Before trying to blame the buffer or any other components for a clover leaf at 100m, I'd be more interested in knowing exactly just how much load development you've done for the rifle. Were you shooting factory loads, hand loads? There are many, many variables that come into play when "precision" shooting when it comes to just the load itself. Last summer I sold my F T/R bolt rifle that would put 5 rounds through 1 clean round hole at 100 yards with the load I had found for it but if I just changed even one variable in that load it would shoot all sorts of different patterns. It could be possible that your barrel doesn't like the 77gr SMK's. Just because you have a higher twist rate doesn't necessarily mean that your barrel will shoot them optimally in regards to POI, it just means that it can spin them fast enough to stabilize the much heavier round. In addition to the weight of the bullet, the powder or the primer could be a problem. If your powder has too high or too low of a burn rate, you may not be optimizing the potential of the powder. If it's too low, you could possibly only be using a partial amount of the powder as you would be blowing unspent powder out of the end of the barrel. If it's too high, you could be burning the powder too fast and not getting an even burn to keep the pressures high throughout the entire length of the barrel. If the primers aren't right, You could possibly be burning too much or too little powder upon primer strike. These are just a few of the issues to consider. The next thing, or possibly even the first thing that I would look at, is whether or not you're using a bipod, benchrest, bags, free hand, sled, prone, standing, sitting. When shooting "precision" any and/or all of these things can result in significant POI disparities. This is probably way too technical of a response in regards to what you were looking for but you did say that you're trying to do precision shooting. So in order to truly get precision results, everything you do up to that point must be precision oriented.