The problem of generating significantly reduced velocities from large capacity rifle cartridges - the problem of the CAS shooters, or plinking with heavy iron.
There is an other end to this spectrum: the desire to shoot bullets, reliably,
accurately, and slowly. Today's CAS shooter has no interest in max'ing out
45-70 loads; and likewise, the 416 Rem Mag owner would like to plink/learn the
trigger, with far less than lion stopping loads. Today this topic is said to
be poorly understood.
There is an other end to this spectrum: the desire to shoot bullets, reliably, accurately, and slowly. Today's CAS shooter has no interest in max'ing out 45-70 loads; and likewise, the 416 Rem Mag owner would like to plink/learn the trigger, with far less than lion stopping loads. Today this topic is said to be poorly understood.
Most hand loaders of today are used to and their experience is with (rifle) loading recipes involving high load density charges. Almost all of today's standard reloading manuals talk of loads which are in the load density ranges of 80-85% to 100% plus (compressed loads) - and implicitly espouse the view that velocity is a linear function of charge weight, ie, if one wants the maximum velocity, one loads the maximum listed charge weight, and if one wants less than the maximum, then one loads proportionally less powder.
As long as one is interpolating between the listed starting and maximum loads, this is a safe view - or at least one with which one is not going to get hurt. The unfortunate leap is when handloaders try to extrapolate below the listed starting load, in search of reduced velocity loads, especially ones involving less than 60% charges.
Powders designed to ignite in a high pressure environment quite often ignite unreliably, if at all, or even detonate in a low pressure, low load density, context. (One can observe this with the slower rifle powders listed in the 45-70 Gov engineering data on this site.)
If one wants a motorcycle, one does not get there by multiply successively slimming down an automobile - a new paradigm is necessary.
A Problem with an Old Solution...
Question: have the laws of physics or thermodynamics changed within the last 100 years or so? No. Question: if in the past there were loads, which even though they had low load densities, were known as target loads and shot in the velocity range sought by the CAS shooters and plinkers, might something be learned from studying history? This author would suggest: yes.
The following observations are base on data from: The Ideal Reloading Manuals, #29, #32, #36 (1929, 1936 and 1944, respectively); Lyman #39 (1953); and Phil Sharpe's Complete Guide to Handloading (1937).
Working definition: "pistol powder" is any powder with a Relative Quickness (RQ) of 180 or greater (ie, faster), assuming IMR 4350 is defined as RQ 100. IMR 4227 has a RQ of 180.
Interpreting the Old Data
Gallery Rifle #75 (introduced 1904, discontinued 1928) a fast pistol powder, maybe on par with today's vvN330 or vvN340. Described by Sharpe as: a bulk powder... fine-grained, fibrous in structure, irregular in size and shape... screened through 26-to-the-inch mesh and caught by 60-to-the-inch mesh... development was strictly to give the military reduced or target loads suitable for ranges up to 200 yards.
Sport Rifle #80 (introduced in 1913, discontinued late 1940's), again a bulk fibrous powder, irregular in form, screened through 24/inch mesh, caught by 56/inch mesh - slightly more coarse than GR75, and somewhat slower burning, maybe on par with today's vvN350.
Of the double base powders, they were of two forms: short fine tubes, like or finer than today's IMR4198; or they were disc powders; but never a ball powder. The double base powders were: Unique, by far most often; and in decreasing frequency of mention: HiVel #3, HiVel #2, Lightning, Sharpshooter and #2400.
Unique (introduced 1900, still produced today), initially produced by Laflin & Rand, absorbed by Du Pont in 1902, given to Hercules in the 1914 anti-trust settlement. By Sharpe's words: one of the best of the entire Hercules line for mid-range use in the military rifle family or the so-called Sporting Rifle type such as 30/30, 3855 etc... one of the most useful and flexible powder a reloader can have available. A disc powder (.060" diam x .005" thick). RQ is 300.
HiVel #3 (introduced 1926, discontinued 1960's), a tubular powder, .080" long x .035 in diam (IMR4198 is .085 x .025). Sharpe has to say: superbly accurate and flexible... in the 300 Savage a charge as low as 10 gr can be used... developing a velocity of 1180 fs and a pressure too low to register. A RQ of 200, like 2400.
