I took my M&P out for the first time since changing to a midlength barrel this weekend. I had already had the Spikes H2 buffer in there because it was over gassed out of the box and had timing issues ie: "FTE and FTF". Anyways, I found that after switching to the midlength gas system that I did need to go back to the original buffer. I had a couple of FTE and had a situation where the bolt jammed on top of a half stripped bullet. Shot flawless after the switch! I was shooting a variety of 62gr and 55grs though, the H2 might have been ok with heavy heavy ammo but im looking for overall reliability.