The story behind this review of Gamebore Dark Storm Precision Steel 32g with Bio-Wad cartridges

In previous reports on new steel shot offerings from UK cartridge companies, I have explained the difficult position cartridge makers have been put into. Here we have a fresh example of how a leading UK manufacturer has tackled the uplift from standard steel cartridges – for those guns that are not steel-shot proof-tested and marked – to the ‘Formula One’ division of high performance (HP) cartridges. Cartridges designed to comply with the HP specifications, as designated by the CIP, and have higher velocity and momentum limits to work with.

HP 12-bore loads have a velocity ceiling of 430 metres per second (m/sec); just 5m/sec higher than for standard steel. In reality, this is a small increase. Shotgun cartridge velocities are more difficult to maintain within the tight limits that quality rimfire or centrefire cartridges achieve. It’s not at all uncommon for velocities to vary by rather more than +/- 5m/sec, which makes it difficult to take full advantage of the modest uplift. Note too that these CIP limits are already considered by some manufacturers to be on the conservative side.

The momentum uplift is useful. It permits a heavier shot load to be used along with the velocity as high as the manufacturer dares within all the imposed limits. It is pointless to be too adventurous by working right up to the limit on velocity because, in theory at least, there is no upward leeway with specified CIP velocity; it is up to and including 430m/sec, but no more.

I like to think that the proof authorities might take a pragmatic approach in the event of any unintended minimal transgressions but, technically, current rules mean there is a risk of a batch failing proof if they are found to digress. Given the vast outlay in load and component development costs cartridge companies continue to endure, it is clearly a potentially expensive risk to sail too closely to the CIP limits and risk having a batch rejected at proof. (Read will my gun be safe with steel shot cartridges?)

Latest version

The cartridges reviewed are the latest version of the Gamebore Dark Storm Precision Steel 32g with Bio-Wad cartridges. The wad used is the new Mk 2 brown and water-soluble Bio-Wad. The earlier Mk 1 Bio-Wad was green in colour and was withdrawn shortly after reaching the market. It helps understand the difficulties and pressure that cartridge companies are enduring at this crucial time of change, when a company of this size and experience has to rethink a major component so soon after its launch. The challenges are, quite simply, immense. There should be no cartridges with the Mk 1 wad still on sale; if you find any at a dealer, do ask for the Mk 2.

It is interesting that Gamebore has now chosen the water-soluble route for its biodegradable wad. Thoughts on which material will prove best over the long term remain in the balance. Some companies have changed to compostable from water-soluble wads. Water-soluble wads are compostable too but the non-water soluble compostable type take significantly longer to break down. This Bio-Wad weighs 67 grains, which is around 24% more than a similar HDPE (high-density polyethylene) steel-shot wad.

Success will, to some extent, depend upon how landowners over whose land we shoot react to how long wads remain visible – be that on land used for clay or game shooting. The problem is finding suitable biopolymer materials that are of sufficient mechanical strength under heat, pressure and rapid acceleration during the journey from chamber to muzzle and also capable of resisting steel pellets from pushing through the shot cup to prevent barrel bore contact.

This is a very tall order, especially when the biopolymer must also be suitable for high-speed precision moulding. HDPE plastics were discovered in the early years of oil-based plastic research and development and were found to be exceptionally strong, flexible and well suited to the production of plastic wads.

The propellant in these Dark Storm cartridges is a square, black, cut flake powder that visually appears to be a grade of Maxam SSB, a successful range of powders designed for use with steel shot ammunition. Propellant charges averaged 27.3 grains. The burn was fairly clean but some fine dusty streaks were visible in the bore. I am happy with that because the pressures are modest for the velocity achieved.

Shot size

These Dark Storm Precision Steel cartridges are marked “high performance” (as required by the CIP) and so the CIP shot size limit goes up to 4mm. The shot size printed on these cartridges, and on the carton top flap, is No 3. However, note that the actual diameter printed on the carton is 3.5 mm. This is not UK size No 3 (which is 3.3mm). Measuring 10 pellets with a micrometre showed this sample of shot is slightly larger and measured an average of 0.14in (3.55mm). This is not a problem because it is well within the CIP shot size limit.

It does, however, mean that there will be fewer pellets in each cartridge. This has the advantage of higher individual pellet energy for better penetration and energy transfer at greater range. The other side of the equation is pattern density across the useful spread; the eternal ballistic conundrum that we will all have grappled with at some point. I refer to this as the shooting man’s ‘Question of Balance’, only this is not the Moody Blues reflecting on life and love, but pellet energy versus pattern density. T

These cartridges therefore comply with CIP HP steel cartridge proof requirements. Again we find the breech pressure is actually within the limit of 740 bar for standard steel. As I have previously mentioned and, contrary to a common misunderstanding, breech pressures are not the issue with steel shot cartridges that many seem to think. This proof report once again confirms the great versatility of modern propellants, which are able to produce all the velocity required and within CIP pressure limits.

