ADI has produced a unique advance in propellant technology with Trail Boss, a specialist powder designed primarily for reduced loads using lead bullets in pistol cartridges. But riflemen too, can benefit tremendously from using Trail Boss which offers superb versatility in bottleneck cartridges with reduced loads with lead and jacketed bullets.
Loading cast bullets has always been a sort of post graduate exercise in the art of reloading since there’s a number of pitfalls involved which can trap the unwary. Anyone can pick a jacketed-bullet load out of a manual, follow the recipe, and end up with a reload that will deliver at least acceptable results in his rifle or handgun. It’s not so cut and dried, however, with cast bullets. They seem to require a fair degree of knowhow, in addition to technical expertise, that is not possessed by the average handloader. It is only rarely that the rifleman shooting a bottleneck rimless cartridge or a belted magnum may want to drive a jacketed bullet at 1000 to 2000 fps to serve some special purpose such as taking small fur bearing animals without ruining their pelts.
A major problem that plagues this practice has always been the small charges of fast burning powders necessary to produce these lower velocities. Also, the smart handloader has to exercise some caution when substituting jacketed bullets for leaden ones at maximum levels. Jacketed bullets being harder and less malleable produce more pressure, and, usually lower velocities. Also, a small charge of a fast-burning powder can produce high pressure, even in a large-capacity case if warnings about maximum charges are ignored.
Reduced loads are great for informal target shooting and plinking since they have light recoil and muzzle blast. They provide a handy method of accustoming a youngster or a novice shooter to heavier recoil, without developing a serious flinch. Start them off with light loads until they develop confidence and familiarity with the rifle, before easing them into full-power hunting ammo.
Trail Boss represents a major breakthrough in assembling reduced loads because it does away with the necessity for using a filler between the reduced powder charge and the base of the bullet. The small charges of very fast pistol or shotgun powders traditionally used for reduced loads normally weigh from 6 grains in a standard case to 25 grains in a magnum. Consequently, this leaves a lot of empty space, allowing the powder to assume varying positions in the case and varying shapes from shot to shot. Mostly the charge is spread out thinly across the bottom of the case so that the primer flash hits a different surface area of the powder and at different angles from shot to shot, causing variations in ignition that play havoc with ballistic uniformity. In the early days we used cream of wheat, cornmeal or kapok as a filler to hold the powder charge in a uniform shape and uniform relationship to the primer, later we progressed to Dacron.
Thanks to ADI that is now all in the past and there’s no longer any need to use extremely small powder charges in large roomy cases or spend time filling the space between the powder charge and base of the bullet with an inert filler. Just as importantly Trail Boss does away with any chance of double- charging a case and possibly wrecking your firearm.
The use of Trail Boss for reduced loads solves all these problems and more! Having extremely low density a light charge of Trail Boss takes up more space than faster burning pistol and shotgun propellants. In fact, when charges of two powders weigh the same, the washer-like granules of Trail Boss take up twice as much space as Unique – a popular choice for lead bullet and reduced pistol loads and SR4759 in rifle loads. This bulkiness decreases the amount of space between the powder charge and the bullet base narrowing velocity spread which can only enhance accuracy.
Trail Boss is a single-base powder and granules are light grey in colour; specifications give them a diameter of 1.92mm, a thickness of .58mm, a perforation of .76mm, and a wall thickness of 0.5715mm. The granules resemble tiny washers or, if you’d rather mini-doughnuts. Bulk density is .328gn/cc, a seemingly ridiculous figure when compared to the .700 to .900+ figures we see in modern, slow-burning rifle powders – but ideal for its intended purpose. Its bulkiness becomes evident when you realize that ADI’s standard 500 gram canisters hold only 255 grams of Trail Boss, so the standard canister weighs 1.5kgs. The burning rate of Trail Boss is quicker than that of Unique, allowing a lighter charge to be used to give the same velocity. For example, in a Rossi carbine with 50cm barrel in .45 Colt, 5.6gn of Unique drives the 255gn lead bullet at 850fps; by comparison 5.5gn of Trail Boss produces the same velocity, but because it is less dense it takes up almost twice as much room in the case as Unique.
As well as delivering uniform ignition with light loads Trail Boss is also also less primer sensitive than some of the other fast powders used for reduced loads. A mention of primers may be helpful here. Most of the powders used in reduced loadings are fairly easy to ignite, thus it might seem that primer selection would be no more critical in cast-bullet loads than in full-power loads with jacketed bullets. But in the past I’ve found some reduced loads with lead bullets to be very finicky about primers. This phenomenon is unpredictable however, and calls for trying different primer makes and types in any load that shows promise, as part of the final fine-tuning of a particular recipe. This is especially true of any load that shows a tendency toward vertical stringing of groups. Trail Boss, at least in my initial experiments with it hasn’t given any indication of primer sensitivity, but owing to the inordinately low pressures generated, I’d recommend using Magnum primers to bring them up to a more reasonable level.
