Re: Who can ask for papers?
To answer the the OP's original question, in Texas, any state, county, or local law enforcement officer and ATF agent have the authority to check your papers. This is because in Texas it is illegal to own a SBR or OAW, HOWEVER it is a DEFENSE to prosecution that your SBR/OAW was legally obtained. It is always an offense to posses them, but the court will more than likely dismiss/decline to prosecute if you have the right paperwork.
One thing some people here are forgetting, or maybe are unaware of, is that the states have the right to make laws that are more restrictive but not less restrictive than federal laws. I can only speak for Texas because I do not know the laws in other states.
I'm a Game Warden, and am also a state peace officer, which contrary to what MANY people believe means that I can enforce any state law. Yes I can stop someone for speeding, whether you think I can or not. Also ANY officer (state, county or local) can check your hunting license if you are hunting, whether you are committing a violation or not, even though our department is the ones that regulate hunting.
We just made it legal to hunt game animals with (legally obtained) suppressors. Now if I'm out patrolling and I come across someone hunting or target shooting with a suppressor, I'm going to go visit with them. If I find that they are hunting, I'm going to check them for the required licenses and paperwork. Me personally I will usually ask how the hunting is and if people are having any luck, and usually people end up asking me if I need to look at their hunting license. However if they do not volunteer to show me, I'm going to ask for it. This would include the paperwork that shows that you have obtained your suppressor legally. If told no, I would politely inform you that possession of the suppressor was illegal in the state of Texas, BUT that it is a defense (basically get out of jail free card) if you have your paperwork for it. If I get told to "Fuck Off" we are going to have problems. This is because I don't appreciate being told to "Fuck Off" anymore than anyone else in the world who is just doing their job. Remember it is still an offense to just posses it in here, this means I CAN take you to jail for it whether you have the paperwork or not. Same as I CAN take you to jail for speeding or almost any other offense (there are a couple that are strictly cite and release). Just because I CAN doesn't mean I WILL.
Personally, I'm not going to take anyone to jail unless I have to, but that option is nearly always there. I've never come across anyone in the field with a SBR or suppressor. When that situation does happen I will likely visit with the individual and get as much information about their particular weapon because these things interest me. At the end of the contact if it has not already come up I will probably ask "You do have all your paperwork for this don't you?" if the answer is yes, I may ask to see it and I may not, just depends on the situation. If you do not have it on you and have not given me a reason to believe that you obtained it illegally then I will more than likely tell you that if you will keep your paperwork with you it will probably save you some hassle if you get asked for it in the future. If you are a complete dick during the whole contact and have done nothing but be a pain in the ass, we'll go from there.
Just because an officer can ask for something doesn't always mean that they will walk up and demand it. Another thing to remember is, a lot of times the person being contacted sets the tone for the contact. If you are an ass, the contact has a greater chance of going south. If you are polite, the contact has a greater chance of going smoothly. There are law enforcement out there that are asses and can make any situation go poorly, however there are a far greater percentage that will be pleasant until the situation calls for being more aggressive. There are some people out there that ALWAYS have bad contacts with law enforcemetn because they are asses from the get go. I can't tell you how many times I have been yelled at while giving someone a break, that makes it awful hard to take it easy on them.
Some of you guys are WAY overreacting/over thinking this. I can tell you one thing though, if you are an ass from the get go the contact is not going to go well. Same goes for the other way, if the officer is an ass from the get go the contact is more than likely not going to go well. Also I am a state peace officer 24/7 while I am in the state of Texas, I can enforce laws while off duty. That said, I am going to call a uniformed/on duty officer to take care of any situations that do not require immediate action to prevent harm to others.
This all pertains to the laws in Texas and the way I personally handle contacts, not the laws of other states or how other officers handle contacts. I do not keep up with the laws in other states unless I have a personal reason to, and I cannot control how other officers act.
ETA: This post ended up way longer than I intended and if you have taken the time to read the whole thing (or this whole thread) you have way too much time on your hands