What temperature do you think is required?

What will you do about the chamber?  If you're adding suspenders to an a safe barrel profile, yet want to protect against catastrophic failure, then the zone of greatest pressure should also be covered.

There's another aspect about what you're trying to accomplish that requires consideration, and that is the failure mode of carbon (or glass) fibers.  These materials fail catastrophically by sudden fracture, so they should not be worked to strains anywhere near failure strain.  Ductile metals fail gracefully by yielding.

So, none of that answers your basic question.  If you consider high temperature something over about 180 to 200 degrees, then oven curing is necessary, and most likely a post cure to raise the glass transition temperature of the resin will be required.  When curing steel plus carbon/epoxy together at elevated temperatures, the difference in the coefficients of thermal expansion must be considered if the parts are to work together correctly.

I can add more, later, I have a meeting.  

The only resins that will allow you to get anywhere close to 800F are silicones.

800F is completely out of the range of every material for a matrix that I have access to use, including phenolics.  You simply can't get there with epoxys, polyesters, or vinyl esters.  The rest you can't process without a controllable oven and/or an autoclave.

If you're heating a gun barrel to 800F you have other problems, too, the basic strength of the barrel is severely compromised.  Keep it up long enough and the barrel will sag under its own weight.

800F is probably far too conservative unless you are trying something really unusual.

I expect you're probably stuck with epoxies and limited to short term temperatures less than 300F.  Cyanate ester and bismaleimide resins (the next step up) will get you to higher temps, but processing is nontrivial.

Even nominally room temp or low temp cure epoxies will benefit from a post cure cycle to improve the maximum temperature where they can operate.

Send an email if you want, I expect you know that there is no way to select materials without understanding the function of the machine.  In the mean time, you can go to Henkel NA - Hysol products where you will find lots of information, including brochures.

You might also find something here:  West System Epoxies.  It's been a long time since I used their products or looked at the products they sell, so I'm not up to date.