With all the huge variety of powders which are available to us today, people lose sight of one point: military ammunition generally used the fastest powder they could get away with. Reason for this was cost, of course, as all powders cost about the same to make. A charge of 40 grains will be cheaper than a charge of 50 grains. As well, there was shipping tonnage to consider when supplying troops in the field. An extra 10 grains of powder in each of 3 million rounds is almost another 4300 pounds to be freighted up to the front..... and, at one time, it all had to be hauled by horses, mules or men. A couple of tons can make rather a difference when you have to carry it several miles.
And so the military loads generally were made up to suit the quicker powders. It is possible to squeeze more power out of them with more-progressive powders NOW, but these were not available a century ago. They were only just beginning to become available HALF a century ago. So rifles designed 117 years ago (such as the Swede M-96 and its family)....... or 123 years ago (the whole .303 clan) were engineered for what they had at that time, which were what we now call the faster powders.
AG-42/42B were engineered for existing ammunition, in this case the Skr. Patr. M.39 with the 139-grain spitzer-type FMJBT bullet..... and it had a relatively-fast powder. Fastest way to get into trouble with this rifle is to start loading with slow powders. Stick to mild loads with something like 3031 or 4895 (at slowest) and bring the loads up until the rifle is ejecting in a sensible fashion: not tossing its empties halfway to Saskatoon.
Hope this helps.
Have fun! That's what it's all about!
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