, not a coating on the outside of the kernels as is the norm. This flattens the pressure-barrel time curve and gives a longer period of high pressure behind the bullet. It is also fine-grained, so a greater weight can be loaded in cartridges where case capacity is the limiting factor.
This powder has caused huge interest in the USA with reports of 100fps plus MV gains in various cartridges. Even as much as 200fps was seen in 6XC match loads with the 115gn DTAC bullet, giving it the status of ‘wonder propellant'. With experience, it seems to be a bit slower burning than first thought so performs best in loads where the 4350s, 4831s, and N160 are the norm. The really big MV increases are delivered in cartridges where its density allows the case to hold a heavier charge than existing bulkier alternatives. This applies to the short magnums and that increasingly popular long-range match cartridge, the .284 Winchester with heavy bullets. It produces more modest increases in numbers like the 6.5-284 Norma which have plenty of room. Overall, it looks an excellent new propellant for cartridges that use ‘slow burners', but don't get too excited and rush down to your local dealer to buy a can. The initial supply sold out in record time across the Atlantic, and a second shipment expected to arrive in late December 2008 was allocated to meeting back orders from dealers there.
Berger Bullets has been busy with new products and some changes to existing ones. One or two new VLDs (Very Low Drag designs) such as the 130gn 6.5mm have recently appeared. This bullet is probably primarily intended for loading in the 6.5 Grendel and 6.5X47mm Lapua. The company has made rapid progress on its promise to offer tangent ogive alternatives to most of its heavier secant-ogive VLDs. These ‘Match BT' bullets have a slightly lower ballistic coefficient, but the ogive shape makes them ‘jump-tolerant', therefore easier to fine-tune in a handload. Taking 6mm as an example, we now have 90, 105 and 108gn Match BTs, and 95, 105 and 115gn Match VLDs. Comparing 105s, the VLD has a claimed BC of 0.556 while the BT version is 0.527. Running the pair through the Sierra Infinity ballistic program with 3,000fps MV, the VLD is calculated to be travelling at 1,544fps at 1,000yd with the BT 46fps slower. In a 10mph crosswind, the BT version drifts an extra 4" at 74.43 versus 70.44", so performance differences are small. Another innovation is four new models listed as ‘THICK' - nothing to do with intelligence, rather jacket thickness, theirs greater than the standard versions which continue unchanged. The quartet comprises 140gn 6.5mm and 180gn 7mm models, each in BT and VLD form, the reason being that the thin J4 jacket normally used suffered the occasional failure in very high pressure and velocity loads.
Perhaps the most interesting bullet developments for many British fullbore competition shooters are new 0.308" 155gn Palma/TR models, from Sierra as well as Berger. Berger's version is called the 155.5gn Match BT FULLBORE and the UK's distributor Norman Clark has it in stock. So what's special apart from ½gn extra weight? Look at the BCs - existing 155gn Sierra Palma MK highest claimed value 0.450; Berger 155gn Match BT 0.453; Berger 155gn VLD 0.472; new 155.5gn Berger 0.486. So, it's a super-VLD then?
Actually, it is a tangent ogive form and so is easy to get it to shoot well. The Sierra model is due out of the factory in early 2009 and hasn't been named at the time of writing, but is also a high-BC tangent ogive design. Prototypes were given to US Palma Team members at the Spirit of America matches at Raton, New Mexico last September. Existing Palma MK bullets were pulled from the .308 Win cartridges before matches and simply replaced by the new model without load development. Despite this, users reported excellent accuracy and they shot around 2MOA higher at 1,000yd, also requiring less windage than the older design. They must have performed well - the team won the ‘America Cup' matches, with Australia second and Britain third.
These new 155gn bullets have implications for our Target Rifle as they will inevitably be loaded in commercial .308W match ammunition. Existing commercial products loaded with the ‘old' 155gn Palma MK only provide modest benefits over 155gn RG 7.62mm fodder. That will change with either of the new bullets, a step change in ballistic performance and accuracy likely. The current NRA contract with Radway Green is described as interim. This means the NRA will face an interesting choice over ammunition performance versus cost whose outcome could have long-term effects on this discipline's development and health.
How have Berger and Sierra managed to provide higher BCs than existing VLD designs despite using the tangent ogive form? It's down to the length of the shoulder, these designs having exceptionally long examples produced at the expense of the middle section bearing surface. The Sierra prototypes used at Raton had also been pointed - the open tips closed up as a final manufacturing operation. Does it mean we'll see a new generation of such bullets in other calibres too? This is unlikely. Most older .308/155s are short and relatively blunt compared to heavier 6.5 and 7mm match bullets, hence benefiting greatly from a bit of stretching and streamlining.
