SBoomer  - I had a highwall with a Buhmiller barrel in 218 Mashburn Bee back in the early 70's. It shot extremely well. I will check my notes in the morning and get back to you. We have better bullets available to us now, so possibly even better groups. 
 

My 044 1/2 in regular 218 Bee likes 4227.  I tried Lil Gun but the pressure gets high in a hurry.  Tom

With the Mashburn, you can have both, accuracy and speed. I never tried cast bullets, so can't speak to that. High velocity and cast bullets not usually a good pairing. On my way to the shop now. back
                      218 Mashburn Bee                                                    
                      Unertl 1" 10x                                                         
                      45 GR Sierra                                                             
                      16 GR IMR 4227                                                       
                      RWS primers                                                            
                      consistent 1/2" to 5/8" groups @ 100                                                             15 GR 4227 with 50 GR Sierras worked almost as well.                  There are lots of good bullets and new powders available to us since then. This might just be a good jumping off point. Best of luck, and I am sure you will be pleased. These loads were given to me by Neal Rice, who worked for Art Mashburn in the early sixties after he attended Trinidad gunsmithing school. He then left to serve in Viet Nam in 1968.

I very rarely settle for a factory round. There is something magic about the Ackley style shoulder when it comes to efficiency and brass flow. At any rate, I am having a ball with this new barrel. On a hunch, I tried a calculated load of 4759. Wow! I can see that I am going to have to put the 1/8 dot T36 on next. The crosshairs on the 20X STS nearly cover the 3/8” center paster.