Measuring case head squareness

[lrgoodger]

Can a Sinclair concentricity gauge be used to measure case head squareness? If so, how would one go about it? If not, what is the best tool to use for that?

 

[bigedp51]

 

[Phil3]

I wanted to know this too, but used an approach I doubt you have available to you. I used a lathe and test indicator. The case went into the shell holder from a Sinclair trimmer, and that shell holder (chunk of steel), was put in the lathe chuck. It was easy to measure the flatness of the case head by slowing rotating the chuck and watching the indicator. Note: The head stamp complicates matters as the indicator tips moves as it rides over the indentations.

Using the trimmer, I also reversed the trimmer shell holder and trimmed the case head ever so slightly to make it flat. In an AR-15, which can be rough on the brass, this was helpful to ensure I was measuring a case without burrs on the case head.

I am sure there are other approaches, but nothing else comes to mind right now.

Phil

 

[Lapua40X]

Whenever you're reading run out, the results can only be as accurate as the degree of care taken in set up. When the support mechanism (lathe, case trimmer or other device) has a runout >0 the error will be amplified over the length of the case and result in an inaccurate reading at the case head.

 

[STS]

I thought this through pretty carefully about 30 years ago and came up with this. If unfired brass is not square in the case head, it soon will be after the first firing, assuming the bolt face is square in the rifle. If the bolt face is not square in the rifle, no amount of squaring of the case head by mechanical means will prevent it from becoming crooked every time it's fired. You would be forced to cut the case head square after each firing which is not a practical way of dealing with the problem. The bottom line is, leave the case head alone and make sure the bolt face is square in the rifle. Problem solved.

 

[lrgoodger]

I thought this through pretty carefully about 30 years ago and came up with this. If unfired brass is not square in the case head, it soon will be after the first firing, assuming the bolt face is square in the rifle. If the bolt face is not square in the rifle, no amount of squaring of the case head by mechanical means will prevent it from becoming crooked every time it's fired. You would be forced to cut the case head square after each firing which is not a practical way of dealing with the problem. The bottom line is, leave the case head alone and make sure the bolt face is square in the rifle. Problem solved.

You know, I thought about that. If you have a case head out of square after firing it, you have a problem. I think the odds of that being something I need to worry about are pretty slim on this BAT MB action with Lapua brass.

Thanks

Ron

 

[signut]

That makes good sense; I can't imagine adding another step in brass prep!!

 

[STS]

Ron, I'd say there is little chance that your Bat action is not square with the world, but it's important to remember it only makes up half of the equation. The barrel has the chamber in it, and the chamber must be square with the bolt face as well. The barrel could be significantly out in relation to the bolt face, but if the fellow that chambered the barrel is worth a hoot everything is square and you have no worries.