HiVel #2 (introduced 1914, discontinued 1960's), the only other tubular powder on our short list, a slightly larger grained powder (.085 x .040), and hence somewhat slower version of HV3. Again according to Sharpe: in the 300 Savage the same bullet [167 gr GasCheck] with 15 gr is given a velocity of 1100 fps.
Lightning, actually, Lightning #1 (introduced 1899, discontinued 1950's, different from Lightning #2 which came and went, 1903 and 1929), a disc powder, .080" diam x .020 thick, a RQ of 160, or that of IMR4198. Like Unique, developed by Laflin & Rand, taken over by Du Pont 1902, and given to Hercules 1914. Sharpe has to say: an excellent mid-range powder... is extremely accurate, requires a low weight of charge to develop velocities.
Sharpshooter (#1), introduced 1897, discontinued 1940's. (Different from Sharpshooter #2 which came and went, 1902 and 1914, respectively.) Another disc powder, .080 x .015. Quoting Sharpe: designed for use in the 45/70 Gov cartridge... very easy to ignite and extremely accurate in performance... can be used in loads so very light in rifles that they can hardly be measured on a pressure gauge... it is an excellent mid-range and reduced powder for any of the bottle-neck types of cartridges, regardless of caliber. A RQ of 260, between Unique at 300 and #2400 at 200.
#2400, introduced 1932, still produced today. A disc powder, .030 x .015. To quote Sharpe: is one of the most flexible powders in the Hercules line... data listed in this book list the use of #2400 in more than 30 different cartridges... it can even be used with the 220 gr (30-06) bullet, 14 gr giving a velocity of 1180. A RQ of 200.
Listening to Sharpe's comments, the use of these low load density loads, was not only not blowing up guns, but is was producing excellent results: accuracy, consistency.
More Recent Data
If one accepts that internal ballistics is not magic, but good engineering, then the fact that RCBS settled on powders which are characteristically the same as those used to perform the same tasks, but used in the early part of the 20th century should not be a surprise. In decreasing order of use: Unique, Red Dot, 700X, Green Dot.
Du Pont 700X, introduced 1968, still produced today, a disc powder, double base (.057 x .006), RQ of 635, very fast, pistol powder, very clean.
Red Dot, introduced 1932, still produced today, a disc powder (.060 x .003), double base, RQ near 360, a fast pistol powder.
Green Dot, introduced 1965, still produced today, a disc powder (.060 x .005), double base, RQ near 300, a fast-medium pistol powder.
Conjecture 1) powders ignite in one of two ways, conductive ignition and convective (or flash) ignition. Where conductive ignition is defined as most of the energy required to raise any grain of powder to its kindling point (temperature of ignition) is via low impedance paths offered by physical grain to grain contact. This is how one grain ignites the next grain of, eg, IMR 4831. This is an artifact of the heavy deterrent coatings, high internal thermal conductivity and large thermal mass and hence sink each grain represents.
Convective ignition is where no physical contact (and hence no conduction) is required, but where each grain is bathed in hot ambient gases (from the primer or from other grains burning), and due to its small thermal mass the entire grain is raised to its kindling point whereupon all its surfaces spontaneously ignite. This is how all the double base disc powders burn. Flash ignition is a special form of convective ignition, where the entire powder charge begins burning simultaneously.
Conjecture 2) the heavy inclusion of nitroglycerine in the disc powder's formulation is no accident. Nitroglycerine when ignited generates significantly hotter and more gases than nitrocellulose. If this were not true then as the charge weights increased one would begin seeing coked, unburnt residues, which one does not see. The initial hot nitroglycerine gas comes almost immediately after the primer flash and supplements the primer in igniting all other grains.
Conjecture 3) the disc shape is not accidental. For the powder charge to ignite uniformly and consistently each grain must be bathed in hot gases and must not be sheltered from such by other grains. The thin disc shape acts as a sail and causes upon primer firing the charge to resemble a colloidally suspended solution: hot gas and powder particulates.
A corollary to this is that for a powder to be viable in said application, it must not be packable. This is why ball powders are unsuitable - a wavy edged disc with high sail area to mass is not packable in the context of a stream of hot primer gases. Pliable low sail area to mass grains are more inclined to be compacted against the base of the bullet and smolder, generating non-ignition, partial ignition, and either way very non-uniform ignition.
