I believe the NMLRA was first started by Walter Cline back in about 1932. If he didn't start it, he sure had a big hand in it. Walter was shooting and writing about MuzzleLoaders when most people thought they were just an old fashoned piece of junk (or worse).
The NMLRA has similarities to the NRA, but it has it differences.
While the NRA has a Lobby to Congress, the NMLRA does not.
IMO the reason for this is the NMLRA only has about 20,000 members so they cannot afford to do this type of activity.
The MuzzleBlasts magazine does have several pages devoted to keeping us informed about pending legislation, and Court Interpretations dealing with Black Powder and Muzzleloaders.
Both organizations establish the Rules for competition in their areas of interest.
Both hold National Shooting Competations and provide support for local clubs across America.
The MuzzleBlast magazine has something for everyone from shooting match results, rendevous locations/dates/photos, food, cloths, How To's and trouble shooting, articles on different guns each month, Hunting, and a lot of History. I have even seen several articles about Matchlocks and WheelLocks in it.
Some people take offense at their position but they also cover the In Lines in a impartial manner, neither favoring or cursing them.
More vendors/suppliers advertize in MuzzleBlasts than most folks know exist.
As was said by several others, the magazine is worth the $40 membership fee.
The fee also permits you to compete in their postal matches as well as their regular ones.
I have been a member of the NMLRA for over 10 years, and the NRA for 36 years and I rate them both excellent in their own special ways.
IMO anyone with a real interest in Muzzle Loadeing should join the NMLRA.