Okay, first of all, you need a Longshot, and something you want to mount under it. Initially, I had a DTG on the bottom, epoxied in place.

It was extremely effective, saving my life in many a zombie attacks. But one of my deepest darkest desires, along with mounting a chainsaw to my LS, was to be able to take the gun off and run with a lighter gun. I went over latches, magnets, duct tape. Over time, I'd given up on the entire idea. But a trip to Meijers and an hour of walking down every aisle, looking for parts for random homemade guns a friend and I were working on, I found a simple answer. SO here we go...
Supplies:
LS
Undergun worth mounting
Cabinet latches, recommend 4
Plexiglass
JB weld
Dremel
Piano Wire
cable clip, if you can't find one, use the clasp on a USB drive lanyard.
Metal Keyring
first of all, start off by comparing the two guns you want to connect. I began with a DTG already mounted to the LS. Second, try to decide which direction forces are going to act upon the gun. the mounts have to be able to hold the gun in place, but also counter your motion. My initial attempt worked quite well until I started sprinting and cocking the Dtg at the same time.
Before I go into the build, I want to clarify the terms used below.
The Latch is a small metal box with a spring inside, held between two rotating levers. The levers are connected to wheels that will rotate around the clasp.
The Clasp is an all metal piece, mounting holes on both sides. It is shaped like a diamond standing on end. When the latch is pushed over it, the wheels will go around the widest section of the diamond shape and the spring will squeeze them along a skinnier part of the clasp.
to decide where to place the mounts, I pushed them together, them maneuvered them around the surface, looking for viable places where both mounting surfaces could reach plastic.
The first clasp goes at the far back, at the end of the DTG body. the two surfaces with screw holes must be bent so the diamond shape of the clasp is parallel to the latch on the LS. The latch does go over the seam of the LS, so care must be taken to remove the screws before taking the gun apart afterwards.

The second and third latches are mirror images of each other. They are mounted on what's left of the front handle. To strengthen them, I cut plexiglass and JB welded it in. They are opposite of the other two because the latch goes on the DTG, and the clasp on the LS.

The fourth is my personal favorite, and the backbone of the mount. The clasp is mounted inside the DTG, on one of the screw mounts. To mount it, the screw holes of the clasp must be bent around so they sit flush with each other. Then they have to be dremeled out so they fit around the screw mount.

If you've placed all four mounts accurately, then the screws themselves should be able to hold the guns together. To make sure they all sit in properly, I coated certain places in JB weld. The two latch sets along the sides of the guns, only mounted to one shell can be reinforced simply by coating the threads inside the LS. The latch on the gun can be held in by coating the heads and mounting surfaces in JB. The front doesn't need any sort of reinforcement since it's on an already strong mount. The back one has to be strengthened with JB by either putting JB on one of the screw threads.
Now that the physical mounting is done, the serious part starts. A removable gun would be useless unless the trigger cable could be removed. I left the original design in, and added a squeeze and pull connector. One end runs into the gun, going to either the LS trigger, or a separate ring trigger, the chocie is yours. The otehr end is tied onto the DTG trigger by way of fishing line. When finished, it should look something like this.

I cut the barrel off a Double shot, ripped it in half, and cut it too fit the area and make it look better cosmetically. One side isn't mounted so I can take pics of it.
If you've done it right, you should be able to unclip the trigger, then pull the gun off.
Now I already know some of you are goraning, calling this a less-than-spectacular mod. Honestly, I agree with you. I state this because the DTG is very effective, but it is only the beginning of the possibilites that can be placed there. I'm almost finished with an RF 20 setup for the bottom of the gun, using the same mounting points and trigger. After that, a shotgun foregrip, and just for fun, a foam chainsaw. Nearly any gun could be modified to fit these mounting points, creating a variety of attachments
I do agree this isn't as clean as an RIS rail on an M4 rifle, it is more adaptable to different designs of nerf guns.
Special thanks:
OfAllTheNerf
Dickie
PyroManaiakal22
Groove
One Man Clan
Forsaken_Angel_24
Please ask questions, I quite enjoy answering them.
Edited by Kalentar13, 17 December 2007 - 10:27 PM.