I will go forward and say this is one place where modern production techniques have massively improved.
I have some old 06 ammo in the green and white remington boxes, I bought them in about 1976. i only kept that rifle for a couple of years (it was a loaner from a roommates dad. When I moved the gun stayed behind.) That ammo was shot in a 700 rem, ADL, with a 3x9 weaver scope on it. Some twenty five years later, I bought another 30-06, having a closet full of other calibers and decided to shoot that old ammo. The new gun came with a box of new ammo in the gun case and had a very good 4-12 power scope on it. It too was a rem 700, from about 1999.
At the range I had one box of old one box of new ammo. I tried the new stuff first, I was getting .8 or so groups, all nice and tight, nickel to quarter sized groups. I finished the new ammo and start with the old, after having a dog and coke in the warming house. all of a sudden I am shooting 2 to 2.25 inch groups, WTH!?!!? I am shocked, I pack up and call it a day.
At home the next day, I clean that new barrel till it glows, I check every screw, every bolt, making sure every thing is just as it should.
The next weekend I am back at the range, I try my now spotless rifle, with all the screws and bolts torqued to specs with a torque wrench.
I load it with the old ammo, First shot is nearly six inches from zero. The next four are scattered around the bull but the spread is nearly 3 inches. I take a walk, "what have I bought" I wonder, the gun cools off.
Back at the line I use up the last of that box of old ammo I have opened, again 2.75 inch group. A sinking feeling wieghs me down.
The guy next to me is a friend, we talk, he listens, asks if he can shoot it, I say sure buy all i have is some 180 CT I was going to sight in, but why waste them in such a crappy rifle, He says three shots, thats all, I say fine.....I am pouting and hoping the world is feeling as sorry for me as I am for myself,.
His first three shots all touch, looking like the number 8o but touching....he says, "its not the gun its the shooter".... laughing I grin and sit back down and decide what the heck at $1.50 a shot they better be accurate and lo and behold, I punch what looks like a 45 cal hole in the paper....Darn this thing loves this expensive ammo.
I get home and start thinking about it, so I go to the shop and buy some new rem corelokt and some new federal premium and bring another box of the old green and white.
The result, the old ammo shoots 2.5 to three inch groups, the new ammo, all of it, shoots sub 1 inch groups when I do not pull them. I shoot good, it shoots good. but bring back a few shots of the old stuff, back to big groups.