Well......... As far as I know, a 209 primer isn't a paint primer at all. It is an ignition source for the powder in a bullet. There are a few different types, 209 being one of the most common. They're most commonly used in shotgun shells, and black powder rifles.
Etch primer
reverse primer, going from stop to start codone
Small pistol small pistol primer
Yes, you can if you are sure you need to.
Primer can sometimes be sticky if it does not dry well or is put on too thick. In most cases where there is low humidity a primer should not be sticky.
A 209 is a 209 regardless of what it is used for.
There are none produced that I know of, a 209 primer would be over kill in a revolver due to the small chamber and lower amounts of powder.
Among muzzle loaders, caplocks and flintlocks do not use 209 primers.
Federal 209A primers are hotter than Federal 209 primers and are hotter than Winchester or Remmington or CCI 209 primers. To duplicate your load when substituting Federal 209A primers in place of any other 209 primer, use 1 grain less powder for like performance.
Question can never be answered as currently written.
Depends on what caliber you are comparing it to.
Both would work, however a standard 209 should be plenty, and a magnum primer runs the risk of blow-back that could damage you and or the gun.
209. Double check with a gunsmith.
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.
Depending on manufacturer and model of gun it would be a 209 shotgun primer for inline guns or a #11 for sidelock guns.
#11 cap originally but there are conversions for them to use larger 209 shotshell primers to ignit pellets better.
Yes and is very worth your while to install it...google Badger Ridge Remington 209 conversion kit. Badger Ridge has the best one, and has lots of blog pages and videos about it.