I just finished my prototype of a NF rifle. I call it a rifle since it has the barrel length and plunger size of a large rifle, even though it has a small pistol body. Here it is:
As you can see, the plunger tube has been replaced with a PETG tube that is twice as long as the stock one. Two NF plungers have been cut up and spliced together to make a very long rod. The regular spring has been replaced by a gigantic spring from McMaster, the same wire thickness as you would normally mod a NF with, but twice as long. This gives the plunger enough air capacity to operate with an 8" barrel. Here it is cocked:
The barrels are coupled, so I can easily change the barrel length or type. I also made a 3-barrel shotgun attachment, it functions quite well.
This is just a test model to make sure all the parts can take the force. I forgot to add padding to the plunger head, so it will probably explode soon. That's OK cause I've been planning on making a plunger rod and head from scratch anyway. Once I accomplish this I'll be able to turn any NF into one of these beasts, the only parts I need from the gun is the body and trigger mechanism. The next version will look as good as it works. I really want to add a foregrip, since it is really too powerful to hold like a pistol. Here are more pics for the hell of it. Check out the video here:
NiteFinder Rifle Video
You seem to know a lot about nite finders, so do you suggest a higher tension spring, or a stretched spring in the gun?