I like the way your boss thinks, 416 Barrett is the way to go. Seriously I would look towards a 7mm-08 and for a rifle that doesn't cost a lot but is a great gun look at savage., weatherby vanguard, howa 1500, or Remington model 7.. For a sling while carrying on walks I would look at claw slings, they are rubber so they don't slide around on your shoulder to much they grip the clothing. If you have any reason to sling the rifle across your body you may want something like the Viking tactical sling.
My boss has a wonderful sense of humor.
But he is usually not far away from his beloved 338, which is his favorite. But he is large, so I would guess in comparison of sizes my 7mm prc is huge compared to me, as his 338 would be to him. He shoots that 338 from the saddle like it was a 22. I knew that he was strong when we first met, but a few weeks into working for him I learned how strong. We were in a trench he had me dig with an excavator, putting in a drain pipe, and some rock, to help control water coming off the shop roof during rain storms. The trench was deeper than I am tall, and it was time to get out. I had on my coveralls, he grabbed me by the coveralls, and just sort of tossed me up and out of the trench we were in. To say that I was shocked by his strength would be an understatement. My father, brothers, and male friends in the city would regularly work out in a gym. My boss has never been to a gym, and has 10 times their strength. I used to hit the gym 5 days a week, and ran 4 days a week. Since moving here, I no longer go jogging or to a gym, and my strength and aerobic conditioning are much better than they were.
I had been here a few weeks, when my boss said throw those 4 semi truck tires into your company truck, and take them to Kal tire. Sounded simple enough, until I was trying to lift them into the box of my truck. Then he realized I needed help. He said watch out and tossed them up there like nothing. I have no idea what a semi tire and wheel combination weigh, but he made it look easy, and for me that was like mission impossible. This summer, I was asked to put 2 into my truck, and run them out to a driver who had 2 flats a couple hundred kms away. I loaded 2 tires on my own. Yes it was all I could do to load them, and I broke a good sweat, but was super proud of myself.
Grabbed a jack, tools, and off I went. Drove 2 hours, found him, together we changed them on the side of the road, and headed home. It made me aware of how much stronger I've become.