Agree with Skipper. Artillery propellants are smokeless. The last guns to use black (or Brown powder) were used in the Spanish American War. Bag guns do have a pad of black on the base charge to help ignition of the propellent. The max range of a 175 gun was about 32,000 meters the 105 only about 10 to 12,000meters. No where near 20 miles. The latest long range projo for the 155 gets over 20 miles and is terminally guided.
Jerry Liles