Let's move onto tools for working on case-necks, but first, a warning. If you handload for a 0.303" Enfield or skinny barrel sporter with a slack chamber, carry on reading by all means, but please don't waste any money on these tools - you won't get value for your outlay of cash and time. What we're looking to do is to identify variations in neck wall thickness and rectify them. Variations come in two forms - between cases and within them. Let's take the first issue. You've bought a couple of hundred new cases which you've inspected for faults, trimmed to a common length, run through the sizer die to iron out small dents, and chamfered the mouths. They're new, shiny-beautiful, absolutely perfect, ready for priming and loading. Or are they? I've previously mentioned punched primer flash-hole burrs and primer pocket depth/uniformity, weight variations and more! Let's forget these issues and concentrate on necks this month and next to see if I can justify acquiring some nice new tools from Sinclair International.
Let's say the 200 cases have an average neck-wall thickness of 0.015" (15 thou). One example might have that exactly, while the next has 0.014" and the one after that 0.016". At this stage, let's assume each case is consistent within itself - this is good as the sized case should be concentric. If the press and sizer die are up to the job we'll produce finished ammunition with little bullet-runout. So, where's the problem? Neck wall thickness affects ‘bullet-pull'. This means that on firing, the level of internal pressure created by the powder charge burn needed to move the bullet out of the case and into the leade will vary. Smokeless powder doesn't burn in a consistent way - the higher the pressure, the faster it burns. So, if we have a thin neck providing less bullet pull than the norm, the bullet might start to move out of the case at 500 or 1,000psi less pressure. As it moves forward it increases the effective combustion chamber volume reducing pressures which slows the rate of burn. Variable cartridge behaviour produces different stresses on the firearm affecting receiver and barrel vibrations and groups open up. As we fire, resize and reload these cases, varying thickness also influences the rate and degree of work-hardening of the neck brass, so bullet-pull differences will increase.
The other type is within a case, such as the neck-wall being say 0.014" thick on one side and 0.016" on the other. This affects the concentricity of the finished cartridge so the bullet may not point straight down the middle of the barrel on being chambered. Not only are bullets askew, but each cartridge chambered is likely to produce the effect in a random manner, bullets inclined in different directions. Even though the amounts involved are tiny, bullets enter the rifling at different attitudes affecting how they behave. How much variation might you find in a box of new cases? American benchrest shooters write about finding six thou within individual cases in batches of US commercial brass not too many years ago, but we expect far less today.
How do you measure case wall thickness? The precision way is with a tubing micrometer, or specialist case-neck equivalent. They read to 0.0001" (1/10 of a thousandth of an inch), are expensive, and take some practice to use well. If you fancy your hand at benchrest competition involving heavily neck-turned 6PPC cases, you work to these tolerances and need such a ‘mike'. The rest of us don't need to measure things to this precision and also want to do this job more easily and quicker. Sinclair International has long had a simple hand-held L-shape neck measuring tool that places the case on a spindle (they call it an ‘alignment rod') that fits into the case flash-hole. The case-neck sits on an interchangeable stop/bushing (‘neck-pilot') while holding a cheap 0.001" dial gauge tip against the neck. An updated version appeared last year that sees the tool permanently installed on a small but heavy and stable nylon base for use on a table or bench - more expensive, but easier and quicker to use.
Unfortunately, the outlay doesn't end with the purchase of the tool as it requires a neck-pilot for each calibre (not cartridge) that you're going to measure. If you're into .17 or .20" calibre cartridges, the standard ‘alignment rod' doesn't fit, so you have to buy a small diameter carbide-steel version. Sinclair sells its own stainless steel pilots, or you can use RCBS Flash-Hole [trimmer tool] Case Pilot Stops.
The Sinclair tool is easy to set up and use. It simply requires the rod to be set at the correct length for the case, and the appropriate stop slipped on and locked into position. It's then a matter of zeroing the dial gauge on the stop body. Grip the top end of its operating rod to draw the tip clear of the stop and slip a case on before gently lowering the tip onto its neck. Cases are not a really tight fit on the stop body but the gauge exerts enough pressure to press them against it and give an accurate reading. Then, rotate the case to different positions to obtain three or four readings, noting them. This is best done by lifting the gauge rod each time to avoid its tip scoring the brass. After you've noted several readings, you get a feel for the range of values involved. At this point you measure every case and cull out any bad ones and/or sort them into sets. Table one lists the results obtained from samples of 25 new Lapua and Remington .308W cases measured at three points. The Remy sample surprised me by having a smaller maximum variation within any single case than the more expensive Finnish products. Lapua provided a higher percentage with less than a thou variation. Both had a similar average thickness around 0.016", the Lapuas marginally greater, while some Norma cases averaged over two thou less. If a cull plus sort option is adopted, it's best to have 200, better still 300, cases to work with to produce usable sized batches. There is another option - to apply a light neck-turn cut to ‘clean them up', this obviously requiring more tools, expense and time. Next month, I'll look at whether this is justified, what's involved in simple neck-turning, and try my hand with a new, easy to set up neck turning tool from Sinclair International. I'll also look at another expensive boys' toy designed to help squeeze the last bit of ballistic performance from bullets at extreme ranges. This will link into a report on my ongoing attempts throughout last year to produce .308W handloads that would perform at 1,000yd from a 24" barrelled FN SPR rifle. (If I tell you the rifle has been since rebarreled to 6.5X47mm Lapua, this may give the game away!)
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