A lot of shooters want to load their Marlin 1895 45-70 and other old big-bore leverguns to the lowest possible velocity to compete in Western Action events. Trail Boss is a superior propellant for this purpose. Minimum velocities listed in the majority of reloading manuals for other medium-fast- propellants such as SR4759, AR2205, AR2207 and Reloder-7 seldom fall below 950 fps to 1160 fps. It would be unwise to try and lower velocities by using charges lighter than those marked minimum, since ignition can become erratic unless an inert filler is employed. Thanks to its greater bulk, Trail Boss can be reduced in charge weight until the velocity is 25-percent lower without having an adverse effect upon ignition.
According to Hodgdon’s data, 12gn grains of Trail Boss behind a 405gn cast LFP bullet develops an average velocity of 971 fps in .45-70 Trapdoor rifles without any ill effect upon either velocity spread or accuracy. There wasn’t as much of a reduction in my mate’s Winchester 94 Legendary Frontiersman in .38-55 where 7gn of Trail Boss turned up 911 fps versus the minimum listed 935 fps gained with 7 gn of Unique. While hunters won’t have much use for squib loads in these oldtimers, they will hold an attraction for Western Action shooters.
According to Hodgdon, it is impossible to overcharge any cartridge with Trail Boss, simply because it is impossible to get enough into the case to exceed maximum chamber pressures. This is an important safety feature since its low density practically precludes double charging, that is dropping two powder charges in a case without overflowing it – something not easy to miss seeing.
Hodgdon also says that accuracy suffers when using Trail Boss in compressed loads, and that the smallest groups will be gained with charges ranging from the listed minimum amounts to those that just fill the case to the base of the seated bullet. And while jacketed bullets can be used in handgun cartridges, velocity spread will be higher and accuracy not as good as when cast bullets of the proper diameter are used.
Hodgdon’s IMR website lists loads for high-intensity bottleneck rifle cartridges. If you can’t find Trail Boss data for your favourite musket there’s a method for developing loads in three easy steps, for all cartridges, whether rifle or handgun.
First: Find where the base of the bullet to be loaded is located in the case and make a mark on the outside of the case at this point. Then fill the case to that mark with Trail Boss, pour it into the scale pan and weigh. This is your maximum load. Pressures will be below the maximum allowed for this cartridge and perfectly safe to use.
Second: Take 70-percent of this powder charge weight (multiply the maximum load from step one by .7) and that will give you your starting load.
Third: Start from this beginning load and work up in .5 grain increments to your maximum charge in order to find the most accurate reduced load. This will come at somewhere between 70 and 100 percent density.
For example, a 30-06 case holds 21gn of Trail Boss and optimum accuracy with a 150gn bullet should come somewhere between 13.3 and 19 grains. Another example: the .300 WSM case holds 24.5 grains of Trail Boss so you will probably find the smallest groups will come somewhere between 16.3 and 23.3 grains. Because chamber pressure even with a 100 percent density load is well below the SAAMI maximum, any bullet in the common weight range for a particular cartridge can be used.
Muzzle velocities with special purpose “squib” loads in bottleneck cartridges which are designed to reduce the report range from around 1000fps to 1600 fps with pressures from 14,700 psi to 25,000 psi. Such loads may only be effective at short range, from 30 to 50 metres, but are usually surprisngly accurate. Squibs are suitable for shooting rabbits or foxes with your pet high-power.
A couple of things worth noting: squib loads often develop too little pressure to expand the brass case for good obturation, (especially Short Magnums), resulting in an accumulation of soot on the outside of the case and chamber walls. Chambers need a thorough cleaning before firing high-pressure loads after much shooting of squib loads.
Also, brass which has been used for squib loads should be kept separate from your other brass, and must never be used again for full-power loads. This is because the force of the firing pin blow in some rifles can drive the case into the chamber far enough so that the shoulder is set back slightly. The pressure of the squib is too low to firefrom the case again, and a rimless case may end up with excessive headspace, which could be dangerous at high pressures. Cases used with squib loads need only neck sizing as they don’t obturate the chamber very solidly.
Squib and reduced loads using Trail Boss extend the versatility of your rifle to previously undreamt of limits. A low-velocity load will allow you to use your big-game rifle on rabbits and predators. By simply adjusting the velocity somewhere in the range of 1200 to 1600fps you will be able to head shoot rabbits out to 100 metres.
A useful load for a .22-250 uses a maximum charge of 13gn of Trail Boss to drive the thin-jacketed Speer 55gn TNT at about 2000 fps. This recipe will handle rabbits and foxes at ranges of at least 150 metres. Previously, medium-capacity cases handled reduced loads best, but now the cavernous-cased magnums work equally as well with Trail Boss, much better than they did previously with other less bulky fast-burners.
Using Trail Boss for special purpose handloads, the sky’s the limit. Most such loadings work at low-to-medium pressure levels, which allows the handloader to get more creative and devise loads which are uniquely useful. Handloaders who have never assembled anything but loads intended to squeeze every last foot- second out of their reloads, now have a chance to explore even more interesting aspects of their hobby.
This article was first published in Sporting Shooter, March 2011.