Remember that you are comparing the RUM case to the Lapua case. Two different animals. I have many wildcats developed on both. THe standard RUM case and the standard Lapua case are nearly identical in case capacity, within 1 grain either way most of the time.
When loaded to identical chamber pressures, they will make nearly identical velocity.
The improved version of the Lapua will give you 10-12% case volume increase but that does not translate into 10-12% velocity increase, in fact its more like 2-3% increase in velocity.
The main advantage that the Lapua wildcat has is dramatically stronger case strength. If you load the RUM up to a point where you will start to loosen primer pockets in 4-5 firings per case, you will likely be in the 3100 fps range with the 300 RUM and the 230 gr bullet weight even in a 31" barrel. May be a bit more then this but if your looking for legit 3200 fps, I suspect your going to really cut your brass life.
The Lapua parent case however will take 70,000 psi of chamber pressure and not complain one bit so right there you will get a significant boost in performance over the RUM.
In all my testing, which compares the 7mm RUM vs my 7mm Allen Magnum, 300 RUM vs my 300 Allen Xpress, the 338 Edge vs my 338 Allen Xpress and the 375 RUM vs my 375 Allen Xpress. In every case, when using heavy for caliber bullets, the improved version of the Lapua case will add 150 fps on top of what the RUM case will produce.
I would be a bit suspect of the claims of nearly 3350 fps with the 230 gr in a 30-338 Lapua Improved. Must be a very fast barrel. Out of a 1-8 twist, that throws some red flags up. In a 30", 1-8 twist barrel, my 300 Allen Xpress will drive a 230 gr to just shy of 3300 fps and it will drive a 240 gr SMK to 3225 fps using Retumbo. I have not tested RL-33, mainly because its nowhere to be found.
Now, that said, all of my loads were loaded to a pressure level that NEVER loosened a primer pocket even after 10 firings. In my load development, I did push things over 3300 fps easily but chamber pressures were to the point where primer pockets were loosening after 3-4 firings on the Lapua parent case.
If your loosening a primer pocket on a 338 Lapua case, your pushing chamber pressures over 70K psi. I would not recommend that.
As far as the twist rate you should use for the 230 gr . I would say use what Berger recommends. A commercial bullet maker is going error on the conservative side for recommended twist rate. Remember that this bullet could be used in anything from a 30-06 up so they are going to recommend what has been proven by them to work on the less rounds as its clear that the faster magnums will need slightly less velocity to maintain stability.
I work with Berger alot on new bullets. They send me prototypes and ask me to try to destroy them with velocity out of my Allen Xpress and Allen Magnum chamberings. I was sent the 230 gr Hybrid when it was new and I tested it out of my 300 AX and pushed it to 3400 fps with proof loads (far higher then what should ever be used) and out of a 1-8 twist barrel at that. Accuracy was better at around 3300 fps but there were no bullet failures of any kind.
I also tested them in a 1-10 twist 300 AX with a 27" barrel length and performance and accuracy was great so I would think that in the slightly slower 300 RUM, you will see no issues.
They have proven themselves to me in twist rates from 1-8 to 1-10 and at velocities from 3000 to 3400 fps so in all reality, I do not think it will matter at all if you go with a 1-9 or 1-10 twist barrels.
Just stay realistic with your velocity goals. Personally, I would not expect to see much over 3100 fps with this bullet weight on average out of a 31" barreled RUM. Not saying you can not get more, just saying you will give up brass life by doing so.
thats what i am considering doing.
