I owned Model 1899 ser. number 225 for many years and fired it often with whatever .38 Special ammo. I hapened to have on hand, including G.I. ball ammo. Never had any problems. It was the higest ser. number Mod. 1899 gun I ever saw without any caliber stamping on the barrel, although Lee reports some higher numbers. It was about 50% original nickel (ugly!) but a tight shooter with a 6.5 in. barrel.
I worked with Chuck Suydam on some of his research for his book, cited above and he was a very thorough researcher. I remember extracting bullets and weighing the powder on various cartridges to determine the number of grains the powder weighed. If he said the original UMC .38 Special rounds had eighteen grains of black powder it was probably backed by his research. Chuck's library of research material and notes on the articles and books he wrote were donated to the Davis Museum in Claremore, OK. on his death. Researchers can access his material there in the Charles Suydam room. Ed.