I have a Cooper Model 38. I am shoting 50 gr Berger and Vmax at 3024fps with 3/8 inch groups. Love it!What rifle is your Mashburn Bee. Over the last 45 years, I have owned a number of .218 Bees, both straight and Mashburn, and I love the cartridge. I have one now,a beautiful and very accurate Ruger #1)