Mike: Welcome to the forum. Take Heed to what McKeal has written above.
As to buying the " right " powder for your new, 1851 Replica Revolver, you should be looking for a " PISTOL " powder. In Real Black Powder, you are generally going to use Goex Black Powder in FFFg granulation. In a rare case, some guns shoot better using Goex FFg powder.
There are different granulations or sizes of granules of Black Powder, and since the mid 19th century, they have been designated by the " F" system.
Fg is considered suitable for use in cannons. Its the most coarse granule size sold by Goex.( The small "g" after the F indicates the powder is coated in graphite- used to eliminate the possible firing of the powder by static electricity. )
FFg is considered Suitable for use in Rifles, shotguns and large bore pistols.
FFFg is considered suitable for use in revolvers and small bore pistols, and is also used often in many rifles. As the Granule size goes smaller, the rate at which the powder burns increases, so that FFFg will generate more Pressure than does FFg in a given caliber.
FFFFg is suitable for use ONLY as a Priming powder for Flintlocks.
The industry makes even finer grades of black powder= 7Fg for firecrackers, for instance-- but sale of these items are limited. ( 7Fg powder was also sold to Photographers to use, before electric lights came into being, for Flash lighting of their subjects to take pictures. It was dangerous, as the powder burns so fast, and was burned openly, so that when too much of the powder was used( very often), any flammable item near the flash could be ignited. If you see the movie " Butch Cassidy and the Sundance Kid", the photographer who takes the pictures of the two western crooks uses this kind of flash powder to light up the pictures. )
Swiss Powder has its own grading system, for its powder.
When you turn to the substitute, or replica( Synthetic) powders, like Pyrodex, and Triple Seven, or Pinnacle, each company that makes and markets these products has its own recommendation for which powder should be used in revolvers. Pyrodex, made by Hodgdon Powder Co., designates its pistol powder as " Pyrodex P ". Pyrodex powder for Rifles and Shotguns is designated as "Pyrodex RS".
If you are going to buy any synthetic powder- ie, NOT BLACK POWDER-- then you MUST READ carefully the information on the packaging as to what the manufacturer says it should be used for shooting. DON'T GET YOUR INFORMATION FROM DISCOUNT STORE CLERKS! If you have any questions, come back here and ask.
As to buying Black Powder, few retail outlets still carry it, simply because of the New( since 9/11) requirements for storage imposed by Homeland Security, on top of State Regulations. The kicker for most retailers is that it has to be stored at least 300 feet from residential properties. That eliminates most " strip mall" stores.
Under member resources here, on the index page to this forum, you will find a section titled, " Articles, Charts, and Links". "LINKS" is computer talk for fast ways to find other sites of use for you. If you click on "links", you get a list of suppliers and dealers in Traditional , pre-1865 products, divided into sections to make it easier for you to go to the area of interest. Under " Powder", you find a list of names of manufacturers, and suppliers. Click On GOEX( or do an engine search for GOEX) The site has a map of the United States, with flags to indicate the location of distributors of their products around the country. Find a GOEX distributor closest to you, and click on that name. You will get the address and name of the company, and, usually, a toll free phone number to call. Call the company ( distributor) and ask them for the name of the closest retail store that sells black powder. If there is NO close retailer, the distributor will be happy to arrange to sell and deliver to you the powder you need.
Now, all Black Powder, and percussion caps, are subject to a " Haz Mat( hazardous materials) Fee, that is charged for each shipment of powder in interstate commerce. The Current fee is apparently $22.50 per shipment. It only makes sense to join with other BP shooters, who also have to find ways to acquire BLACK Powder, and caps) to order a larger shipment of powder, than what you might use in a year, for instance, so that the Haz Mat fee is divided over more pounds of powder, lowering the cost of shipping. NO?
There are often state restrictions on how much powder YOU can possess, unless you also meet certain state requirements regarding storage. OBEY ALL LAWS. You can lose your right to own and possess all firearms if you don't! This limitation controls how much powder you can possess, but not how much you can buy, or have shipped to you.
Federal Regulations limit you to receiving no more than 2 cases- 50 lbs. of powder per single shipment. That would be 50- 1 lb. cans or bottles of powder( Bulk powder sold in plastic bags also is available from some sources. With this, you would have to divide the bulk powder into your own containers for local storage.--ie., SAVE YOUR OLD POWDER CANS!)
Case prices are usually the cheapest way to buy Black Powder and represent a considerable savings.
The only way to pay less, is to travel to the distributor's business, and buy your powder directly from him, so YOU transport the powder home, and you will not be charged the Haz Mat fee.
With the price of gasoline, having it shipped to your house would normally be cheaper. However, if you happen to have another reason for driving past or near the location of a distributor, then buying the powder direct does makes sense.
If you find a local shooting range or club, for black powder shooters- check the Charter Clubs listed by the National Muzzle Loading Rifle Association( NMLRA)-- you will find other shooters with whom to join together to buy case lots of Black Powder.
My gun club has done this annually for more than 30 years as a service to its members. Orders are taken, and checks made out to the club treasurer. When he has enough orders to order a case of powder, the order is placed. When the shipment arrives at his home, he calls members who have ordered the powder and they go to his home to pick up their orders. If the money they paid is not enough, or was too much, the matter is settled with the Treasurer when the powder is picked up, with many members simply leaving extra money with him to help pay for their next order of powder.