Target Sports

HANDLOADING: TO INFINITY AND BEYOND

Created on 14th May 2009

LAURIE HOLLAND takes a look at the latest version of the Sierra Infinity ballistics software and finds it surprisingly easy to use

THIS MONTH I'll be looking at the latest edition (Version 6.0) of the Sierra ‘Infinity' package to see what state-of-the-art ballistics software can do for us. However, before starting on that here is a short update on last month's topic, the .30 Carbine. Southern Gun's Bob Clark tells me that he provides modified .223 Rem magazines for his AR-based .30C rifles, which accept cartridges loaded above standard COLs - well above, right up to the 223's 2.25" compared to the .30C's normal maximum of 1.68" - allowing heavy bullets to be used, seated well out. So, magazine feed is on for longer sharp-nosed bulleted rounds like those I produced with the Lapua 123gn FMJ. Equally significant, ‘long-range' cartridges may be loaded with FMJ and HPBT match bullets, seating them shallowly to maximise the powder capacity and MV at acceptable pressures. (Flat-base is preferable as it is suited to very shallow seating, taking up less case capacity.) Bob tells me that he and some LAC30/SSR-30 owners worked up loads with 123-150gn 0.308" FMJs above Alliant 2400 that achieved MVs over 1,800fps with the lighter bullets.

I modelled a few combinations on QuickLOAD with Lapua's 123gn 0.309" FMJ seated at a COL of 1.90", and the same company's short boat-tailed lock-base 0.308" 150 and 170gn match FMJs at 2.1". Results suggested MVs approaching 1,900fps might be possible for the 123-grainer, 1,700 for the 150, and 1,500 for the 170 from a 20" barrel. Figure one compares the 300yd ballistic performance of a standard 110gn RNFMJ load at 1,950fps against 123 and 150gn handloads of the same velocity, as well as including a .223R 69gn Sierra MK load at 2,900fps for reference. Loads of 123/150gn .30C fall between the other two ballistically, and remain supersonic beyond 300yd. Bob says similar loads have given 1 MOA or better accuracy at 200yd. So, even if QuickLOAD has overestimated the MVs, it's obvious that .30C performance can be transformed in the SGC rifles. Nevertheless, why bother with it when even ‘super-loads' are ballistically inferior to .223/69? The answer depends on whether you want to use the rifle on pistol calibre carbine ranges where the .30C version reverts to 115-125gn lead bullet handloads that meet range license conditions, an option not open to the .223R. (The SGC models retain this option using standard M1 carbine magazines and an adaptor.)

Ballistics programme

So what can we do with external ballistics data? At the most basic level, the century-old Ingalls-type trajectory tables list bullet velocities, rise/drop and wind drift over specified distances and also at intermediate points, for a bullet with a known ballistic coefficient (BC) and MV. The results vary according to the distance at which the rifle is zeroed. (So, for a rifle zeroed at 500yd, the amount of times the bullet strikes high will be shown typically at 100, 200, 300 and 400yd points; 0 elevation variation applies at 500yd; then there is an increasing amount of drop below the aiming point at each subsequent 100yd mark.) Another row in the table often shows the distance the bullet is moved laterally at each range by crosswinds (90º angle), typically at five, 10 or 20mph. One should note that velocities and hence trajectories are calculated by comparing the bullet to a ‘standard projectile' with a BC of 1.0. This process involves factors which may affect the accuracy of the results, especially at long ranges - an issue I'll touch on next month.

Uses are to identify elevation sight setting changes to get from one distance to another; to check whether the bullet remains supersonic at the target (or retains sufficient terminal energy to kill the quarry cleanly); and to identify wind drift. Ballistically clued-up sporting shooters may identify a zero for a maximum point-blank range (PBR) to suit the size of the kill zone (where an optimally zeroed rifle hits within the zone without the sights or aiming mark being altered).

MOA and mils

Traditionally, printed tables provide results in inches and the target shooter who thinks in minutes of angle (MOA) does some arithmetic based on 1MOA = 1" at 100yd. This increases proportionately by distance, so a 10" correction needed at 1,000yd is still 1MOA on the sights. (Actually, a single MOA is 1.047" at 100yd, but rounding to the inch is close enough.) So when the old Sierra fourth edition reloading manual tables advise that a 0.308" 155gn Palma MK at 2,900fps MV and zeroed at 300yd strikes 30.52" low at 500yd, one divides this figure by five to see a 6MOA change is needed. (In my experience this is optimistic - I needed 6½-7 when I shot TR with this bullet.)