Another corollary to this is: if the sail area to mass ratio is great enough, then independent of the orientation of the cartridge and hence the location of the charge within the cartridge, upon primer discharge, one still ends up with a reasonably uniform mix of primer gases and powder particulates, ie, loads which behave the same muzzle up, muzzle down or muzzle level.
New Data, More Testing
Apparently like most other handloaders searching for lower CAS class velocities, this author started with reduced loads of standard 45-70 type powders: only to find, like everyone else, copious unburnt powder, and unstable velocities. He then tried, again apparently like most others: somewhat reduced loads, but with slower than standard powders, again to find unusable results. Switching to magnum primers didn't help.
Then came the ahha: trying something that hadn't been done before (or at least as far as this author knew at the time), but wholly made sense intellectually: what would happen if one were to switch to a light load of a fast, trivial to light powder? Would the bullet lodge in the barrel for insufficient pressure? Shouldn't - where would the huge pressure drop come from if one burned a 44 Rem Mag max load in a case with an extra 30 gr of freespace - one could imagine a 50% reduction, but enough of a reduction to lodge a bullet - seemed unlikely. Could the load detonate and blow up the gun and/or gunner? Again seemed unlikely - where would the extra energy come from, given that one picks a powder which ignites given the slightest encouragement from a primer, and in this case, also moving from a large pistol (not even magnum) to a large rifle primer? There comes a time when theory has to become practice...
Noting that the 444 Marlin was both built heavier (as a firearm) and with brass significantly heavier than the 45-70, the first and fateful experiment was conducted with, a 240 gr SWCL, sitting on 10 gr of 700X, in a 444 case. The first round was loaded, the hammer was dropped, and it felt like shooting a 44 Special from a 1894. There was a hole in the target. Nine shots later, after each checking primers for any signs, and checking the bore for a lodged bullet... Instead of lodging bullets in barrels, or blowing up the gun and/or gunner, what was seen was a 4" group, at a velocity under 1100 fps, and with an extreme spread in velocity of less than 15 fps. Progress had been made.
The next trip to the range was with more 444's loaded with other, similar (or at least as perceived by the author) pistol powders: more small groups at low velocities with low extreme spreads where shot. More progress had been made. These new powders where: the old disc Accurate #5, Blue Dot, Unique and W231.
At this point a fortuitous rereading of Sharpe and the discovery of "pistol powder" loads for large capacity cartridges added confidence the author's pistol powder discoveries.
Since that time this author has shot several/multiple thousands of pistol powder motivated rifle loads. The data for the original 444 Marlin ah-ha data is available on this web-site. Subsequent 45-70 data has also been added to the web-site. 30-30 Win, 35 Rem data will be added soon. 25-35 and others to be added later.
What was Observed
The energy available to flash ignite a powder charge is: that amount of energy supplied by the discharging primer, minus that energy used to heat the other components of the system: the cartridge case, the bullet, the receiver of the gun etc. This heat loss is determined by the components of the system, and is unique to each system.
The amount of energy required to flash ignite the powder charge is greater than the simple: total residual energy (primer energy minus system heat loss) required is equal to the number of grains times the energy required to ignite each grain. After primer discharge, the primer gases are reasonably uniformly distributed within the case. If the powder flakes were also uniformly distributed, then the above statement would be the exact minimum energy required to ignite the system. But the powder flakes, sailing in the turbulence of the primer gases are not uniformly distributed.
By definition: if flash ignition is to occur, then independent of the powder distribution, there must be local to each grain to be ignited, sufficient energy to flash ignite that grain, ie, if there are local powder densities which run n times the average across the cartridge space, then there must be n times the energy value given above, integrated across the combustion space to still guarantee a flash ignition. Any energy level less than that results in ragged conductive ignition.
The lower "ignitablity" limit we encountered has to do with: in general, as powders become slower, the energy required to light each grain increases. Since a primer, case, bullet etc system will only have so much residual energy, the number of grains ignitable with that energy decreases. As the number of grains decreases, the amount of gas generated decreases and necessarily the muzzle velocity decreases, and at some point, to a value less than sought or usable.
Although RQ and energy required to ignore do not exactly track each other, a rough guide we've used is to exclude powders with a RQ of less than 200 (the RQ of 2400).
Of Note: a failed flash ignition, becomes a ragged conductive ignition, also known as Detonation. Extreme care must be exercised with loads near the flash ignition, ragged conductive ignition border. Detonation is a life threatening event.
gj mushial, 12 jul 99
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