It should be a #11 cap. Comes in tins of 100 available from CCI, Remington and many others.
Depending on manufacturer and model of gun it would be a 209 shotgun primer for inline guns or a #11 for sidelock guns.
Size 10 or size 11 percussion caps, which are still available today at any big sporting goods store.
Small pistol small pistol primer
15 amp
By 870 I assume you mean the Model 870 shotgun? If so, there would be no purpose for that type of conversion. Shotshell primers are of the 209 size. The 209 "conversion" is done with muzzle loaders. The idea is to replace the muzzle loader nipple (that holds the cap) with a conversion unit that uses the 209 shotshell primer to get more positive ignition of the black powder.
a.69 cal
Depending on the manufacturer, either Size 10 or 11.
Small rifle
SOME ammo can be reloaded. Not all can be. A fired cartridge case is cleaned, and the old primer removed. The case is lubed, and pushed into a sizing die that squeezes the brass back to it's original shape and size. A new primer is seated in the primer pocket, and a measured charge of powder poured into the case. A new bullet is pushed into the case mouth, seated to the correct depth, and may be crimped in place.
if u are asking if u can shoot it yes u can
It depends on the size of container you buy. The average size baking powder container sold is 8.1 oz (230g) that size has a little more than 47 teaspoons.
It varies depending on the particle size of the powder.