Roger on the Gunny. His early weapons were not the same as came later. Early on he was shooting a Winchester 70 heavy barrel in 30-06, after that he got a Remington 700 in 7.62X51(it later morphed into the M40). The MC was buying rifles off the shelf and doing field modifications. The special purpose weapons came later (M14, M40,). One of the things he taught me (and anyone who was interested) was that even though the .308 was more accurate than the 06, the reason was uneven ignition as the 06 had an extra half inch for the propellant to slop around in whereas the .308/6.62X51 had a more tightly packed charge due to its shorter length, the field expedient solution if one wanted the extra 40-50 meters from the 06 was to make sure that the round was held parallel to the ground and tapped so the powder charge would level out inside the case and give more uniform ignition, then load it carefully into the chamber, the difference may have slight but when you were shooting at real sniper ranges it mattered. I once asked the gunny a question about whether some thing mattered or not, he looked at me and said "Kid, everything matters". The Marines let me use their training range from time to time, and after they realized I was really interested , I got lots of good info. Their boss was a Captain whose name I forget, once remarked "Don't spend too much time around here, you might forget how to fly". I told him "NFW, that's my job", he just grinned. Told me he might be able to get me into the Corps as an E-2 when my hitch was up (I was a CWO2 by then). Told him if he could make it E-3 I might consider it, got another grin out of it. Don't regret not being a Marine, probably would have been dead for the last half century or so. But the USMC has my everlasting respect, some of them kind of liked me too when I showed up in my CH 47 to pull some of them out of a tight spot. It carried lots more people/cargo than the Navy/MC CH 46 Sea Knight, and was a lot faster too.
I'll still stick with my M1, and modified FAL, make me feel secure. My M1 ammo now has filler to take up that extra space and keep the burn uniform. Its dark and rainy right now, maybe I'll go load up some ammo.
BTW, you are absolutely correct about the new weapons coming down the line. However I am going to stick with what I know, and can shoot. In any case at my age I don't think I can see anything at 1500 meters, much less hit it. Although if I get real tired of what I have now maybe...............