I have been considering building a 7SAUM or 6.5 GAP 4S. With long, high bc bullets, I am not sure I could get the full potential out of either on a short action. My concern is how will they feed from a long action. Should I run them with a detachable mag system? Or am I waisting my time with these cartridges and just go with a 7 rem mag or 264 win mag if I'm going with a long action?