I have 2 AR's, in 300BO. One had the pistol type gas block and functions anything I have run thru it, even some very light subsonic loads. The other one will fire, eject the case, but does not come back far enough to pick up another round when shooting subsonics. It has the gas block out about 10 inches, the one that works with anything, about 7.5 inches, from the receiver. Do I need to change springs, and what do I need to get. All replies appreciated.