I'm pretty darn "pro-gun" and I like the federal requirement for private parties to do a background check. Having been to a dozen gun shows or so, there's this mentality that if you can buy a gun, and have it's transfer totally undocumented, that you pulled one over on Uncle Sam. It's a weird group, that I don't fully understand, but I too have never witnessed a purchase at a gun show, that was not subjected to a background check, in the State of Oregon. Now if two dudes wander off to the parking lot, that's a different story. The dudes in the parking lot need to be covered under this.
Where the bill lost me, was in the transfer from family members. I inherited a couple pistols and a rifle from two grandfathers over the past 3 years. As a person who has already had a few background checks for firearm purchases, and is merely taking ownership of my grandfather's pistols, it seems laborious and unnecessary to run a check under those circumstances.
How you word that so that you don't have thousands of people buying guns off of their 8th step-cousin on their mother's uncle's brother's side, I do not know, but I'm highly in favor of standard background checks between two strangers/non-family members.
The addition I would like to see is a database that matches known gun owners with roommates or acquaintances that they live with, who have documented mental illness. There will be tons of folks that slip through the cracks, but the requirement for owners to keep their firearms secure, and accounted for, could be expanded. THAT may have done something to prevent the Newtown shooting, because nothing in the bill would have, despite proponents using Newtown as motivation.