What are Federal and State restrictions on paintball guns?

Anything over 500 feet per second is considered a firearm. As most markers max out (engineering wise) at about 360 fps, you should be fine. Paintball guns are not required to have an orange tip on their barrel (thank God) even though a good number of the markers out there today look like the real thing.

You will need to look at mechanism patents. Many of the marker manufacturers have multiple patents either confirmed or pending on the operation of their markers. Autococker's bolt forward system and Smart Parts, shuttle valve being just two of many. Of course, much of these patents can be licensed for use.

I personally think that Smart Part's spool valve is engineering genius, when it comes to mass, speed and cycling time. A lot of people dis the Ion internals but I've rocked more than a few games with my little stock marker.

As far as PSI restrictions, your limited by ASME ratings on the pressure vessels. A standard 48cui Steel tank is rated for 3000psi, that pressure is stepped down to around 100 psi in most markers. Of course this varies from marker to marker. As far as CO2 goes, you've got to allow for expansion of gas within the marker and have a fail safety point in regards to the O-Rings. Tippmann products might be used mostly with HPA these days but their markers are still made to take CO2, even in liquid form. Something that will kill damn near every electro.

Here in Canada, were restricted by CSA standards, which are a crock for the most part. If you're in the US of course you'll be dealing with UL certification. One work around is to use pre certified components in a body of your manufacture. This will allow you to jump a lot of the expensive testing for certification process if you ever want to go into production.

Good luck.

Honestly...not much restriction at all, at least not on the State and Federal level. Field owners, Sanctioning bodies (PSP, XPL, etc,,,) and players themselves have set the muzzle velocity limit to sub 300FPS, and firing rate caps vary within different game types. Other than that, i've never seen an "illegal" Paintball Marker.

I do not have the answer to your question, but rather some sound advice.

Gun laws are very complex and vary greatly from state to state. Before you invest any significant amount of time or money into your project, be sure to hire a good attorney to advise you.