Target Sports

HANDLOADING: A TWIST IN THE TALE

Created on 14th May 2009

LAURIE HOLLAND tries to find an improved load, looking at twist rates and concentrating on the heavier bullets

LAST MONTH I mentioned my frustrations in trying to compete in 1,000yd F-Class competitions with the FN SPR and its 24" 12T barrel. This was the spur for further handloading experiments to find an improved load. The problem didn't just lie in the barrel length, as the Winchester M70 magazine action didn't like really stiff loads. This is not a criticism of the rifle which was never designed to be competitive at this range against single-shot target rifles. How about other out-of-the-box tactical rifles? The Accuracy International AE and Sako TRG have 650mm barrels (25.6"), the Remy 700s (PSS and VS) 660mm (26") the extra length giving an extra 60-80fps MV that can make all the difference at 1,000yd. Even so, if you want to compete seriously in national F/TR, you need a rifle with a rigid single-shot action and 30-34" barrel to get 155gn bullets to over 3,000fps, or 210gn VLDs to 2,550fps plus.

Making small holes smaller

I'd only intended to use the SPR for one, maybe two, national F-Class League rounds, having two new .308W rifles in the pipeline. However, American precision barrel-makers take forever to deliver anything these days, and both projects ran six months or more behind their original estimates despite barrels coming from different makers. Hence the search for ballistic aids, one being the Whidden Gunworks bullet pointing die mentioned last month. That helped, but unfortunately not by enough. I'm sure that some readers will have looked at the images and wondered whether reducing the size of such a small hole makes a difference. I can only say the ballisticians assure us it does. Why have one at all? Forming the shoulder/point is the final major operation, the finished bullet ejected from the swaging die by an integral sliding pin. You cannot do this to a bullet with an overly small meplat as there has to be sufficient area for the pin to bear on without damaging the bullet nose (as you often see on poorly made milspec FMJ bullets). Pointing is an extra standalone operation which is why no major manufacturer has done it until now - we'll have to see if Sierra starts a trend with its new 155gn Palma MK No. 2156.

How much does pointing improve the BC? There is no set percentage, it depends on the bullet's shape and efficiency. If it's a high-BC design, as in the heavier 6.5 and 7mm match bullets, you get little. If it has a relatively low BC as in 155gn .308s, and .224" bullets of all weights/designs, you can get a noticeable boost to the BC that may see the bullet fly 1MOA or more flatter at 1,000yd as seen on the sight settings, also needing less windage. Moreover, meplat trimming followed by pointing keeps every bullet's BC within a small range to help persuade bullets to behave consistently. If this is getting too much, don't despair! Buy Hornady A-Maxes, the sharp plastic tip does it all for you. Anyway, you can forget this malarkey unless you shoot at 800yd and up (600yd benchrest competitors possibly excepted).

There is another trick long-range precision shooters use to help get consistent ballistic performance at long ranges - measuring bullets with a comparator, batching as required. Traditionally this was done from the base to the start of the full-diameter section behind the ogive, but many competitors now go further, comparing the bearing surface lengths in their HPBT bullets using two comparators, one on each calliper jaw. Since I only have one, I did the former with my 190gn Match Kings and found enough variations to make it worthwhile to batch them.

Let's twist again!:

Returning to the FN SPR, there was another reason why I wanted another round of load development - the rifle had a limited remaining lifespan in .308W as it was going to be rebarreled to 6.5X47 Lapua at the end of 2008, come what may. Since neither replacement has a 12" twist (12T) barrel, one 10T, the other 13.5T, there were only a few months left to see what could be done in a rifle whose barrel uses the cartridge's ‘standard' twist rate. Few target shooters specify 12T in a custom rifle or rebarrelling job, as they either want to use 155s at high MVs in 13-13.5T barrels, or 190-220gn models that need 10-11T. So far as ‘tactical' rifles are concerned, some makers like Accuracy International go for 10T as military customers always err on the side of theoretically over-fast bullet rotation to ensure long-range performance in extreme cold. American companies primarily sell these rifles to law-enforcers and use 12T as it is well suited to the factory 168gn and 175gn bulleted match ammunition that is standard issue for most such users. 12T also stabilises 180gn Sierra MK and 185gn Lapua Scenar bullets despite an extra 1/10" length. The recommended minimum Sg (Gyroscopic Stability Factor) of 1.4 is available at 2,600fps (table one). How about 168 to 185gn VLDs, which with their secant-ogive form are usually longer than equivalent SMKs, or the 190gn Sierra Match King? Lapua quotes 10T as the ideal twist rate for its 185gn D46 rebated base FMJBT, and its length (which remember, is normally the deciding factor in this issue, not weight) is considerably shorter than that of the 190gn SMK and 185gn Berger VLD. Yet Berger quotes 12T for the latter, an apparent inconsistency. This is partly down to construction differences, the SMK and VLD HP designs incorporating a void ahead of the core inside the jacket, while the FMJ-form D46 has lead from end to end. That and the rebated boattail move the centre of gravity forward compared to a HPBT design requiring more stabilisation, hence a faster twist rate. (The D46's long history is probably more pertinent, this bullet originally developed for Finnish army 7.62X53R machine guns with 10T barrels.) A conversation with John Carmichael of HPS-Target Rifle, a long-time .308W Match Rifle competitor before he joined the F-Class circuit, confirmed the 190gn SMK should work in my barrel's 12" twist.

