By the time of these hearings the Republicans were in charge. Representative McCollum was head of that committee or subcommittee. They were going to have experts from the NRA go over the guns to see if they really were converted. The Dems created a real fuss about that and the Republicans, as they always do, rolled over and played dead. They rescinded their offer to let the NRA experts check them.
I am basically certain in my own mind that they were all legal and the information leading to the raid was a complete fabrication.
My understanding is that the Davidians had some of those spring-loaded trigger guard attachments that would burst 3 or 4 rounds when twanged. At the time their legality was uncertain and they were being sold mail order and at gun shows.