Ruger manufactures their .243's with a 9 twist, so I don't believe twist is an issue.
I have a Ruger #1A in 7x57. Out of the box, it had the usual issue with the forearm contacting the barrel. I was just recently able to have a gunsmith fix the issue with a freefloat and bed job on the forearm.
While I did load development for it, I removed the forearm and made sure to rest the front bag directly under the action. Handled this way, it easily shot 3/4" groups with my handloads and with the Federal 175g factory load.
When it comes to handloading, I truly believe that it pays dividends to methodically work from minimum to maximum. I find that watching how the groups behave, not just group size, yields clues as to the location of "nodes" in the powder charge workup. Likewise, finding the rifle's preferred seating depth has proven to me to be an important key to unlocking the accuracy potential with a given bullet.
I believe many handloaders have the tendency to choose powder charges in a more random fashion, looking for the "magic" powder charge. Sometimes it is easy to find with a given rifle/load combination. Other times not. When an accurate powder charge is not easily found, the lack of methodical structure makes it difficult to see what the next step should be. The problem becomes a "finicky rifle" or "My rifle just doesn't like this powder/bullet/primer/brass/etc."
This is what has worked well for me:
Getting the Best Precision and Accuracy from Berger VLD bullets in Your Rifle
OCW Overview - Dan Newberry's OCW Load Development System
By personal preference, I like to test seating depth first then do my powder charge workup. You can reverse the two tests, though. It doesn't really matter. I have found the Berger seating depth test to work with just about any bullet from any manufacturer. While conducting these two tests, it has never taken me more than 50 rounds with a given bullet/powder combination to find my rifle's best load.
These two test procedures are just examples of how to proceed. There are other ways to do this stuff. The important thing, IMO, is having a methodical, repeatable load development procedure that tests the possible combinations from minimum to maximum loads in an efficient manner. I really think developing a methodology that works for you and that you have faith in, coupled with good record keeping, is the key to developing good loads with even "finicky" rifles.
When you come to the end of your test procedure, you will have seen your rifle's best work with the component combination you are using. If your test didn't yield anything acceptable, then it's probably time to go with a different bullet or powder.
I hope there is something here that proves useful to you. Good luck with your load development!