You're going to have problems shooting a 6.5mm bullet out of a barrel already made for a .277 bullet. Also, when did Nosler come out with a 27 Nosler? I know of the 26 & 28 Nosler?
Since I own and load for all 4 RUMs, I can say that the magazine is the limiting factor for OAL on all four. In fact, with my 7 RUM, I can't seat the bullets out far enough to touch the lands even if the magazine space would allow it. The longest OAL I can get is 3.67" and still function...
I've only used Nosler brass in 30-06, but haven't had any problems seating GM210M Fed primers. Time will tell if I have issues with my 338RUM brass I just got.
It's taken around 10 years to get to my current inventory of Nosler bullets, be it seconds or firsts. I gave the SPS watching a rest for a few years, but I'm back at it. You have to check it almost several times a day. The popular calibers and bullet types go really fast, like a matter of 30 min...
55.5gn of H414 flat works in my '06 with 180ABs.
TheBear_78 - what bullet are you using in your 375RUM. I'm using 7828SSC in my 375RUM with 300ABs and IMR4350 with 260ABs.
When I got my 338RUM, Graf & Son had primed Federal nickle 338RUM brass, so I bought about 300 of that. 6-7 years later no Fed nickle 338RUM to be found, so I choke a little on the price & order 100 pieces of Nosler 338 RUM 2nds.
Adding to the already great load info, these are the load recipes I have for my 30-06 Weatherby Vanguard Sporter:
Bullet: 180AB
Powder: 55.5gn of H414
Primer: Fed GM210M
Brass: Nosler trimmed to 2.48"
COL: 3.39" measure from tip to base
Average velocity: 2823fps
Load development target at 100M...
I started hunting in '03 with a hand-me down Savage M99 in 300 Savage - got my first hog with it. The first rifle I ever bought was a Win M70 270WSM at the Lompoc, CA Wal-Mart almost 12 years ago. I still have both of these, but I pretty much don't use the M99 any more.