I've posted this information here before but since it has been two years or more since the last time and the blackpowder mortar/cannon forum has many new members since then it may be time to mention again that the Company of Military Historians Forum has a lot of information on artillery, here:
http://www.military-historians.org/cmh/member/member.cgi You can search back about ten years through some 12,000 topics to find short articles or Q/A on cannons, artillery ammo, artillery accouterments, reference material, etc.
Each page of the forum contains only 2 months of topics, so if you have to use the control at the bottom of the page to look back further, but the "search" feature will find your topic of choice quickly if you set the timeframe longer than the default "2 months."