Bullet choices:

The objective was to have every bullet comfortably supersonic at 1,000yd irrespective of conditions, a matter of getting the right combination of MV and BC (ballistic coefficient). In practice it's a choice between two options - a light, lower BC bullet that exits the muzzle at a high MV, or a heavy, more ballistically efficient design starting out 200-300fps slower (up to 500fps slower in 32-34" barrels). Experience in TR and Palma has shown that 155s need 2,950fps to perform at this range, and many F/TR competitors are running 100fps above that. My first round of load development (reported in the November 2006 issue of Target Sports) had seen best results with the 155gn SMK and Scenar between 2,550 and 2,700fps in this rifle. RG Bisley Match and HPS Target-Master saw MVs in the 2,720-2,750fps range, these presumably producing something approaching maximum pressure levels, so there was little chance of finding another 250fps MV with safety and accuracy, and I didn't even try.

This round of tests therefore concentrated on the heavier bullets using my existing match load of 175gn SMK and 43gn of IMR-4064 as the benchmark. It produced just over 2,600fps in cool conditions, and I was initially very happy with the accuracy, a winter 300yd benchrest competition seeing a four-group average of 1.91", the smallest 1.549", on a blustery day for example. Squeezing another 100fps out of this bullet to get it up to 2,700fps had to be an option - provided accuracy was retained, since a load that cannot achieve 1/2MOA groups isn't worth using in this discipline irrespective of its ballistics.

Although its 168gn and 180gn siblings are listed in table one, these designs don't work beyond 900yd, so forget them. I'd tried the 185gn Lapua D46 FMJBT previously with relatively poor results, so it was ruled out. That left the 185gn Lapua Scenar with a claimed BC of 0.521 and the 190gn SMK at 0.533, worthwhile improvements over the 175 SMK's 0.505, providing I could get MVs up to the 2,625 - 2,650fps mark. That looked possible as limited testing with the Scenar in 2006 had seen reasonable accuracy at 2,624fps using Vihtavuori N550 ‘high-energy' powder. Likewise, Norma ‘Diamond Match' factory cartridges loaded with moly-coated 190gn SMKs had achieved 2,628fps. Unfortunately, the best group achieved with the Norma fodder was barely under the inch.

I had some more contenders since my original tests - Berger 155, 168, 175, and 185gn Match VLDs with claimed BCs from 0.439 to 0.549. The points made about safely available MVs from the 155gn Sierra and Lapua bullets in the SPR also apply to the Berger, likewise the 168gn VLD whose 0.473 BC is below that of the 175gn SMK. They would need MVs significantly above 2,700fps to give any real benefit, which I wasn't confident of achieving in the limited time available before the next F-Class round. Incidentally, the Bergers' BCs were obtained from the company's website, and sharp-eyed readers will have noticed they look low - Berger recently revised BCs on its entire range using a new methodology that gives lower but more accurate results for the typical user. The company quotes a required twist rate of 12" for its long 185gn VLD, but I had my doubts and omitted it, working up two combinations each for the 155 and 168gn VLDs purely out of interest, and three for the 175gn version. Why bother when there is apparently no ballistic advantage? One reason was as for the two lighter Bergers, taking advantage of the window of opportunity to try more bullets in the 12T SPR, another being that the Bergers with thin jackets and relatively short bearing surfaces can sometimes be driven to higher MVs than equivalent SMKs at safe pressures and with good accuracy.