Military snipers, police marksmen and an increasing number of sporting shooters use riflescopes with Mil-Dot reticles with some, such as the Schmidt & Bender ‘P4L Fine', having intermediate half-mil marks (Figure two). The distance between the dots or hash marks equates to 3.6MOA, so a police officer with a .308W rifle zeroed at 200yd who estimates the target range at 300 and the wind strength equating to 10mph at 90° can take a snap shot by holding around ¾ mil high and a fraction less correction than this in the direction the wind is coming from. This is on the basis of ballistics tables saying that Lapua or Federal 167/168gn factory match ammunition will strike 8-9" low and 7-8" downwind (approximately 2.5 and 2.25-MOA respectively) in the absence of sight adjustment.

Computers

Printed tables have limitations, especially the truncated versions found in reloading manuals that are restricted by space in the ranges covered and zeroes included (Figure three). Moreover, unlike the military, for whom Ingalls tables were originally compiled, civilian competition shooting (TR aside) now sees much experimentation with bullet shapes and weights and cartridges and calibres to achieve a competitive edge. Even the ‘starter' F-T/R class involves choices, initially between .223R and .308W. Figure four shows why .308 is the invariable choice in National League rounds. There is a less clear-cut debate over fast rifling twists and heavy bullets versus slow-twist and 155s.

What this tells us is that many shooters need more than simple velocity/drop/drift tables. The ability to easily model different bullet MV combinations and compare the results over various ranges is particularly desirable. Traditional tables use standard conditions - altitude, temperature, barometric pressure, and humidity - but what if you don't shoot in a standard environment? Looking at the effects of wind at a constant strength and direction is useful for comparing bullet performance but rarely reflects real range conditions, which may have vertical components and see directional and/or strength changes during the bullet's flight, thanks to stands of trees or other range features. If you've got a pad of graph paper and can spare the time, you can draw velocity and trajectory charts to compare bullets. These tasks are tailor-made for the home computer and its increasingly sophisticated graphing abilities. I used the external ballistics calculator component of RCBS.Load software for years - easy to use, but requiring some dexterity to calculate wind drift as well as a lot of back of envelope notation for meaningful comparisons. Then I obtained a copy of Sierra's latest version of the Infinity ballistics suite and things have become much easier.

Version 6.0 of Sierra's Infinity software is designed for Microsoft's latest PC operating systems Windows Vista and XP. If you're an XP user like me you also get the essential Microsoft Windows .NET Framework 2.0 support platform. As well as rewriting the suite's ‘operating system', Sierra has added enhancements. (Version 5.0 is still available for use with earlier Windows operating systems.) After loading you get a fairly simple display with a toolbar comprising words and icons (Figure five). Standard Windows drop-down menu commands aside, there are six specific areas of the software: ‘Load bullet', ‘Trajectory', ‘Operations', ‘Trajectory variations', ‘Help', and ‘Calculators'. The last named produces the smallest menu of two (recoil and rifling twist) while ‘Trajectory' is the largest with nine routines, a couple of which lead into sub-menus. Underneath them we have nine shortcut ‘buttons': ‘Edit custom bullet' (to input details for a bullet that doesn't exist in the bullet database); ‘Chart view'; ‘Graph view'' ‘Hide grid'; ‘Show values'; ‘Zoom', and ‘Normal trajectory' plus print and print preview icons. These mostly relate to how results are displayed, with chart and graph views switching between a tabular report and trajectory graph. The next three affect what appears on the graphical displays removing/reinstating grid lines, causing velocity (or energy, wind drift etc) numerical values to appear alongside the graph line, and giving the facility to zoom into one section of the display. ‘Show normal trajectory' is a quick way of getting out of specialist displays/routines to return to normal results.

A small ‘window' that always displays five bullet descriptions appears on the main page, these descriptions being shorthand for load combinations. The software comes with five examples pre-installed. Before you do anything else, click on the ‘Load bullet' command to produce a series of drop-down menus to select a bullet from the package's database. With 26 makers listed it is large, although half a dozen of those named produce rimfire bullets, and is up-to-date, even including the new Berger 6.5mm 130gn Match VLD that importer Norman Clark has only just received from the USA. An instruction to select a slot appears above the display window during this process, allowing users to highlight one of the existing entries in order to overwrite it. If you miss this, as I did initially, the default selection is the top line. This means one automatically loses the previous input, which makes load combination comparisons impossible as well as increasing your workload.

The other part of the data input is done via a vertical section on the left with alternate menus: MV, zero range, maximum range, incremental/intermediate distances, elevation angle, and sight height. Click on the ‘Environment' alternative to input altitude, temperature, humidity and more, plus the bit that particularly interests target shooters: wind strength and direction. Infinity also allows a separate vertical component to be put in. An ‘Accept values' button at the bottom of the input window saves these selections for the highlighted bullet and results are produced by clicking on ‘Load' at the bottom of the display. One can change the combination's values or environmental parameters at any time by highlighting the bullet and returning to the input windows. The range options are very flexible, accepting any maximum between one and 8,000yd (unless the combination is calculated as being incapable of reaching that distance which applies to most normal bullets); any zero distance and intermediate increment size, even a single yard if you want! This only applies to the ‘chart view' (tabular) output: the programme determines the vertical (distance) grid line values on the trajectory graph.

