Perhaps velocity of the projectile gong through the powder plays a part there. Back in the late 70's, a bloke in Terrace B.C., having a sporting good store, was in possession of several pounds of (Scotish)ICI FG. that he seemingly couldn't sell. IT sat on the shelf for years as no one would shoot it in their rifles as it was just too coarse, even for ctg. guns. The grains were HUGE rounded chunks of powder, more similar to what used to be pictured as canon grade than any rifle grade of powder. I have shot off lots of 1F or FG GOEX and the GOEX FG is barely 1/10 the size of this ICI stuff. I still have a bit of it, but it is low energy powder. IN my .58 Hawken, it took 200gr. to match the velocity of 150gr. 2F. The velocity was the same, but the 200gr. FG kicked more.
: Anyway, that's the background - he shot off some 8 lbs. of the stuff using his 7mm Rem with 120gr. handloads at 3,700fps, at the 100 yards line, For every shot, he got a large poof of white smoke. I do believe he shot the cans on-end through the steel lids. The sides of ICI cans are paper.
: I did not see this, but was told of it by him and he indicated the 7mm mag set them off by the bullet going through the can of powder. According to this thread, this isn't possible which is interesting as he had no reason to lie. When visiting Terrace on ahunting trip, I stopped in and asked him for BP. He said he'd only had ICIFG but he'd shot it all off - then laughed. I asked him what was funny, and he told me HOW & WHY he'd shot it off - with his 7mm Rem. At the time, in Smithers B.C., I had used it in my 50 3-1/4" Sharps at 170gr. per charge with 550 gr.RCBS bullets & the 45/70 at 80gr. IT was also more dense than GOEX powder.(more dense = heavier for same volume)