In replacing the factory pistol grip on an M&P-10 with an Ergo, I had a little "hmmm" moment regarding the fact that the safety detent spring is retained by the pistol grip, unlike an AR-15. The factory grip has a shallow dimple for the spring; the Ergo grip does not, nor do any other AR-15 grips I have seen. I would have touched it with a drill bit, but the Ergo grip is made of rubber where that spring lines up. Nevertheless, I had very little trouble getting it reassembled, but now the safety selector requires quite a bit of force to operate. Could that tiny bit of dimple contributed to such a significant difference in spring force?

In a word, probably.

I used a Dremel on high speed to create a hole with no problem. Safety works perfectly and the grip captures the spring a bit ease in disassembly.