The combined IQ of the 2 posters above me is bordering that of my dog.
Your dog must have a very high IQ then, smart ass.
Abs glue is not made to bind the two parent materials together to hold pressure (even though like pvc cement, it does fuse them), while pvc cement on the other hand is. From what ive heard both cements work on either pipe effectively, and seeing as abs pipe is almost always used in combustion cannons (as it is prone to failure with pneumatics), which is a very low pressure environment, it doesn't really matter.
You said that youv'e tested it with oxy/mapp, thats fine and it shows the durability of ABS and its solvent welds, but it is rare for somone to try that with an ABS combustion cannon, or a PVC combustion cannon for that matter. Generaly its hairspray, propane or mapp. All of which generally do not produce a very high combustion pressure.
As you said, you should use the correct cement for its listed pipe, but it won't make a huge difference if you use PVC cement or ABS glue.
what are you using to ignite the fuel? I saw two screws on the chamber so im assuming a bbq ignitor.