Quoted:
Your videos don't prove much. Just moving a stock slightly lower on the shoulder, or changing the way you're holding your shoulder or amount of tension you're putting on it could easily make what little difference is indicated.
One thing the videos do show clearly is the lack of anything being redirected to the rear out of the vents in the brake. No gas going backwards = no recoil reduction.
This. Not to crap on OP, I like the idea of the videos etc, but if you are gonna put up a comparison video to show the effectiveness of different brakes, there are huge flaws in your test. It is impossible for any shooter to brace themselves exactly the same for any two shots, so showing how far back and up the muzzle flips is as much an indicator of the shooter's reaction to the shot as it is anything else.
The scientific way to compare would be to measure the pounds of force exerted or some other quantifiable measurement that takes as many other elements out of the equation as possible. The videos really show no useable data for comparison at all. It would be like comparing two suppressors and declaring one "sounds" quieter...the right way to do it is to measure the decibels.
Back to the original concept tho, I'd agree that Delrin is going to fail, having worked with it before myself. But regardless, it just doesn't offer any real advantages over steel or other metals in this application. Not sure what the payoff will be other than to say you tried it. Nothing wrong with that tho.