I built myself a 6mm Ackley on a VZ-24. My reamer has the 40* shoulder. The barrel is a Hart #4 contour with a 1-7 twist finished at 26" long. 3225fps average with 107g SMK. It'll lay one on top of the other, repeatedly...... I had the barrel nitride. Using Reloader 22, Win. brass, Fed GM LRP. I haven't tried any bullets heavier than the 107g. I have fit a couple of barrels to Rem. LA for customers. The 6mm and the AI version fit the LA better than they do the SA,,,, especially if launching VLDs is the goal. The accuracy is in the barrel...... I did one for a customer on a Rem SA. He wasn't interested in anything heavier/longer than 87g varmint bullets. Took quit a bit of extra work to make that one feed trouble free. Wasn't exactly a 'drop-in'.