That sounds like a very nice rifle you have, especially for venturing into high velocity cast bullet shooting. With the 14.5" twist bullets longer than about 1.03" will not stabilize well until you get well above 2000 fps. I've found, after extensive testing and a bit of frustration, in my own 14" twist Palma .308W rifle that bore riders of about the length of the 311041 and MP 311-180 (170 & 180 gr) are about the heaviest that can give very good accuracy upwards of 2500+ fps. I did work with the 311299 and found it gave acceptable hunting accuracy when pushed hard upwards of 2400+ fps. How well your slightly slower twist rifle would do with those bullets remains to be answered.
If you want the best accuracy at high velocity (I'm talking 2500 to 2700+ fps) then the bullet of choice needs to have these attributes;
Bearing surface with GC top not below the neck/shoulder junction to the ogive just touching the leade.
A short nose with no bore riding section.
Minimal groove width and depth with just a sufficient amount of lube capacity.
There is one bullet that was specifically designed to meet those requirements. That is the NOE 310-165-FN (30 XCB). It has been thoroughly tested from "normal" cast bullet velocities in the mid teens up through 3300 fps. In my own 14" twist Palma rifle I shoot it at 2600 fps and maintain excellent accuracy to 600 yards with it. At 2600 fps 10 shot groups hover around 1 to 1.3 moa out to 300 yards and 1.5 to 2 moa accuracy out to 600 yards. Pushing a cast bullet that fast is hard on the bullet and the best accuracy is in the 2300 - 2400 fps range.
The second best bullet I like to use is the 311466 which fits the criteria with the exception of the lube groove size. I have a 4 cavity Lyman 311466U that casts perfect bullets for such HV use in the 308W cartridge. These day, again, I would look to NOE as their 311466 is an excellent one.
For an alloy I have found Lyman #2 to give the best consistent accuracy, even over straight linotype. I also WQ the bullets which runs the BHN up to 22 - 24. The bullets are cast in lots of 600 - 800 at a session and then inspected and weight sorted. A close visual culling for any defect no matter how small is done and the sprue is cut off smooth with a sharp knife. The bullets are then weight sorted. I used a different weight sorting method and it has been posted here on the CBA forum and I suggest a thorough read. The GC (Hornady) are seated separately then the bullets are lubed in a Lyman 450 with an H&I die of "as cast" diameter. The GC'd and lubed bullets are then Sized in a Lee push through that has been honed out to give the proper size wanted (to just fit into the throat of the chamber).
I have thoroughly tested 13+ lubes at high velocity and found 2500+ to be the best of currently available lubes.
The cases used must be of one lot and uniformly "match prepped". I use Winchester .308W "PALMA" cases (marked on the head stamp) and Some LC 72 Match (M118 White Box) cases. The necks are lightly turned/reamed for concentricity.
Powders; You'll want to use a slower burning powder that gives close to, if not 100% load density. I've found AA4350 to work best in my .30W and 30x60 XCB rifles with either the 30 XCB or 311466 bullets. However, RL15, RL17, IMR4350 and H4350 also work well. To get velocity you must have pressure. You will be pushing 40 - 50,000 psi to push either bullet into the true high velocity range. The trick with the powder used is to use the slowest burning powder that gives 100% load density and the velocity desired......and is accurate. I have not had very good results with any ball powder. LeveRevolution also works well but does not give 100% load density at 2600 - 2700 fps so a small Dacron filler was used with it. As with most firearms your rifle may show a preference for a particular powder but one of these mentioned is going to work the best for your rifle.
I've not found much difference in primer choice except that the load must be worked up with the primer used. Switching to a different primer most often isn't hazardous but it can alter the time/pressure curve which can have an adverse affect on accuracy. I use Winchester WLR primers.
As far as loading technique I suggest a technique that gives the most consistent and concentric rounds. I NS so the neck is a hard fit onto the expander mandrel in my .31 caliber M-die using a Redding bushing die. The M-die then irons out and expands to the correct neck tension for the .311 sized cast bullet.
I seat the bullets so they just are a tight fit onto the leade just as the bolt closes.
That's a quick glimpse at what I've learned to do to shoot exceptional cast bullet accuracy at high velocity. It definitely is a learning curve and can be frustrating. From experience the worst hold ups to success was when I listened to advise from "experts" on how it should be done even though they'd never actually done it. It took me 10+ years to figure it out and thousands of test groups There was success by a few in the past and it was from them that myself and several others learned from them stumbled ahead and figured it out. It is "rocket science". You can vary technique and still be successful. However, you will not be successful thinking you can bend or ignore the laws of physics and ballistics regardless of the "expert" advise given. I do not claim to be an expert by any stretch. However, I have been there and done that (high velocity cast bullet shooting with accuracy to extended ranges) and have learned what it really takes to get there.
Keep a shot count record as with those loads the barrel will get eroded. I have over 3000 full throttle (53 gr AA4350 under the 30 XCB with 48 - 50,000 psi) rounds out of my 30x60 XCB and can see, with a bore scope, some erosion in the leade and just ahead of it. As they say; "If you're going to dance, you have to pay the band."
I've found shooting cast bullets at HV to be very rewarding. This last spring I shot PDs from 300 to 500 yards with a 70+ % hit ratio with the 30x60 XCB bullet at 2900 fps. I've shot numerous 600 yard 1 to 1.5 moa 10 shot groups with it also. I've also shot 1.5 to 2 moa groups at 600 yards with the Palma .308W. Recently a Canadian friend shot 1.5 moa at 550 yards with his own 30 XCB bullets. So, welcome to HV shooting. I'll be glad to answer any questions and help any way I can.
Concealment is not cover.........