The main thing to remember about IMR7383 is that it is a HIGH ENERGY PROPELLANT that goes by different rules of loading density than the canister propellants that we are normally used to. The powder was designed for a very narrow range of application and is virtually without flash. It was meant for the 50 caliber spotter round on the 105 recoilless gun and giving away the position of the weapon before the main gun is fired would jeopardize the wellfare of the crew. As soon as the 105mm cannon is fired (definitely not flashless), the crew leaves to avoid return fire. I have fired my .30-06 700 ADL at night and instead of getting blinded with a large bright muzzle flash like IMR4895 makes, all I saw was a faint dull red streak emanating from the muzzle.
While what causes the phenomenon is debated, it is generally understood that 7383 is very peaky when approaching its upper load limits, giving absolutely no warning that a high pressure excursion is about to happen. This cranky nature is a very unfortunate characteristic of this otherwise quite useful powder.
There are at least three lots of IMR7383 that I know of and their characteristic are all different, so what goes for one lot will not work for another and it is a good idea to start off conservatively using IMR4064 loading data. I use IMR4064 data myself and have had good results. Also, it is not the best cast bullet powder around, although I get reasonable results in my French 36 MAS with the 180-grain Lee. Since the French cartridge is practically identical to the 7.65 Argentine/Belgian Mauser, it should work just as well in that rifle/cartridge combination. With around 39 grains if IMR7383 it also works well using 140-grain .308 brass tracer jackets in the French and .308 Winchester cartridges.
I am not trying to discourage using IMR7383 by any means, just be careful.
(Written by Linstrum)
I will add to what Linstrum posted by saying that I have found 7383 to burn very dirty below the pressures it needs and that once you find a clean burning load, you have reached the sweet spot. Going beyond the point at which you get clean burn is begging for a pressure excursion and should not be done. 7383 is certainly a powder where too much of a good thing is a very bad thing. I also find that 7383 doesn't like empty space in the case with it nor does it like compression. Best loads are most commonly found between 85% fill and 105% case fill. Below 85% is often erratic and above 105% is usually asking for problems with pressure. It requires special care when loading so has been given a section of its own.
The data provided here was safe in the author's gun at the time it was produced. This in no way implies it is safe in any other gun or should be used. Always use caution and work up carefully. We take no responsibility for the use of any data found on these pages.