All your questions have been good.
I reload for only one .280 Rem and that is my SIL's 700 Rem DBM
When we went gun shopping with his tax return money a few years back that rifle stood out at the local gun show and I bought dies and new brass at the show.
I ordered a few hundred Hornady 154 gr. SST bullets and built a batch just to test starting below the max as listed in my Third Edition Hornady manual.
My loading for this was,
52.9 grains of IMR 4350
154gr. Spire Pt (SST bullets yet to be developed)
This first test firing was at 100 yd with a junk drawer scope ( Bushnell Sportview 3-9 that I had removed and replaced with a Leopoldo Vari X III 2-8 on my 77 Ruger .270 Win.
My SIL put 3 rounds all cutting the same hole and did that twice. It was my turn and I confess I had never shot a 100 yd group like that with anything I owned and felt like I was going to not be able to repeat his shooting knowing the rifle was capable. Well I did the same thing
and that is the same loading use to this day 12 years later. He is a 1 shot fawn killer!
Then after I bought my 7 th Edition Hornady manual I see this load is over maximum w/51.5 of 4350 listed as Max @2800 FPS
So as for the need to adjust COL just isn't always needed unless you are in to very long range bench rest shooting and need to tighten a group up a TAD.
I own a cheep cronograph but have never tested this load. I might have to do that some day just to compare with the manuals.
I have seen a few rifles at the range during sight in days do close to that good with factory ammo and the BAR .30-'06Spring being the one I see most.