If you have a NFA Firearms trust and live in Pennsylvania you should take the PA statute 2203 into consideration. In Pennsylvania and many other states a surviving spouse has a right to an elective share of the decedent’s estate. Generally these are around 1/3 but vary by state.
The elective share is designed to make sure that the surviving spouse is not disinherited from the spouse when they die. In PA the spouse is entitled to 1/3 of property owned by the decedent including property in a revocable trust.
It is possible to have your spouse waive their right in regards to a specific piece of property. For those of you creating Gun trusts where the spouse is not a co-owner or a beneficiary, it would be wise to have the spouse waive their right to that property so that the property is sure to pass to your intended beneficiary.
Even if you create your NFA gun trust prior to a marriage, you may consider having a future spouse waive their right to that property prior to or shortly after marriage to avoid potential problems in the future.