I finally got my 264 and managed to get out for a bit on Saturday to break it in and shoot some of the RL33 loads. The rifle is a Model 70 26" Sporter. Very thin barrel, I'm figuring about a #2 size. Heats up fairly quickly.

Loads started at 69 grains up to 74. First decent group came at 70 grains with a 3-shot group of .75". Chrono'd a couple of rounds and was rather disappointed at the 2875 fps. 71 grains opened up to a 1.5 inch group with each shot running about .5 inch from the previous shot at the 1 o'clock location. Had to stop there as had things on the schedule. I hope to get out and shoot the rest of the loads sometime this week but, not holding my breath looking at my schedule.

What bullet?

142 LRAB

I use Retumbo in mine. 120 gr Nosler with Fed Match primers doing 3350. I've been fortunate to have numerous opportunities on deer and pronghorn from 300 - 450 yds. All have dropped immediately.

Haven't seen Retumbo out here in 2 years.

I've also loaded up some rounds with 7828ssc to see if they'll do any better.

The barrel is a 1-10" so this may just be a bit too long of a bullet to stabilize no matter what powder I try. If this doesn't work, I'll drop to the 130 range and try again.

Is this a current production rifle ?
I've never heard of a 1/10 twist 264 Win.
The current offerings from Winchester are 1/9 according to their website.

IMHO a 1/9 264 makes very little sense unless you are planning to shoot 120-125 gr bullets.
I built mine w a 28 inch 1/8 barrel in order to stabilize the 130-142 gr bullets.
My loads use WC872 a military ball powder used to load 50BMG and 20MM Vulcan ammo.
The burn rate is equal to H870 which has been discontinued.
RL33 should be about the same range.
I'm getting 3350 FPS with 130 Accubonds and 3400 with 130 Bergers.

My 1/9" 264 shoots bug holes with 140 GKs

At what kind of velocity ?