As far as microgroove rifling goes I have no experience but as a machinist I understand the theory behind it. Seems to me it's similar to the difference between coarse and fine pitch threads. Sure the coarse threads look big and burly and strong but what makes the fine pitch in fact stronger is the increased surface area that actually distributes the load. So microgrooves may in fact work better than ballad, with a projectile that fits properly for the malleability and hardness of said projectile. Now we all know that the manufacturers do not produce firearms for the masses to shoot cast, the masses shoot jackets. Back to the thread theory, a fine thread of X diameter will strip in aluminum before a coarse thread of same diameter does in steel. This is obviously due to material strength, yield pressures, etc. So this probably is why microgroove is looked down upon by casters as I suspect copper is just that much bit harder to be able to function in microgrooves. That and it's cheap to put in a barrel. Let me disclaim this by saying that I do not in fact own a microgroove gun and have not even inspected the bore of one, and that the above is all pure cranial conjecture based upon hundreds of hours of gleaning knowledge from mainly this site. I will add however that I have read a post or three claiming very good accuracy with cast in microgroove barrels.