Hello Frank,
No, there was a vast difference in pistol powder and cannon powder. I am far from being an expert, but as one who was an Army reenactor for some years, I have of course extensivly used small arms powder and have seen cannon powder, at least for army field pieces. I don't know if you shoot much Black Powder weapons, but if I remember correcly the powder for small arms, pistols and muskets, is about like the size of sugar granules (pistol powder being a bit finer than musket powder). The cannon powder is vastly different and much more bulkier, where each grain is the size of an English Pea or something like that.

Now that is for say the average Army field piece such as 6-12 Pounder smooth bore or rifled guns (6-12 pdr smoothbores like the 12pdr Napolean Smoothbore, the 3"-4" Ordnance Rifles, 10 pdr and 20pdr Parrot Rifles, etc., etc.).

Now, as I said, I am no expert, but for the huge 7"-15" Siege, Naval and Sea Coast guns there might even be a larger grain powder for them. I am not sure if the mobile 30pdr Parrot Rifle, which is mainly a large army field piece-siege gun, would fit into this catagory. Perhaps someone here with more knowledge than my scant bit might expound on this subject. You might try the Artillery in the Civil War board ( http://history-sites.net/mb/cw/cwartmb/ )for answers to these questions about powder.
Take care,
Dave Edelen
Millbrook, Al.