I've decided on a combustion type sniper rifle that can maybe travel at about 50m-100m or maybe even more.
Here's what my experiement is based on,its a M24 Sniper Rifle

Here's what my sniper rifle would look like,

As you can see,the design lacks of many parts.For example,the slot where i can load my ammo and little component that I lack of.What i worry of is the chamber area.During combustion I'm very afraid that the explosion might backfire into the tubes of the aerosol can which might cause another explosion.Is there anyway to avoid this?And how about the
mechanism of the aerosol can spray?
Notice the different between both the picture is the extra pump below,(maybe also tad differences in the structure).No its not a hybrid(what you call it).Its just a simple pump to provide air into the chamber.
I know this is a rough sketch and it lacks much infomation, thats why I'm here to plead to all the experienced spud gun-makers to aid me along the process of making this rifle.I accept all ideas and advices even if it changes my original plans and critism too, because of these i would learn as i build. Thanks =D