I figured if I was getting into 5.7 guns I might as well get out of the shallow end. Just picked up from my transfer dealer.
Probably 5 years ago I had just put together a 7.62 x 39 AR pistol. I must have gotten a little comfortable shooting it and relaxed my stance a bit when the buffer tube smacked me in the lips! I learned my lesson and went with the sling in the arrangement that you're describing. I also put a rubber barbell sleeve on the buffer tube just in case that happened again. No blood was drawn and my teeth were left intact, but I took the hint.I just adjusted the sling to use around the shoulder in a push configuration so I have a good sight picture and the back of the gun doesn't hit me in the face.