Loaded round vs. neck diameter measurements

[butchlambert]

Maybe to prevent a too much imperfect concentricity betwixt the case body (and shoulder) and the bullet’s bearing surface from causing a too closely fitted neck to contact the chamber’s neck wall and then put in a bind the bullet whose bearing surface is poked up into the throat area where there’s possibly, at best, less than a quarter thousandth’s clearance on any side ...?

Not bad, but only a factory rifles should have problems. A properly reamed chamber with a properly size case, and a bullet seated properly will be aimed properly with say a .004 neck also. A hunting rifle(Factory) will never know the difference on paper.

 

[nmkid]

The reason I bring this up...My first 6-284 supposedly had a .280 neck. I was using Lapua 6.5-284 brass necked down and turned to .015. I was getting all kinds of black soot on all my fired cases and 1 case ejected with a split neck. This was with about 100-125 rounds down the barrel, (if I remember correctly). I sent the barreled action to PacNor for a new barrel with a .270 neck. In the meantime I broke down the few loaded rounds I had left and for the life of me I can't remember what a loaded case measured at the neck. However, I do know I was using a bushing .002 smaller then a loaded round measured. Crazy thing was...It shot pretty good anyway. The gun exhibited the black soot on all my cases during the time I spent trying to find a, "load" for it. I never shot a "maximum" load and used the same primers through out, (CCI BR). Powders tried, H-1000, RE22, Retumbo and 4831SC. I posted this problem a few months ago and I don't feel I received any opinion that explained what was happening. Not knowing for sure, I feel that there was too much clearance in the neck area and it wasn't sealing properly when fired. Thus the black soot on the cases. Granted, I have nothing to prove that was happening. Just my uneducated guess. So, I was hoping to get some info on how much smaller a loaded round should be then the neck diameter. Hope my rambling makes sense.

 

[chino1969]

So what ya thinking.. .266-.268 loaded ?

Yup

 

[jdh47]

If you are turning your necks down that could contribute to the soot. Split necks come from brass work hardening. That can be cured somewhat by annealing but nothing lasts forever.

Joe