Requests for realistic guns of all types have always been a really popular request on the forums and on the front page comments, so I thought I would try to finally answer one of the biggest groups of specific requests and try to make a large sniper rifle prop for cheap! 

I find it helpful to try to start with a toy gun as a base, the molding and detail you can get on a lot of toy guns are simply hard to replicate cheaply and will save you a lot of time. 

Next, take a PVC tube, the one I got was around an inch in circumfrence, so kind of thin, but thick enough to look like the barrel of a big anti-material rifle. I then marked off a section of the tube about arms length, and then cut it off.

Next, I took a wooden dowel that fits well in both the tube and the barrel of the toy gun...

And I epoxied it into place inside the PVC tube. With this particular model of toy gun it's plenty stable without having to put the epoxy in the gun barrel as well, meaning it doesn't make the toy inoperable, but it fits snuggly enough as to not bounce around when running or anything like that. 

With no real support it fits snuggly in, and stays in place well. Depending on the model of toy gun you get, you may have to adjust the size of the dowel and tube, or epoxy it in place permanently, or even drill a proper sized hole to fit, it all depends on your needs.

Now, for the vents on the end of the barrel. I took some cardboard and cut out sections to make a box. The two big ones are the top and bottom, and the two smaller ones are the sizes with vents cut into them. The front and back aren't shown, but should be the same length as the top and bottom, and the same height as the side vent pieces. 

I hot glued the top and sides together first...

Then follow with the back and front. With the front I poked my X-Acto knife in and twisted it into a circle, then to smooth out the ridges I stuck a dowel through it and slide it in and out until it was smooth, and then squished a little hot glue on it and smoothed it out some more with the hot glue gun tip. Then I poked a hole in the back and stuck a piece of dowel into it, which I then epoxied onto the end of the "barrel". 

Now, it's just a matter of the paint job! Go with the typical paint job for machines, start with a primer of grey or silver, then go over it with black, and distress and wear on edges to make it look old. Or don't do that, and go over it with a layer of clear lacquor to give it that "new and fresh from the factory" look. 

From here on how you customize it is up to you, stencil on serial numbers, crew ensignias, kill-score card scratches, tripods, and telescoping sights, etc. whatever you feel suits the character or setting.

Quick tip, a great thing to use for a shooting tripod would probably be one of those mini-tripods that you can find in the electronics sections of most big-box stores, just screw it near the end of the barrel and prop it up when your actor is "shooting". Wouldn't look super-authentic (unless you're shooting a sci-fi film and can modify your gun however you want), but it'd be some extra flair that might work for your film. 

Good luck! Post any questions or suggestions down below!