I've taken my howitzer out 5 times in the last 7 weeks. She has bounced along on a trailer behind my Jeep about 1500 miles, much of that in the rain. For two outings I have heeded Dan's advice and allowed a patina to begin developing. Other than the bore, I have just cleaned with automotive soaps.
I'm afraid I don't have re-enacting in my blood. I use a big plastic bucket filled with water and two mops from Wal-Mart as battlefield implements. The two are ideal sizes for the powder chamber and bore.
On the way to central Texas the cannon was clean and polished, and people would ask if it was real. On the way back, with a scorched vent and muzzle face, nobody asked that question.
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She likes eating "Bocce" balls which come in several sizes and are hard like billiard or bowling balls. Bocce sets that were originally more than $100 per set of eight were on clearance here, so I bought a total of 48 Bocce balls. They make excellent cannonballs, and are re-usable if you can find them. I've lost 9 of them. My uncle will probably find them while herding cattle.
I stopped by the Fort Davis National Historic Site and met their artillery ranger last weekend. I'm driving back for their Labor Day artillery demonstration next weekend. They still have an original mountain howitzer that they do not fire. I am hoping that the dry conditions have preserved an original carriage, but I won't know until I'm there. It is kept indoors. If it is original, I'll take many pics of the carriage.