if they have to negotiate with a few fence-sitting congressmen and senators,
So somehow a single organization, the NRA, proposes a "voluntary" program that involves manufacturers and private business, without those businesses input?
If they're negotiating with the politicians, the politicians still have input. Which means in order to win them over from actual legislation the "voluntary" program, which now being unilaterally decided by an organization for an entire industry, would have to be equivalent to the proposed legislation. How is that a negotiation? That's just giving them what they want via a different avenue. Furthermore why would these same politicians agree to such a "voluntary" program if it could just be dumped afterwards since it has no force of law?
Additionally, if they were to reach some sort of consensus, what would prevent the politicians from turning around and proposing the standards as legislation? After all it has the NRA's stamp of approval since they agreed to those standards.
Suggestions such as yours are not only ridiculous and half baked but also short sighted and just the sort of incremental "compromise" the other side is looking for. Your suggestion is predicated on the idea that this "compromise" or "negotiation" will satisfy them and they won't come back for more.
The far better option is to express to representatives that any further restrictions is not only unwarranted but will ultimately prove ineffective. This expression can be done both by contacting the representatives directly and donating to organizations like the SAF and NRA-ILA, so that they have the funds to continue fighting and winning in the courts as they have been as of late.
It's great that we have organizations like the NRA lobbying for our interests, however to rely on them to convey what we the people want is a mistake. The politicians know what drum the NRA beats, but ultimately they are not accountable to the NRA, they are accountable to us the voters. It's far more important that they hear the message directly from us.