I’ve often wondered what the hole at the rear end of a 416 lower is for.
Without even bothering to google it, I’d assumed it was some kind of ‘Over The Beach’ drainage outlet. I was very happy with this explanation. Maybe the engineers at H&K had decided the M4 didn’t shed water fast enough after being immersed?
Turns out that in the RS, the hole houses a pin for the buffer retainer. Boring, I know. I preferred my nautical theory.
The Reptile House 