Your inexpensive powder has deteriorated, and most who say use it for lawn fertilizer, are prudent and correct...it's not worth good bullets and primers to shoot..fact. But...if you have cast bullets or cheap old factory bullets and low to moderate velocity loads for your IMR4198 are very common. It can be used...I remove most of the red rust colored dust, by using compressed air while slowly pouring the powder out of 1 pound can and into a large cardboard box, while a moderate force from the air compressor blows the rust away. Load to a low or moderate velocity and it shoots pretty good. Ran a few pounds of IMR 4350 I purchased for $3.89 a pound new out of the store, through the 338 Win Mag 200 gr Speer new old box $5.18 per 50 bullets and CCI 200 primers $8.90 per thousand...down to about 1500 of those at that price. Assembled all the outdated components, and went to the range. They ran like normal the velocity 2700 fps on the low side, but fun plinking and able to take any game animal in the state. I believe some content is lost in the dust and the powder is lighter by volume now than when first manufactured...so that the charge weights should remain low. Old geezers, and folks outside the norms of society don't throw nothin out, but find a way to use it. I ran 8 lbs of Free Ireco 85 through the 50BMG with no clue except it was a slow powder...it was old no data but it was free...turned in some nice groups at moderate velocities.