Steyr,

The final point I made was that put very simply, the Combro will stay still because it is not firmly attached to the rifle - it can slide along the barrel, and will slide along the barrel. More acurately, the barrel will slide under the Combro.

Just spoke to someone who'se got an FX, he says he uses it loosely attached with rubber bands also.

The Combro doesn't care what the rifle barrel is doing, it only cares abt the time it takes for the pellet to go through the two timing traps - and therefore will be accurate up to its specification. If it were firmly attached, the Combro would be moving back or forth due to recoil, and that would add or subtract from its result.

No doubt that is a simplification of real life but I stand by it!