The recoil thing is a project that was regularly a student experiment feature and well documented. Won't go into it again but some of the notes were repeated on an earlier thread several years ago. To register how little effect the operating gasses venting via the gas port make you can just rotate the gas plug to shut them off and it barely registers

The T-piece is rivetted through the cover and the reinforced open square section as I seem to remember it. Just re-rivet I say, with red-hot steel rivets. When they cool and contract..... there ain't a lot of recoil going to pull them apart!

We used to have a few No78(?) telescopic sight for the ill fated L1A1 'marksman' rifle and they were mounted on that tinny top cover and open square reinforced part too and suffered the same fate