Hi Willyjixx!
I've powder coated two shotguns as demonstration guns for my AR15-870 stock adapter project. It is important to note that there are many different types of materials the powder coating companies have at their disposal (ie: epoxy, polyester, nylon, etc) and I would do some serious homework in trying to understand the type of coating you are planning on using.
For my test guns, I used a polyester based powder coating and thus far have no issues with it other than they coated it a little off-spec in the thickness department of one gun (to the tune of about 0.010 inches of excess material that made putting the gun back together a bit of an adventure. It is now very tight and a pain in the a** to disassemble)
Since coating the guns, I have about 500 rounds through each; most of this in 4 to 7 round strings. Thus far, I've been pretty happy with the performance of the coating other than the one gun being fitted so tight.
I hope this helps...
BrobeeBiter