With a fairly focussed agenda, like the 2nd Amendment, it might be difficult to generate sufficient support and numbers to be effective.
Most successful political parties are broader-based, for such reasons.
Sometimes, Interest group orgs, like the Sierra Club can be more effective for their cause than political parties. The Enviros have gotten pretty much what they want, and until the Green party showed up, without their own, in-house party.
The other side of the coin is the Libertarian Party, which for years has had a broad based platform, but has struggled to even register Pres candidates in all 50 states, let alone have any real impact. IMHO, the Libertarians ought to follow the war-plan of the Enviros, and skip the party politics for the time being.
The NRA is following the interest-group road, which, given the circumstances, is probably the correct one. (Not that I agree with everything they do, mind you).