The ‘flange’ is this
The stock rail disassembles in the following way
1. Unload and clear the gun.
2. Separate the two halves by pushing out the ‘take down pins’.
3. Push down on the charging handle latch and remove the charging handle.
4. Remove the BCG from the rear of the upper receiver.
5. Depress the gas plug detent and rotate the gas plug until the top and bottom tabs line up with the cutout on the gas tube.
6. Remove the gas plug and piston assembly.
7. Using the folding stock lock tab, push down on the bottom half of the quad rail.
8. Separate the top and bottom quad rail by lift up at the rear and pulling out.
Note – you can either remove the gas tube or leave it in place, the stock rails will disassemble either way. In the pictures I have it unlocked as I was in the process of cleaning. Yes, even gas piston guns needs to be cleaned
The Samson rail installs by removing your stock hand guards and the top rail mounted on the receiver. The top rail of the Samson is then installed in it’s place and the bottom secured to the top.