Adapting the Adaption:
This adaption bracket, shown here, should NOT be used to support a gun mount. It is NOT designed to handle the recoil pressure from the firing of a weapon. Please look at the Universal Chair Mount.
In 2008 I got a new wheelchair. The legs on the chair rise out to 90 degrees. The first year we had many problems with the brackets which secure the legs to the chair. They would twist and break. The manufacturer said the brackets are designed to twist out of shape in order to protect the much more expensive legs from being damaged. We had to replace the legs three times in the first year. After the third time we moved the legs up and back closer to the seat to give them more stability. It worked! However, it created another problem. The Alternative Bracket we put on the chair would not sit level because the pivot point of the legs stuck up higher than the seat pan. We decided it would be necessary to cut out part of the original ABS plastic, from the mount, to allow the piece to drop over the hinges of the legs and lie flat. Unfortunately, this weakened it quite a bit. After some unsuccessful attempts to strengthen and stabilize the plastic we realized it was time to come up with something new. You must be ready to modify equipment when it no longer works for you. Changes call for other changes.
A close friend of mine and I brainstormed for a new method. Geoff is quite handy and has made other equipment for me. In the winter he works for the local highway department and so had some old highway signs. The signs are made of one-eight inch thick aluminum which is quite strong. He took a piece and made the bracket below. The metal just sits on the pan of the chair underneath the cushion. One of the advantages of this is it can be easily removed. If your chair seat is totally flat there is no reason to cut the pan. The application of this adaption is even easier. It cost nothing to make and works just fine.