Type S

All test combinations used Russian manufactured PMC primers that give excellent results, and were among the cheapest available, which they unfortunately no longer are. Bar one combination with Norma brass, Lapua cases were used throughout. I'd used a Lee collet die set for my .308 ammo for over 20 years and had prepared so many cases with it I wore the original sizer die out years ago. This die neck-sizes cases with the advantage of doing the job easily and quickly, but I increasingly full-length size my cases nowadays, especially for ammunition used in factory rifle chambers. I use Hornady/Stoney-Point headspace gauges to ensure the case-shoulder is barely set back. Checking cartridge concentricity earlier in the season had revealed more examples with significant bullet runout than I was happy with, so this was an excellent excuse to both switch to full-length sizing while upgrading my kit to a Redding Type S bushing sizer die and Competition seater. The Type S uses interchangeable bushings available in 0.001" gradations and in addition to being superbly made, reduces the amount the neck brass is worked to a minimum. I'll look at these dies next month, so won't say any more about them now. Incidentally, FN claims the SPR is built with minimum headspace, and this appeared to be true, the sizer die barely touching fired cases' shoulders at the default setting in the press with its body hard on the shellholder.

Satisfactory

Let's move onto the results of the exercise, and to avoid unnecessary stress and tension building up among readers, I'll say now that the limited objective of marginally improved long-range ballistic performance allied to satisfactory accuracy was achieved. My scores in the September round held at Diggle improved significantly so I was no longer last in class. Table two tells the story in detail, but as always here are some comments to flesh out the bare bones.

I said my previous match load was used as a control load, so that meant retesting it, and I got a nasty surprise. The MV had risen by over 40fps, and groups opened up markedly, some to well over the inch with the increase mostly lateral. This could have been due to the IMR-4064 powder generating more pressure in warm weather, more likely a new lot of the powder being ‘hotter'. The good news was that the overwhelming majority of shots stayed inside half to 3/4MOA, odd ones thrown out a half inch to either side. This was in line with the rifle's behaviour during load testing with combinations that weren't quite right. The moral is to check that a load worked up in one set of conditions works in others, and recheck it with a new batch of powder. (You will most likely get away with not doing so in the latter situation with Vihtavuori powders as they are pretty consistent from batch to batch.)

Six of the seven Berger VLD combinations produced groups around the half-inch, several better, but the smallest groups were all seen at modest velocities. The odd man out was the 175gn bullet with Viht N150 which I had expected to do well, but the top load was only producing 2,571fps, so working charges up another grain or two might have improved groups with reasonable MVs, but there wasn't time to try. This bullet did well with N550 group-wise, but the weather kept the chronograph in its box that day, so I don't know how fast they were going. Incidentally, VLDs often perform better at longer ranges than 100yd results predict, a 3/4" 100yd group say, shrinking to under 1/2MOA at 300.

As well as would-be match loads, I'd also tried an old American short-range favourite, a relatively heavy bullet with a modest charge of 4895, the 175gn SMK with the Hodgdon variant of that powder here. 41gn gave a lovely rounded half-inch group at only 2,420fps, very pleasant to shoot. 42gn of Viht N540 gave identical results - 0.3" at 2,406 - not that a light load was intended here! With Viht's maximum producing 2,580fps and moderate pressure signs, this reinforced suspicions that the company's loads-data is on the light side, for my batch of the powder at any rate. Other 175gn SMK combinations with Reloder 15, N550, IMR-4064 and 4320 did the business velocity-wise, maximum loads producing MVs ranging from just shy of 2,700fps to 2,750. However, accuracy disappeared every time I got near these speeds.
Of the three loads tried with the 185gn Lapua Scenar, only Viht N550 managed to provide the accuracy I needed, but again at too low MVs, topping out at 2,579fps. Another go with higher charges was justified, but not pursued because of time pressures with the September competition fast approaching. So that left my great white hope, the 190gn SMK. VarGet disappointed. (Actually this rifle didn't like the powder in any combination, which is unusual as it is universally popular in .308W.) IMR-4064 saw groups shrink as loads rose, and would have been worth further development if there had been time. N150 produced good groups, but was again 100fps short of what was needed. Finally, success - 46.5gn of N550 produced a half-incher at 2,638fps. A follow-up test increasing charges in 0.2gn steps repeated these results with 46.5 and 46.7gn, the latter chosen with only days now left before the September Diggle round, hoping it wasn't a one-off fluke. It probably wasn't optimal, but it still shot much better than the previous 175gn load in both 1,000yd stages. Ian Dixon did tell me it produced an almighty muzzle blast however! Bullets were measured to the ogive, batched, trimmed and pointed - every little helps as somebody on the TV keeps saying!

Anyway, 21 September 2008, day two of round five of last year's F-Class championship, was the rifle's swansong. It was handed over to Walker Rifles at the end of play for rebarrelling after nearly four years and as many thousand rounds through it as a .308.

Important notice
These components and loads performed safely in the author's rifle. This cannot be guaranteed for other handloaders and rifles. Good handloading procedures should be used at all times, working loads up from recommended starting levels and looking for signs of excessive pressure or other problems.