I am a little bit of a 270 Winchester nut, and have reloaded Remington, Winchester, Federal and necked down G.I. -06 brass without negative results. I have a hundred Remington Nickel brass loaded with WW785, 140-grain Hornady BT, and WLP primers that are real keepers. 99% of my loads work fine with all three rifles. I have only one commercial load that did not provide good accuracy in my M760; it was WW 150-grain power point.
The WW load was not providing expected results so I decided to shoot up the four or five boxes I had for practice and the brass. That quickly came to a halt when I started to fire it in a Remington 700. It proved to be very accurate, but produced low velocities. I guess high velocity is not everything because it sure has racked up the Mule deer, and the remaining boxes are reserved for hunting. The down side is that I have a good supply of hunting ammunition and needed to load practice ammunition. I should note the velocity of factory Federal, and Hornady ammunition was also load. Remington ammunition met expectations.
I have been careful not to mix headstamps or brass with nickel when loading. But at the end of the day the identical charges of the same powder, primer, and bullet provide the same accuracy.
In my bolt action 300 Savage a maximum charge of IMR4064 pushing 165-grain Remington C-L, Hornady, and Nosler PT puts the bullets in the same tight group at 100-yards. Like you I seek accuracy out of my hunting load.
I hunt deer in difficult terrain, and deer are not taken over bait from a fixed positions. Deer are taken as they are found. One of my better shots was off hand at about 75-yards. I had been working two bucks for about a mile in steep brushy country when I spotted one of the bucks looking around a large pine at me. All I could see was his head and neck. It was take the shot or forget it. The crosshairs were steady on the neck, and I pulled the trigger. The buck was a bang flop; the second buck did not present a good shot, and was gone. Knowing the 270 shot a tight group was the deciding factor. I would have passed on the shot if I was carrying my British 303.
There was a point years ago that the accuracy of known rounds dropped off. I was in a surge of reloading and shooting. A 200-yard walk and I could shoot my rifle a few rounds before work. I would shoot a few rounds, quickly clean the rifle and get ready for work. The downside was I was getting the powder residue, but not all the copper residue. More attention to the copper residue resolved the problem.
The copper issue has been around a long time. This past Saturday I had two family members loading at my bench. I had them bring their rifles to make sure the resized cases would chamber in their rifles. Their rifles had nice shinny bores but by looking down the muzzle end with a light on the side I found copper in the bores. One cleaned bores while the other one loaded.