Question on Wilson Case Gage

[Tom15034]

The base of my 6mm BR fired Lapua brass sticks out of a Wilson case gage .004-.008", depending on how hot the load was. New unsized brass sticks out less than .001". Does this mean my chamber is too long?
Tom

 

[StephenPerry]

Tom
Your 6 BR fired cases are responding to the length of your chamber. Headspacing is measured from the base of your case to shoulder contact in you barrel chamber. OAL of your fired cases do not indicate head space. FL sizing dies push case shoulders back in a sense you are adjusting your heapspace by sizing. The Wilson gage you are using is a trim gage not expected to indicate headspace. What you see coming out of the gage can be trimmed off if you want or left alone. The throat section of your barrel allows for case growth. Trim them all back to 1.555 if you want, no harm there.

Stephen Perry
Angeles BR

 

[BoydAllen]

Stephen,
If one looks at a chamber drawing, it is evident that the neck portion of the chamber is a different diameter than the throat, and that there is an angled transition between the two. If one does not trim cases to keep them below the maximum,the distance from the bolt face to the beginning of of the angled transition), it is possible that the case mouth will be crimped into the bullet as the bolt is closed, thus significantly raising chamber pressure to possibly unsafe levels.

As to the headspace problem, I find it curious that an unfired case would protrude from the gage by any amount, and would agree that the gage is not intended to be used as a headspace gage, but rather to compare the base to shoulder distances of fired and sized cases as well as to monitor neck length. A headspace gage is the correct tool to answer the question. As an aside, it is possible that a case can be the correct length, but have the shoulder pushed back far enough, by incorrect sizing that the neck is too long for the chamber.

 

[StephenPerry]

Boyd
What else is new. The guy is only dealing with .004-008 outside the case gage. Not a major calamity here. I notice when I turn necks OAL goes up .004 in a Lapua case, not a problem. We can't make all these questions into Competition BR Case Prep questions. The gentleman's question is an RCBS case prep questions that many manuals handle very well. I'll only comment on your initial analysis, he is no where near a case length that would produce the crimping example you gave, he needs to state what his OAL is when he is .004-.008 outside case length gage since 6 BR is defined as 1.560 a length of 1.568 is not going to break the bank. I don't recommend running over the case gage length but it is an easy fix. His curiosity with the gage is understandable. If you reread I suggested he trim back to 1.555, better yet 1.550. Can't comment or relate to the crimping comment, never experienced that problem.
Back to my bullet making Boyd. Making 22's for my Rail. Next month at Visalia SW Region 10 shot Unlimited.

Stephen Perry
Angeles BR