For those who have not used surplus powders, they seem mysterious and somewhat scary. They come with little or no data, and say things like "burns like H335". What exactly does "Like" mean in this situation? How do you load a powder for which you have no data? How do you know your loads are within safe pressures? We rely on the powder companies to provide those answers when we buy canister grade powder but with surplus we now have to provide our own answers.
If you are going to use surplus powders, a chronograph should be considered required equipment. These tools give us the information needed to load surplus powders safely.
The most important things to remember when using any powder is that velocity cannot be increased without a commensurate increase in pressure and that no-one ever destroyed a firearm by assuming a powder was faster than it is.
Always assume the powder is the fastest thing it could be and you may produce loads that are low-velocity, but you wont create an over pressure load by accident. If the advice from the seller is "burns like H335", I start with starting charges for H322. If the load gets less velocity than a good reference manual lists for the same quantity of H322, I can then safely assume it is slower than H322 and start increasing charges until I get to H335 published minimums. I watch the charges used vs. the published data for H335 during the work up to see if I pass the velocity of a starting charge of H335 before I reach the starting charge weight for the same. If 49gr of my surplus produces the same velocity as 53gr of H335, my powder is faster than H335 in this application and using Max published loads for H335 could be disastrous as pressure will be higher. If I cannot reach published velocities with published charges, I can assume my powder is slower than H335 and that a slight increase above published charges for H335 will be required to reach the same velocity levels. I make no attempt to get more than the maximum published velocity for H335 as with higher velocity comes higher pressure.
There is no magic to using surplus powders and almost all canister grade powders began life as surplus so contrary to what some may say, there is nothing inherently more dangerous about using surplus powders. Less data means more effort by the handloader, but all else is the same, after all, powder is just nitrocellulose and nitroglycerin, no miracle ingredients involved.