One of the very best resources is the NRA books of firearms disassembly.
I think these are now volumes 3 and 4, available from the NRA.
These are reprints of all the disassembly instructions from the American Rifleman magazine.
This is excellent basic instructions on many types of guns of all types.
Gun Digest Books also has a series of firearms disassembly large paperbacks with each book covering specific types of guns, such as one book on shotguns, one on rifles, etc.
Gun Digest also has a Book of Exploded Firearms drawings showing schematics on many guns.
Having an exploded schematic is a great aid.
Online there the Steve's Site that has online schematics and owner's manuals for many guns, and Biggerhammer has a lot, including US Field manuals.
page7a
page7b
Note the info at the top of the page on what username and password to use to get in:
Biggerhammer.net - Miscellaneous Firearms Technical and Training Manuals
Last, Brownell's has schematics on most civilian firearms:
Schematics/Factory Gun Parts Home | World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools - BROWNELLS
Usually, your most common guns to clean will be shotguns, .22 rifles, and some defense type pistols for people who just own one and don't do much with it.
Most people who are "into" guns do their own cleaning so you usually don't see the higher end firearms.
Depending on your clientele you'll see more hunting rifles and shotguns then anything else and most of those field strip easily.
If a customer wants a real deep clean you'll have to know a lot more and have some tools.
A possibility would be an ultrasonic cleaner for deep clean jobs along with a spray type lubricant to get into the spaces.
You have to be very careful with gun cleaning because parts WILL break or will already be defective, and of course, you'll be guilty of breaking it.
Customers will not accept scratched or dinged up guns no matter how clean you got it.
For tooling, you'll need quality stainless steel rods, good jag tips, and will need to buy brushes in bulk because they don't last long.
Buy solvent in the largest size possible and pick a good general purpose lubricant like CLP Breakfee that lubes and protects.
Buy it in quarts or even gallons.
For hand tools you'll need a Brownell's Master set of Magna-Tip gunsmith screwdrivers, a large handle and a "law enforcement" size handle.
You'll need a small plastic hammer and a small ball peen hammer, a GOOD set of pin punches, and a magnifier visor and bench light.
You'll need a good bench with an easily replaceable cover so you can replace it often. Rolls of brown packing paper work well.
Be constantly aware that many guns require special tools or holding fixtures to reassemble, so be able to identify those and NOT take them apart farther then basic field strip.
