Parker did not differentiate between fluid and Damascus steel for load recommendations. For 12ga , Parker published light, medium and heavy load recommendations, the heavy being stout indeed. There were load recommendations for 16, 20 and 28ga as well. Velocity is provided on the following table so while drams equivalent is stated only for DuPont smokeless, it can be roughly determined for other powders. Note the statement about where velocity is measured.
Another way of loading is to use the patterning load that Parker used for your specific gun. If you are missing the hang tag for your gun, what would have been on it can generally be determined. The predominate Parker 12ga patterning load is 3 dre 1 1/8oz, which has been the standard trap load for over 100 years.
Service and proof load pressures, both mean and maximum, are provided in a Parker table in The Parker Story. They generally follow SAAMI standards of the day. I do not know of any hammerless Parkers that were restricted to shoot less than SAAMI service loads when SAAMI standards were established or previously, industry norms before SAAMI was formed.
While loading down may be a general good practice and many people have their own ideas, sometimes owners want to know what the designer and manufacturer of the gun recommended.
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