I came up with a different mount for my Duplins to eliminate the slippage. See attached. It works very well. If any one is interested I have one mount left- $50 + shipping. Adds ~5.5 oz.
You would need to drill a couple holes in the Duplin face plates to install it and the tube will mount in your stock rail using the Duplin T-Nuts.View attachment 980925
Iron308 that might work for someone that doesn't have Trex arms.