Leave them free to blow off the discharge petition as a way for them to show their true colors, then nail them or praise them for the choice they make. Else they'll get the one signature and a grudge against them for the coercion.
This is really stupid on the part of the NRA.
The NRA does not exist to elect Republicans. They exist to fight for gun rights.
They are using their “scoring” to push legislation they want to pass. That’s the whole point of scoring, not to punish people, but in the end to get them to vote how you want them to vote.