Outputs

Having selected bullet(s) and put in MV, maximum, intermediate and zero ranges, wind strength and a few other things, what do we get when we click ‘Load'? The initial output is a ‘chart view' display table with ranges shown in rows (low at the top) and velocity, energy, and bullet path values for each range in columns. The on-screen display has alternate rows highlighted in sierra green, which is omitted if you print the output. The bullet-velocity combination and environmental parameters are shown above and appear on a hard copy, so you don't have to write them on afterwards to remind yourself what the table is for. The speed of sound is calculated and shown and a line is also printed saying whether or not the bullet is supersonic at the maximum range. Vertical bullet path and wind drift are shown in both inches and MOA, so sight adjustment from one zero to another is simple. I used this facility before the Blair Atholl F Class meeting, having got a 600yd zero in perfect conditions the week before (Figure 6). The display said my 175gn Sierra MK at 2,600fps would need 22.2 MOA extra elevation for 1,000yd, which reassuringly gave me a near-identical turret setting to the one I'd ended up with on day one in the April Diggle round. (However, while most of the ferocious wind effect had been horizontal at that shoot, the wind was blowing partly downrange, suggesting that 22MOA might be a little inadequate - and that's exactly what sighting-in at Blair revealed.) One can change the table contents using various options in the ‘Trajectory' menu, changing MOA to sight clicks (1/8 to full MOA), a useful facility for iron-sight target shooters or those using scopes without target turrets.

Point-blank

Talking about sporting shooters, how does the PBR facility work? Load bullet, velocity, and range data as usual highlight the bullet in the display window and select ‘Operations' from the toolbar. There are two PBR options - for Infinity to calculate maximum PBR and the required zero, or for you to input the zero range. Let's see what it tells us about one of the increasingly popular 55gn 6mm bullets used by fox shooters. Even my little 6BR cartridge can easily give these tiny pills over 3,400fps MV, so let's try the 55gn Nosler Ballistic Tip at this velocity. If you're setting the zero distance Infinity asks for this in addition to the kill-zone diameter (in inches), so I put in 100 and three, the former being what many sporting shooters incorrectly think of as a proper sighting in distance and the latter what I'm told is appropriate for a fox. The result tells us this is a non-optimal zero distance and PBR is 184yd. The ‘Maximum PBR' option works as before but you're only asked now for kill-zone size. We're told to sight-in at 210yd for a PBR of 249 and are also given a standard trajectory table based on the zero (Figure seven). However, 210yd is a tricky distance for many people, so let's redo the first step now with 200yd, the new PBR being 237yd. (Alternatively, with Infinity being so flexible, re-input the trajectory requirements for 10yd range increments and a 210yd zero. The resulting table tells us bullet strike will be 0.33" high at 200yd, so sight-in a fraction over the aiming mark on the 200yd range.) In practical terms our hypothetical fox shooter can now take any shot out to 250yd at that sight setting, and examining the trajectory chart shows the bullet should strike 5½" low at 300yd, so holding just above the animal's back should give good bullet placement. Infinity also tells us the bullet is travelling at over 2,400fps at 300yd, producing 710ft/lb of terminal energy, so no problems here. However, a 10mph crosswind moves the little bullet nearly 9", so long shots in windy conditions become problematical with a 3" diameter ‘target'. Another facility in ‘Operations', uphill/downhill angle effects on our zero and trajectory, is useful for the sporting shooter who uses a regular hillside spot. This tells us a 20º slope will see the Ballistic Tip strike 0.4" high at 200yd - not enough to worry about but it will reduce the drop at 300 by a full inch so less hold-over will be required.

I'll conclude this look at the ballistics package next month by examining Infinity's trajectory graph facilities. There is the ability to allow comparisons between up to five load combinations including wind deflection as well as bullet path - a factor that can give a competitive edge to a long-range shooter's kit. This should also give a pointer to the F-T/R class question of the moment - how do the Steve Donaldson and Ian Dixon/Stuart Anselm approaches compare (210gn Berger VLD at 2,600fps MV v 155gn Scenar or VLD at just over 3,000fps)? Infinity Version 6.0 not only predicts wind effect, but also has a recoil calculator to see if the heavy bullet causes any significant increase in this factor. I'll cover some features only introduced with Version 6.0 - profiled winds (up to four segments) and tactical shooters' trajectory tables. On the downside of using PCs to make potentially expensive equipment choices, I'll look at the ‘GIGO' factor, given that all home ballistics packages are based on G1 Drag Curve BCs. This acronym stands for ‘Garbage in - garbage out' and appeared in the workplace a generation back alongside the first generation of computer-produced data. Although rarely heard now, such is our belief in the infallibility of these turbo-charged electronic abacuses I reckon it's as relevant as ever.