If you are motivated to go through the hoops,go for it!
Otherwise, consider donating the a non profit 2A group and claim the highest insurance market values on your tax deduction!
I am an IRS-credentialed Enrolled Agent. That is, I'm a professional tax preparer who has passed a series of exams and I am admitted to practice before the IRS. For a donation that large, he couldn't just use fair market value to determine the amount of his charitable contribution deduction. Any donation valued at over $5,000 requires an appraisal and the completion of IRS Form 8283.
Of course, that assumes he'll even be able to itemize deductions, which is going to be situationally dependent. If the OP is married and he and his spouse will both be 65 or greater and file a joint tax return, their standard deduction for Tax Year 2025 will be $33,200 ($30k for MFJ, $3,200 extra for both over 65). Assuming their house is paid off and there is no mortgage interest, and they max the $10k SALT cap, and they don't have medical expenses in excess of 7.5% of their AGI, he'd still have $23,200 of standard deduction before it would help to itemize. That $23,200 eats up A LOT of the value of those guns, so he wouldn't really get that much of a tax benefit for donating them. (That's just shy of an average $2,000 for each of the 12 guns he listed.) Even if he and his wife are in the highest tax bracket, which would surprise me, given that he appears to be a former/retired firefighter, that's only a tax savings of 37% of the appraised value exceeding the aforementioned $23,200.
Yeah, the charitable organization would benefit greatly from the donation, but the OP would not likely see a substantial tax benefit, if he saw any, at all.
He would likely be much better off contacting a local auction house, as others have mentioned, and letting them take a 10% cut of the final sale price from him and get themselves a 15% buyer's premium, as well. Assuming those 12 guns sell for an average of $1,500, that's a total sale price of $18,000, or $16,200 in the OP's pocket. Assuming they appraise at a similar amount and the OP's tax situation is remotely similar to what I outlined above, he would get ZERO tax benefit from donating them to charity.
Of course, if the OP did sell them, and did receive more for them than he paid, he would be required by tax law to report that amount as a gain on his tax return. Since the OP refers to them as a collection, it stands to reason the IRS would determine they are collectibles, and the gain would be taxed at 28%, the tax rate for any gain on the sale of collectibles held for a year or more. If he simply reported it as a long-term capital gain on the disposal of personal property, the tax rate would be either 0, 15, or 20%, depending on the OP's total income. If personal property is disposed of for less than the price paid to acquire it, the taxpayer doesn't get to take a loss on their return.