TECH TALK Update on Obatex
BA CK IN OCTOBER 2019, Magnum publishe d a pi ece entitled ‘Puzzling out our Propellants’, which covered the problems experienced by shooters of old time weapons when substituting new locally made black powders for the overseas imports that are no longer available.
One of the observations made in the article was that the locally made Obatex powders produced more energy per grain weight than other more traditional black powders. This is acceptable in a muzzle-loader as the charge and bullet seating can be adjusted to suit the smaller powder volume in the chamber, but gives problems in loading black powder cartridges as the lesser charge leaves an air space in the shoulder and neck of the case which needs fillers, all of which adds to the variables involved in getting these old cartridge rifles to shoot to their sights at longer ranges.
The other concern was that an inexperienced shooter might just fill the case to capacity which might be permissible with a traditional black powder but could result in a serious overload with the higher energy Obatex.
THE GOOD NEWS is that we have had a call from Hannes Van Wyk at Obatex who told us that his latest production (December 2019 ) generated less energy per grain to bring it closer to the traditional black powders which results in a much safer and user-friendly product.
To get a useful comparison between the old and new powders we re-did some tests using last year’s results as a baseline. These tests were made using the No 2 Musket cartridge as a standard because it fitted into the gap between the .45-70 US Government cartridge (which has a lot of American data for comparison), and the larger capacity Martini Henry .577/.450 cartridge which is common in South Africa.
The desirable condition for shooting any black powder cartridge is a full case of powder lightly compressed, to give a muzzle velocity in the region of 1 200 to 1 250fps with a 480gr bullet, as per the original factory round.
For clarity, the results from the new style Obatex tests in 1½Fg and 2Fg granulations have been kept separate in two charts. The cases were tapped lightly to settle the powder to avoid any
subsequent air spaces. For the lesser charges, a filler of mealie meal, lightly compressed, was used (as recommended by Hannes) and seemed to work well, though please refer to remarks about Standard Deviations in velocity.
OBATEX 1½Fg RESULTS
Since a charge of 44 grains of old style powder produced velocities near our 1 200fps, the same charge using the new style powder was tried to get the difference. With 1½Fg granulation this gave 1 149.0fps, which is 3% less. The charges were increased progressively and we found that 53gr gave us 1 275.5fps which was slightly higher than we needed but nevertheless confirmed that a greater bulk of powder was needed to reach these desired velocities, which is a sensible safety condition.
As a final test we went to maximum we could get into the case, which was 62 grains with slight compression, giving a velocity of 1 394.1fps, which is higher than any factory load we could find (1 350fps). However, while the recoil seemed heavy, the Bertram cases ejected easily although the primers had flattened showing that significant pressures were present. Since this was the maximum we could load we concluded that the powder was well suited to the case.
One useful outcome of the test was that the Standard Deviations in velocity of around the mid-30s came down to the 20s and under, showing that Obatex works much better with more compression and less filler in a fuller case.
OBATEX 2Fg RESULTS
Similar results were obtained from the 2Fg test. The velocity drop for the 44gr charge was more pronounced at 12%. Proportionally increasing the load to 48gr only produced 1 097.4fps and it took 57gr to get up to our desired 1 243.9fps. The maximum load turned out to be 65gr giving us 1 339.3fps, which compares with factory loads. Once again, recoil at the maximum load was heavy and primers were flattened but the cases ejected easily. It was also noticeable that the Standard Deviations with the 2Fg matched those of the 1½Fg tests in being much improved with the bulkier powder.
The bottom line of these tests is that the latest batch of Obatex has shown to be a much better match to the cases used and indeed, with a few more adjustments, we may say that it can reproduce the original factory loads which is exactly what we need.
SAFETY NOTE: Although the new style Obatex is now bulkier than the previous production, it is still not as dense as the traditional black powders. For that reason, it is still NOT SAFE to use the VOLUME measures that many black powder shooters have, because these volume measures are calibrated for other powders like Wano. As a rough guide, 65gr of Obatex 2Fg occupies the same VOLUME as 105gr Wano, so the traditional volume measures just don’t work here.
Measure your Obatex charges by weight until your standard reliable load is reached and only then start to think about a volume measure specially made for your Obatex charge.
The other safety note is that shooters are advised to clearly mark their tins as to which style of powder they have. Loads developed with the new style may well prove disastrous if the older type is used inadvertently.