I don't doubt that your headspace DID change, with the mounting of a new lug. It will, however, remain constant. You will have to reset your dies to match your current headspace (I'm sure you did this). What I was referring to, was the very slight bulging if the shoulder/body juncture, when you use a neck sizing die. That could cause you some hard-closing/lock-up difficulties.
In your original post, you cited smoked/dirty necks, different diameter necks in fired cases, and some concern about whether or not a bullet would fit in a fired case. Let's exclude a deliberately tight-necked chamber, say of benchrest proportions, for the time being. Given proper technique, a suitable pressure curve, and quality brass(Lapua certainly is), there is no reason you cannot assemble satisfactory handloads. You just have to eliminate the variables, one-by-one. The dirty necks tell me the pressure is low, period.
In a follow-up post, you cited difficulty opening. Did the "barrel drop" sequence stop when the extractor hit the cam? Or, was the finger lever just hard to depress? I define sticky extraction as where the barrel will unlatch, but stops when it gets to the point of extraction. You then have to press down on the barrel, or give it an up-and-down shake, to effect extraction. I would do a chamber cast, at any rate. You can get some pretty good info from it.
Do some more shooting, and let us know what the results are. Sorry for goin' on so, but I do have a real interest in helping to correct your difficulties, and also, I love a challenge like this.>>>>>>>>Bug.
