JayKelley wrote:
The line has to be somewhere. If 4.13 is ok, how about 4.18?

Rule says 4.1 or less. 4.13 does not meet that criteria.

Engineer brain engaged.  What is the precision on the 4.1.  The rule states 4.1 or less, but does not stipulate precision or measurement techique.  What about 4.13? I could see that much length over spec pretty easily with a good ruler.  What about 4.103?  You would have a very hard time seeing that on a ruler.  How about 4.1003?  You would have a hard time measuring that with a pairs of calipers.  It would be nice if a technique and precision was stated in the rules.  Few years ago USPSA had a bit of a blow up over magazine lengths.  Despite the fact that there was a stipulated measurement and an official gauge people where getting different results depending on how they used the gauge.  They added additional text to the rule book stipulating the correct technique on how to use the gauge.  Similar might be helpful for IDPA barrel length measurement.

Example: Measure barrel length with a dial or digital caliber with a minimum accuracy of +/-0.001 inch.  Semi-auto barrels are measure from the breach face to the longest point on the muzzle end of the barrel with action closed.  Revolver are measured in a simlar maner but from the face of the cylinder to the further point on the muzzle end of the barrel (cylinder may be turned to facilitate puting the caliper depth rod on cylinder face).  Measurements will be made to the third decimal point then round off to the second decimal point using standar rounding rules.  (ie 4.105 = 4.11 and 4.104 = 4.10)  Barrel must be 4.10 or less.

Obvously the precision could be tweeked but it is clear in both precision and technique.  There would be very few arguments over whether a barrel was legal or not using the above techique.

I would ask, why put a barrel length specification at all for divisions that have to fit in a stipulated box?  Why the extra constraint?

-Matthew