As ever it is actually momentum that potentially creates the most problems for cartridge makers. I mentioned in the previous steel cartridge review that the proof authorities and the Gun Trade Association (GTA) have published advice regarding chamber length and cartridges. While we all know not to use cartridges longer than our gun’s chamber length, it has long been assumed that using shorter cases, even if not ideal, is at least safe. This topic is under review by the GTA and its members plus the British Proof Authorities.

Early indications suggest that some guns have suffered damage to their forcing cones when using steel shot cartridges of shorter case length than the chamber from which they were fired. It could be some time before we have any solid report and potentially advice but, for now, matching the steel shot cartridges to your gun’s chamber length is the advice.

This may become awkward for some, given that over the past 15 years or so a high proportion of new guns have been produced with 76mm (3in) chambers as standard. This is often the case even though 70mm ammunition is probably used the most. For many seeking a new gun during that time, the longer chamber seemed a good idea as it made the gun more versatile. Hopefully, as we learn more about which circumstances cause some guns to suffer, when using shorter steel shot cartridges than the chamber length, it will be possible to obtain cartridges that help minimise any such risk.

The CIP maximum momentum of 13.5 Newton seconds (Ns) for 70mm 12-bore cartridges becomes a factor. Note that although these cartridges are comfortably within the CIP velocity limit, the momentum result is still very close. Getting very close to the allowed velocity limit of 430m/sec would exceed the permitted momentum figure. The velocity SD (consistency) figure is good at just six. This translates to a spread of 22m/sec; it also shows why some margin must be left even when SD is held to low single figures.

Patterns

A key point with all the steel shot cartridges I test now is: how close to full choke will the patterns be? I use a 1/2 choke Beretta Mobilchoke as these are very popular and 1/2 choke is the recommended maximum for HP steel shot cartridges. Gamebore prints on the cartridge carton that HP cartridges containing shot larger than 3.25mm “must strictly be used with a MAXIMUM choke of half (.5mm) or less”. The gun must also carry the fleur-de-lys steel shot proof symbol.

The proof of pattern performance is revealed on the pattern plate and these proved quite consistent. Five of six patterns held a total average count in the 30in circle with just 20 pellets’ difference. Only one fell eight pellets less. These would be very small differences with the higher pellet count of smaller shot sizes but a 28 spread with a total count of 174 pellets per cartridge is quite a bit.

Pattern percentage averaged 65%; this equates to a ¾ or improved modified (imp mod) pattern density and therefore still short of a full choke (70%) pattern at 40 yards from a 1/2 (modified) choke.

As an experiment I also repeated the pattern test with a very modern gun with longer and highly developed chokes, wondering if the 1/2 choke would produce the magic 70% result. Sadly the answer is ‘no’ and the average result was 5% less. This proved once again that you will only ever know how your gun and cartridges pattern by testing for yourself.

We are all having to relearn what we know about shot sizes, patterns and especially our comfortable and humane shooting abilities.

Meanwhile, the basis for the ‘full from 1/2 choke’ mantra we have so often heard appears ever-more elusive. What we can see from the pattern results is that at 40 yards the coverage across the pattern, even with 65% pattern density, is approaching the limit of reliably achieving sufficient strikes at range. Although some shooters are accomplished shots when tackling game at ranges in excess of 40 yards, it is clear that the 50-yard-plus birds require very careful consideration. Respect for quarry must remain paramount even if that means saluting that ‘archangel’ cock bird without raising your gun.

Many claims will be made, for sure, but results so far lead to a degree of caution if we are to maintain our reputation for sportsmanship. If that should be lost all will soon follow.

Tests I intend on conducting more pattern tests with other choke types. I shall also try the new choke that performed below the Mobil but using a tighter constriction to see if that improves the pattern density. These chokes are expressly described as suitable for use with steel shot up to full choke.

As I have noted before, recoil can feel sharp with steel shot loads. Momentum is higher than a similar lead shot load making this all but inevitable; these cartridges will certainly be more comfortable used in a heavier over-and-under.

These are high-quality cartridges that make the case for larger shot sizes with greater energy per pellet. How they will perform in the field, where patterns can often fail before pellet energy – even with lead shot if stretched too far – can only be judged in the field. But please do your homework before venturing forth.

Performance statistics

• Configuration Gamebore Black Gold Dark Storm HP Precision Steel 70mm 32g No 3 Bio-Wad
• Shot load 496 grains
• Pellet (count/lead) 174
• UK shot size (actual) No 1 (3.55mm)
• Pellets in 30in dia (Av) 112
• Pellets in 20in to 30in 50
• Pattern 64.5%
• CD 55%
• Velocity 408m/sec (1,339 fps)
• SD 6
• Recoil 13.07Ns
• Pressure 733 bar

Test standards